                IN THE SUPREME COURT OF IOWA
                                  No. 17–1458

                               Filed May 10, 2019


THE CARROLL AIRPORT COMMISSION,

      Appellee,

vs.

LOREN W. DANNER and PAN DANNER,

      Appellants.



      On review from the Iowa Court of Appeals.



      Appeal from the Iowa District Court for Carroll County, William C.

Ostlund, Judge.



      A farmer seeks further review of a court of appeals decision

declining to give preemptive effect to a no-hazard determination by the

Federal Aviation Administration. DECISION OF COURT OF APPEALS

VACATED; DISTRICT COURT JUDGMENT AFFIRMED AS MODIFIED.



      Steven D. Hamilton of Hamilton Law Firm, P.C., Storm Lake, for

appellants.



      Gina C. Badding of Neu, Minnich, Comito, Halbur, Neu & Badding,

P.C., Carroll, for appellee.
                                    2

WATERMAN, Justice.

      In this appeal, we must determine the legal effect of a “no hazard”

letter issued by the Federal Aviation Administration (FAA) to a farmer

who built a twelve-story grain leg (bucket elevator) near an airport. The

structure intrudes sixty feet into airspace restricted for aviation.

Construction was well underway when a member of the local airport

commission cried foul. The airport commission informed the farmer he

needed a variance and refused to grant one, without waiting for input

from federal officials.   Shortly thereafter, the FAA investigated and

granted a no-hazard determination, approving the structure on the

condition the farmer paint it and place blinking red lights on top, which

he did. The FAA also adjusted the flight path. This did not satisfy the

local commissioners, who two years later filed this action in equity to

force the farmer to remove or modify the structure. The farmer raised an

affirmative defense that the federal no-hazard determination preempted

the local regulations.

      The district court, sitting in equity, rejected the preemption

defense and issued an injunction requiring the farmer to remove or alter

the grain leg at his expense and imposed a daily penalty after a nine-

month grace period to abate the nuisance. The farmer appealed, and we

transferred the case to the court of appeals, which affirmed the rejection

of his preemption defense.      We granted the farmer’s application for

further review.

      On our de novo review, we determine that the Federal Aviation Act

allows for local zoning regulation, and the no-hazard letter did not

preempt the local airport zoning regulations as a matter of law.      We

affirm the district court’s finding the structure constitutes a threat to

aviation requiring abatement.     But we conclude that the $200 daily
                                    3

penalty should be vacated, and the nine-month period to modify or

remove the structure shall begin anew when procedendo issues.         We

affirm the district court judgment as modified.

      I. Background Facts and Proceedings.

      Loren and Pan Danner, husband and wife, live on a farm they own

in Carroll County, Iowa. Loren has been farming this land since 1968.

Loren formerly raised livestock but has exclusively grown row crops on

the land since 2000. The Danner farm sits under the flight path to the

Arthur N. Neu Municipal Airport, a facility managed by the Carroll

Airport Commission (the Commission). Local zoning ordinances mandate

a protected zone around the airport that extends 10,000 feet horizontally

from the end of Runways 13 and 31 into an arc 150 feet above the

airport. The Danners’ farm sits within this zone.

      In 2009, after a particularly good harvest, Loren realized he needed

to find a way to more efficiently dry and store harvested grain.       He

considered multiple options, but ultimately decided to construct a grain

leg (also known as a bucket elevator) with attached storage bins. Loren

and two farm neighbors built five grain-storage bins of varying sizes on

the Danners’ farmland. The five bins stand in a semicircle around the

grain leg. The grain leg is a 127-foot-tall structure with separate metal

tubes sloping down from its top to each storage bin.

      The grain leg stands within 10,000 feet horizontally from the end of

Runway 31. The top of the structure is 1413.43 feet above mean sea

level. The protected airspace above the airport is 1354 feet above mean

sea level. The structure reaches a height of 127 feet off the ground. The

parties agree the grain leg intrudes within the airport’s protected

airspace by approximately sixty feet.
                                     4

      In January 2013, before beginning construction of the grain leg,

Loren went to Carl Wilburn, the county zoning administrator, to obtain a

building permit.   Wilburn issued the building permit and granted the

Danners an agricultural exemption from the county zoning ordinances.

The agricultural exemption, however, did not exempt the Danners from

the airport zoning ordinances.    The building permit application states,

“All farm buildings or structures are subject to the Airport Zoning

Ordinances which regulate[] height and emissions in and around the

airport air space as depicted on the attached diagram[.]” The diagram

attached to the permit showed the airport’s protected airspace. Despite

this warning on the building permit application, neither the Danners nor

Wilburn realized that the agricultural exemption did not exempt the

grain leg from the airport zoning regulations.      For that reason, the

Commission was never notified of the Danners’ application for a building

permit, and the Danners failed to request a variance from the airport

zoning ordinance. Construction of the grain leg began in April and was

completed in August.

      Meanwhile, in June, Commissioner Greg Siemann noticed the

grain leg construction and became concerned.          The next day, he

contacted Wilburn and Greg Schreck, the city zoning commissioner.

Wilburn informed Siemann that he had issued a building permit to the

Danners with an agricultural exemption and acknowledged he was

unaware of the local airport zoning restrictions.

      The Commission notified the Danners that the grain leg required a

variance from the airport zoning regulations and informed the Danners it

would not consent to the violation of the regulations or grant a variance.

The Commission asked the FAA to perform an aeronautical study of the

grain leg and its impact on aviation safety.
                                     5

      In July, after performing the aeronautical study, the FAA issued a

“DETERMINATION OF NO HAZARD TO AIR NAVIGATION” letter, stating

in part, “This aeronautical study revealed that the structure does exceed

obstruction standards but would not be a hazard to air navigation” if the

Danners met certain conditions.      The FAA instructed the Danners to

paint the structure and add red lights to the top of it. The no-hazard

letter warned the Danners,

      This determination concerns the effect of this structure on
      the safe and efficient use of navigable airspace by aircraft
      and does not relieve the sponsor of compliance
      responsibilities relating to any law, ordinance, or regulation
      of any Federal, State, or local government body.

The Commission did not seek judicial review of the no-hazard

determination as permitted under federal law. See 14 C.F.R. §§ 77.37,

.39, .41 (2013).   The Danners complied with the FAA’s instructions,

adding lights and painting the grain leg. The FAA issued a “Notice to

Airmen” (NOTAM) that raised the minimum descent levels for the airport

by 100 feet, requiring pilots to approach the airport at a higher altitude.

      Two years later, in July 2015, the Commission filed this action on

the district court’s equity docket alleging the grain leg violated certain

building ordinances, city and county zoning ordinances, and airport

commission regulations, and constituted a nuisance and hazard to air

traffic. The Commission sought equitable relief—an injunction requiring

the Danners to modify or remove the grain leg.       The Danners filed an

answer and jury demand. The Danners raised an affirmative defense of

federal preemption. The district court struck the jury demand because

the case was filed in equity. The case proceeded to a bench trial.

      At trial, the following witnesses testified for the Commission:

C. Peter Crawford, the engineer for the airport; John McLaughlin, a
                                      6

meteorologist, pilot, and flight instructor; Donald Mensen, fixed base

operator of the airport; Kevin Wittrock, a commissioner and a pilot; and

Siemann, an attorney, pilot, and commissioner. Loren Danner testified

on his own behalf. No pilot or aviation expert testified for the Danners.

      Crawford testified about the engineering survey of the grain leg in

relation to Runway 31 of the airport. The survey showed that the grain

leg was 7718 feet from the end of Runway 31 and within the airport’s

protected zone.

      The other witnesses gave opinion testimony that the grain leg

constituted a hazard to aviation.         The pilots testified about their

experiences flying over the grain leg when landing at the airport and

expressed their concerns for student pilots or pilots distracted while

landing.   The Commission also presented testimony that the grain leg

would jeopardize the airport’s ability to secure federal grant money. The

record indicates, however, that the airport received two federal grants,

one for $284,466 and another for $263,200, after the Danners installed

the grain leg.

      Loren testified that it cost approximately $274,928 to construct the

grain leg, $32,942 to install a concrete drive-over pad, and $8000 for an

electrical contractor. Loren testified that if the height of the grain leg was

reduced, he could no longer rely on gravity to move the grain from the

distributor to the storage bins.       Instead, he would need to install

conveyors. Loren estimated that the cost to tear down the grain leg and

rebuild it with conveyors to each of the storage bins in compliance with

the zoning regulations would be approximately $450,000.           These cost

figures went unchallenged.

      In June 2017, the district court found that the grain leg violated

state and local zoning ordinances and constituted a nuisance and an
                                     7

airport hazard under Iowa Code sections 329.2 and 657.2(8) (2015). The

court found that the grain leg did not fall within the agricultural

exemption to certain zoning laws.        The court rejected the Danners’

affirmative defense that the no-hazard letter preempted state and local

zoning laws, stating,

            While the FAA regulations certainly do apply, the local
      county regulations can also be in effect.          The local
      regulations take a more stringent stance on what a hazard is
      and how it could affect the air space. If the FAA regulations
      contained all airport and safety regulations there would be
      no need for the State to designate zoning powers to the
      Commission. The Court finds that these regulations in fact
      work together and the FAA regulations and letter sent do not
      preempt the local regulations.

The district court gave no evidentiary weight to the FAA’s aeronautical

study and no-hazard determination.        The district court ordered the

Danners to either remove the grain leg or modify its height to comply

with the local regulations regarding the airport’s protected airspace. The

Danners filed a motion for judgment notwithstanding the verdict and a

motion for new trial in light of our ruling in State v. Martinez, 896 N.W.2d

737 (Iowa 2017) (addressing preemptive effect of federal immigration

laws). The district court denied the Danners’ motions.

      The Commission moved pursuant to Iowa Rule of Civil Procedure

1.904(2) to enlarge the order to set a date certain for abatement and to

impose a daily penalty after that date.     On September 5, the district

court, after conferring with counsel, set May 1, 2018, as the date by

which the Danners had to remove the grain leg or lower it by sixty feet,

with a $200 per diem penalty every day thereafter accruing against the

Danners jointly and severally.

      The Danners appealed.      We transferred the case to the court of

appeals. The court of appeals affirmed, concluding that the doctrines of
                                      8

express, implied, and conflict preemption did not apply to the FAA no-

hazard determination.        The Danners filed an application for further

review, which we granted.

      II. Standard of Review.

      The parties disagree as to the standard of review. The Commission

contends the case was tried as a law action because the trial court ruled

on objections.    The Danners contend the case was tried in equity.

“Generally, our review of a decision by the district court following a

bench trial depends upon the manner in which the case was tried to the

court.” Collins Tr. v. Allamakee Cty. Bd. of Supervisors, 599 N.W.2d 460,

463 (Iowa 1999). If the case is tried at law, our review is for correction of

errors at law. Id. “Our review of cases tried in equity is de novo.” City of

Eagle Grove v. Cahalan Invs., LLC, 904 N.W.2d 552, 558 (Iowa 2017).

      We conclude this case was tried in equity. The Commission filed

the action in equity and sought only equitable relief—a permanent

injunction. Notably, the district court struck the Danners’ jury demand

based on its ruling that this is an action in equity.      Accordingly, our

review is de novo.     Id.   “Nevertheless, we give weight to the factual

findings of the district court, especially with respect to determinations of

witness credibility.” Id.

      Preemption, however, is a question of federal law. See Martinez,

896 N.W.2d at 746–47; Freeman v. Grain Processing Corp., 848 N.W.2d

58, 75 (Iowa 2014) (reviewing principles of federal preemption).        “We

review the district court’s legal conclusions for correction of errors at

law.” Walnut Creek Townhome Ass’n v. Depositors Ins., 913 N.W.2d 80,

87 (Iowa 2018).
                                          9

       III. Analysis.

       We must decide whether the FAA’s no-hazard determination for the

Danners’ grain leg preempts state and local zoning ordinances limiting

the height of structures in or near flight paths.           The Danners rely on

Martinez, contending our recent acknowledgment of the supremacy and

sweeping preemptive effect of federal immigration law in that case

supports preemption under federal aviation law here.               In Martinez, we

held federal immigration law preempted the state criminal prosecution of

an undocumented worker for using false identity papers to gain

employment. 896 N.W.2d at 757. 1 Federal immigration and aviation law

alike can supersede conflicting local regulations.            At first glance, the

Danners have more to argue in favor of preemption than Martha Aracely

Martinez, who lacked a specific finding in her favor by federal authorities.

By contrast, the FAA specifically investigated the Danners’ grain leg and

issued a no-hazard determination (subject to conditions, which they

satisfied).   Federal aviation law, however, allows room for local zoning

regulation.    In our view, Martinez is not controlling here, and we will

focus our analysis on aviation law and court decisions addressing the

legal effect of FAA no-hazard determinations.
       We first address the Federal Aviation Act and the federal

regulations promulgated to implement the Act’s safety standards.                  We

next address Iowa state and local laws regulating structures near

airports. We conclude federal law and the FAA no-hazard determination

allow for local regulation of tall structures in flight paths, and the district

court correctly rejected the Danner’s preemption defense.

        1The United States Supreme Court granted certiorari in another case addressing

the preemptive effect of immigration law on state criminal prosecutions for identity
theft. State v. Garcia, 401 P.3d 588, 599–600 (Kan. 2017), cert. granted in part, 139
S. Ct. 1317 (2019).
                                          10

       A. Federal Law.

       1. The Federal Aviation Act.         The Federal Aviation Act of 1958,2

codified as amended at 49 U.S.C. Subtit. VII, was created “for the

purpose of centralizing in a single authority . . . the power to frame rules

for the safe and efficient use of the nation’s airspace.”             Air Line Pilots

Ass’n, Int’l v. Quesada, 276 F.2d 892, 894 (2d Cir. 1960). Pursuant to

the Act, “[t]he United States Government has exclusive sovereignty of

airspace of the United States.” 49 U.S.C. § 40103(a)(1) (2017).

       The Administrator of the Federal Aviation Administration
       shall develop plans and policy for the use of the navigable
       airspace and assign by regulation or order the use of the
       airspace necessary to ensure the safety of aircraft and the
       efficient use of airspace.

Id. § 40103(b)(1).

       The Administrator “shall promote safe flight of civil aircraft in air

commerce by prescribing . . . regulations and minimum standards for

other practices, methods, and procedure the Administrator finds

necessary for safety in air commerce and national security.”                        Id.

§ 44701(a)(5).     These safety standards apply to airports such as the

Arthur N. Neu Municipal Airport. Id. § 44701(b). The Administrator is
directed to carry out the safety regulation “chapter in a way that best

tends to reduce or eliminate the possibility or recurrence of accidents in

air transportation.” Id. § 44701(c).

       As one aspect of airport and aircraft safety, the Act regulates the

construction of structures that interfere with airspace.               This includes

prescribing notice requirements for individuals who seek to build or

expand a structure. Id. § 44718(a). The Act provides for aeronautical

       2Both   the Federal Aviation Administration and the Federal Aviation Act are
referred to as the FAA. In this opinion, we refer to the Federal Aviation Administration
as the FAA and the Federal Aviation Act as the “Aviation Act” or “the Act.”
                                      11

studies to determine the impact of the proposed construction.               Id.

§ 44718(b).      During    an   aeronautical    study,   the    Secretary   of

Transportation must

             (A) consider factors relevant to the efficient and
         effective use of the navigable airspace, including—
              (i) the impact on arrival, departure, and en route
            procedures for aircraft operating under visual flight
            rules;
                (ii) the impact on arrival, departure, and en route
            procedures for aircraft operating under instrument
            flight rules;
              (iii) the impact on existing public-use airports and
            aeronautical facilities;
              (iv) the impact on planned public-use airports and
            aeronautical facilities;
               (v) the cumulative impact resulting from the proposed
            construction or alteration of a structure when combined
            with the impact of other existing or proposed
            structures; and
              (vi) other factors relevant to the efficient and effective
            use of navigable airspace[.]

Id. § 44718(b)(1)(A)(i)–(vi).   To implement the Act’s requirements,

Congress empowered the FAA to promulgate regulations. Id. § 40103(b).

      2. The federal regulations. Title 14, part 77 of the Code of Federal

Regulations sets forth notice requirements for proposed construction,

guidance on determining whether proposed construction or an existing

structure is an obstruction to air navigation, the aeronautical study and

hazard/no-hazard determination process, and the procedure for petitions

for review of such determinations. 14 C.F.R. § 77.1 (2018).

      The regulations state that obstructions are presumed to be airport

hazards unless an aeronautical study determines otherwise.                  Id.

§ 77.15(b). The FAA uses the safety regulations, as well as FAA policy

and guidance materials, to determine whether an obstruction is an
                                     12

airport hazard.    Id.; see also id. § 77.25(c) (noting that obstruction

standards may be supplemented by other guidance).

      The regulations provide certain height safety standards.            The

surfaces used to determine height safety requirements include “an initial

approach segment, a departure area, and a circling approach area,” as

well as “[t]he surface of a takeoff and landing area” of an airport.       Id.

§ 77.17(a). The regulations also establish certain “imaginary surfaces” in

relation to the runways of an airport, which create imaginary arcs within

which an object may be an airport hazard. Id. § 77.19. The size of the

imaginary surface depends upon the type of runway and the types of

approaches a pilot can make on the runway. Id. The arcs are all 150

feet above the airport elevation, and the radius is either 5000 or 10,000

feet depending on the type of runway. Id. § 77.19(a).

      If the FAA conducts an aeronautical study to determine whether an

object is an airport hazard, it will evaluate the following in addition to the

factors set out in 42 U.S.C. § 44718(b)(1),

            (4) Airport traffic capacity of existing public use
      airports and public use airport development plans received
      before the issuance of the final determination;
            (5) Minimum obstacle clearance altitudes, minimum
      instrument flight rules altitudes, approved or planned
      instrument approach procedures, and departure procedures;
              (6) The potential effect on ATC radar, direction finders,
      ATC tower line-of-sight visibility, and physical or
      electromagnetic effects on air navigation, communication
      facilities, and other surveillance systems;
            (7) The aeronautical effects resulting from the
      cumulative impact of a proposed construction or alteration of
      a structure when combined with the effects of other existing
      or proposed structures.

14 C.F.R. § 77.29(a); see also id. § 77.25(b).

      After an aeronautical study, the FAA makes an initial hazard/no-

hazard determination. Id. § 77.31. Pursuant to the regulations,
                                       13
      [a] Determination of No Hazard to Air Navigation will be
      issued when the aeronautical study concludes that the
      proposed construction or alteration will exceed an
      obstruction standard but would not have a substantial
      aeronautical impact to air navigation. A Determination of No
      Hazard to Air Navigation may include the following:
             (1) Conditional provisions of a determination.
            (2) Limitations necessary to minimize potential
      problems, such as the use of temporary construction
      equipment.
             (3) Supplemental notice requirements, when required.
           (4) Marking       and    lighting     recommendations,    as
      appropriate.

Id. § 77.31(d). The no-hazard determination will expire eighteen months

after its effective date. Id. § 77.33(b).

      The regulations provide a procedure to petition the FAA to

reconsider or revise the determination, provided that construction has

not begun and the petition is submitted at least fifteen days before the

determination expires.     Id. § 77.35(a).     This determination will become

final unless the FAA grants discretionary review.            Id. § 77.37, .39

(discussing the procedure for discretionary review).           An individual

seeking discretionary review must do so within thirty days of the date of

the determination. Id. § 77.39(a).

      The no-hazard determination is reviewable as a final agency

disposition. Aircraft Owners & Pilots Ass’n v. FAA, 600 F.2d 965, 966 n.2

(D.C. Cir. 1979). FAA no-hazard determinations have been successfully

challenged under federal judicial review. See, e.g., Town of Barnstable v.

FAA, 659 F.3d 28, 35–36 (D.C. Cir. 2011) (vacating FAA no-hazard

determination for off-shore wind farm); Clark County v. FAA, 522 F.3d

437, 443 (D.C. Cir. 2008) (vacating FAA no-hazard determination for

wind farm near Las Vegas airport).
                                    14

      In Aircraft Owners & Pilots Ass’n, the United States Court of

Appeals for the District of Columbia discussed the limited legal effect of a

hazard/no-hazard determination:

            Once issued, a hazard/no-hazard determination has
      no enforceable legal effect. The FAA is not empowered to
      prohibit or limit proposed construction it deems dangerous
      to air navigation. Nevertheless, the ruling has substantial
      practical impact. The Federal Communications Commission,
      for example, considers the FAA’s classification in granting
      permits for the construction of broadcast towers. The ruling
      may also affect the ability of a sponsor proposing
      construction to acquire insurance or to secure financing.
      Primarily, however, the determination promotes air safety
      through “moral suasion” by encouraging the voluntary
      cooperation of sponsors of potentially hazardous structures.

600 F.2d at 966–67 (footnotes omitted) (citation omitted).

      “Nonetheless, a hazard determination can hinder the project

sponsor in acquiring insurance, securing financing or obtaining approval

from state or local authorities.” BFI Waste Sys. of N. Am., Inc. v. FAA,

293 F.3d 527, 530 (D.C. Cir. 2002); see also White Indus., Inc. v. FAA,

692 F.2d 532, 533 n.1 (8th Cir. 1982) (“Although the FAA determination

has no enforceable legal effect, it does have substantial practical impact

as the Federal Communications Commission considers the determination

in making its decisions with respect to proposed construction.”).

      B. Iowa Law.     The State of Iowa and Carroll County each have

enactments addressing airport hazards.       Any city or county with an

airport may establish an airport commission to manage and control the

airport.   Iowa Code § 330.17(1).    These commissions have “all of the

powers in relation to airports granted to cities and counties under state

law, except powers to sell the airport.”     Id. § 330.21.   These powers

include the authority to make decisions with regard to zoning to prevent

airport hazards. Id. §§ 329.2–.3. “In the event of any conflict between
                                        15

any airport zoning regulations adopted or established under this chapter

and any other regulations applicable to the same area, . . . the more

stringent limitation or requirement shall govern and prevail.” Id. § 329.8.

        The Iowa Code defines an airport hazard as

        any structure or tree or use of land which would exceed the
        federal obstruction standards as contained in 14 C.F.R.
        § 77.21, 77.23 and 77.25 as revised March 4, 1972, and
        which obstruct the air space required for the flight of aircraft
        and landing or take-off at an airport or is otherwise
        hazardous to such landing or taking off of aircraft.

Id. § 329.1(2).

        With regard to airport hazards, section 329.2 states,

               It is hereby found that an airport hazard endangers
        the lives and property of users of the airport and of
        occupants of land and other persons in its vicinity, and also,
        if of the obstruction type, in effect reduces the size of the
        area available for the landing, taking off and maneuvering of
        aircraft, thus tending to destroy or impair the utility of the
        airport and the public investment therein. Accordingly, it is
        hereby declared:
              1. That the creation or establishment of an airport
        hazard is a public nuisance and an injury to the community
        served by the airport in question.
              2. That it is necessary in the interest of public health,
        safety, and general welfare that the creation or
        establishment of airport hazards be prevented.
               3. That this should be accomplished, to the extent
        legally possible, by proper exercise of the police power.
               4. That   the    prevention  of  the   creation   or
        establishment of airport hazards, and the elimination,
        removal, alteration, mitigation, or marking and lighting of
        existing airport hazards are public purposes for which
        municipalities may raise and expend public funds, as an
        incident to the operation of airports, to acquire land or
        property interests therein.

Id.

        If an airport hazard exists, the Commission “may maintain actions

in    equity   to   restrain   and   abate   as   nuisances   the   creation   or
                                     16

establishment of airport hazards appertaining to said airport, in violation

of any zoning regulations adopted or established pursuant to the

provisions of this chapter.”     Id. § 329.5; see also id. § 657.2(8) (“Any

object or structure hereafter erected within one thousand feet of the

limits of any municipal or regularly established airport or landing place,

which may endanger or obstruct aerial navigation, including take-off and

landing, unless such object or structure constitutes a proper use or

enjoyment of the land on which the same is located.”).

      The Code provides a procedure for applying for a variance to zoning

laws. Id. § 329.11. A variance

      shall be allowed where a literal application or enforcement of
      the regulations would result in practical difficulty or
      unnecessary hardship and the relief granted would not be
      contrary to the public interest, but would do substantial
      justice and be in accordance with the spirit of the
      regulations and this chapter; provided, however, that any
      such variance may be allowed subject to any reasonable
      conditions that the board of adjustment may deem necessary
      to effectuate the purposes of this chapter.

Id.

      The Carroll County ordinances state with regard to placement of

towers and antennas, “All tower height allowances outlined in the

preceding sections are subject to approval from the municipal Airport

Commission.”          Carroll   County,   Iowa,    Code   of   Ordinances

§ 14.15.040.02.7 (2017) (emphasis omitted); see also id. § 14.16.010.04

(“All structures with a height greater than 30 feet shall be reviewed by

the Carroll Airport Commission.”).     An applicant for a building permit

must file an application with the county zoning administrator, including

“[d]ocumentation that the proposed tower site and height have been

approved by the appropriate Airport Commission.” Id. § 14.15.040.03.5

(emphasis omitted).
                                    17

      The county board of adjustment, in compliance with Iowa Code

section 355.12, is permitted to hear cases regarding “[v]ariances to

zoning district requirements where there are unusual conditions or

circumstances that cause a hardship when the provisions of zoning are

strictly applied.” Id. § 14.18.010.07.3.

      The board shall reject any such application or appeal that is
      not filed within (10) days of the Zoning Administrator’s
      decision.    Also, the secretary shall reject any such
      application or appeal unless the same are made on
      prescribed forms properly filled out, with all required data
      attached.

Id. § 14.18.010.08.4.

      The airport zoning regulations define an airport hazard as

      any structure or tree or use of land that would exceed the
      Federal obstruction standards as contained in 14 CFR
      77.21, 77.23, and 77.25, and that obstructs the airspace
      required for the flight of aircraft and landing or takeoff at an
      airport or is otherwise hazardous to such landing or taking
      off of aircraft.

Id. § 171.01(3).

      The   county   airport   zoning    regulations   establish   “imaginary

surfaces” as required by the federal regulations, creating a protected

zone encompassing,

             1. Horizontal Zone. The land lying under a horizontal
      plane 150 feet above the established elevations, the
      perimeter of which is constructed by swinging arcs of 10,000
      feet radii from the center of each end of the primary surface
      of Runways 13 and 31, and 5,000 feet for Runways 3 and
      21, and connecting the adjacent arcs by lines tangent to
      those arcs. No structure shall exceed 150 feet above the
      established airport elevation in the horizontal zone, as
      depicted on the Arthur N. Neu Municipal Airport Height
      Zoning Map.

Id. § 171.02(1).
                                     18

      The regulations also state,

            5. Increase in Elevation of Structures. No structure
      shall be erected in the County that raises the published
      minimum descent altitude for an instrument approach to
      any runway, nor shall any structure be erected that causes
      the minimum obstruction clearance altitude or minimum en
      route altitude to be increased on any Federal airway in the
      County.

Id. § 171.02(5).

      A landowner may request a variance from these regulations by

applying to the board of adjustment and submitting a copy of the

application to the Commission.        Id. § 171.05.    The Commission is

permitted to give its opinion on the aeronautical effects of a possible

variance within fifteen days of receiving its copy of the application. Id.

      The airport regulations state, similar to the Iowa Code, that with

regard to conflicting regulations the more stringent requirement prevails:

      Where there exists a conflict between any of the regulations
      or limitations prescribed in this chapter and any other
      regulations applicable to the same area, whether the conflict
      is with respect to height of structures, the use of land, or any
      other matter, the more stringent limitation or requirement
      shall govern and prevail.

Id. § 171.10.

      C. Application of Preemption Principles.          The Danners argue

that the FAA no-hazard determination for their grain leg preempts a

contrary determination by the Commission. The Danners contend that

allowing local airports to determine what constitutes an airport hazard

would impermissibly alter the federal standards. The district court and

court of appeals disagreed and determined that federal law allows for

overlapping local regulation of hazards. We agree that local regulation of

tall structures near flight paths is recognized under federal aviation law.
                                    19

      Under the Supremacy Clause of the United States Constitution,

“the Laws of the United States . . . shall be the supreme Law of the Land

. . . , any Thing in the . . . Laws of any State to the Contrary

notwithstanding.” U.S. Const. art. VI, cl. 2.

      Consideration of issues arising under the Supremacy Clause
      “start[s] with the assumption that the historic police powers
      of the States [are] not to be superseded by . . . Federal Act
      unless that [is] the clear and manifest purpose of Congress.”

Abdullah v. Am. Airlines, Inc., 181 F.3d 363, 366 (3d Cir. 1999)

(alterations in original) (quoting Cipollone v. Liggett Grp., Inc., 505 U.S.

504, 516, 112 S. Ct. 2608, 2617 (1992)).

      [T]he Supremacy Clause has been interpreted to mean that
      even if a state statute is enacted in the execution of
      acknowledged state powers, state laws that “interfere with,
      or are contrary to the laws of Congress” must yield to federal
      law.

Martinez, 896 N.W.2d at 746 (quoting Gibbons v. Ogden, 22 U.S. 1, 211,

9 Wheat. 1, 82 (1824)). The Supremacy Clause is implemented through

the preemption doctrine. Id.

      We have recognized “[t]here is a presumption against preemption

which counsels a narrow construction of preemption provisions.” Huck

v. Wyeth, Inc., 850 N.W.2d 353, 363 (Iowa 2014) (alteration in original)

(quoting Ackerman v. Am. Cyanamid Co., 586 N.W.2d 208, 213 (Iowa

1998)); see also Freeman, 848 N.W.2d at 83 (discussing “cooperative

federalism” under which the federal law sets a floor, not a ceiling, and

states may impose more stringent protections).      That is what we have

here under aviation laws regulating the height of structures in flight

paths, as we explain below.

      There are two broad categories of preemption, express and implied.

Martinez, 896 N.W.2d at 746. Within implied preemption there are two
                                    20

subcategories, conflict preemption and field preemption.      Id.   We will

address express preemption, conflict preemption, and field preemption in

turn.

        1. Express preemption.   “Express preemption occurs when the

federal statutory text clearly provides that congressional authority is

exclusive.”   Id.   Express preemption requires examining the statutory

language to determine the legislature’s intent. Id.

        Although the Aviation Act states that “[t]he United States

Government has exclusive sovereignty of airspace of the United States,”

49 U.S.C. § 40103(a)(1), there is no clear statutory text that Congress

intended to make the FAA’s authority under the Aviation Act exclusive as

to restrictions on structures near airports. We agree with the court of

appeals that the Aviation Act does not expressly preempt the state

statutes and local ordinances at issue here.

        2. Conflict preemption. “Conflict preemption occurs when a state

law conflicts with a federal provision.”   Martinez, 896 N.W.2d at 747.

“Conflict preemption occurs when ‘compliance with both federal and

state regulation is a physical impossibility.’ ”   Id. (quoting Fla. Lime &

Avocado Growers, Inc. v. Paul, 373 U.S. 132, 142–43, 83 S. Ct. 1210,

1217 (1963)).       “Conflict preemption also is imminent whenever two

separate remedies are brought to bear on the same activity.”            Id.

“Conflict preemption also occurs when a state law is an obstacle to the

accomplishment of a federal purpose.” Id. “What is a sufficient obstacle

is a matter of judgment, to be informed by examining the federal statute

as a whole and identifying its purpose and intended effects.” Id. (quoting

Crosby v. Nat’l Foreign Trade Council, 530 U.S. 363, 373, 120 S. Ct.

2288, 2294 (2000)).
                                    21

      The district court concluded that both the federal and local

regulations could be in effect and regulate airport hazards without

conflict. The district court concluded the Aviation Act did not preempt

the local regulations stating,

      The local regulations take a more stringent stance on what a
      hazard is and how it could affect the air space. If the FAA
      regulations contained all airport and safety regulations there
      would be no need for the State to designate zoning powers to
      the Commission.

The court of appeals determined the doctrine of conflict preemption did

not apply because compliance with both statutes was not impossible.

Because the state regulations impose a greater burden, it is possible to

comply with both the state and federal regulations. This is supported,

the court determined, by the statement in the no-hazard determination

that “[t]his determination . . . does not relieve [the Danners] of

compliance responsibilities relating to any law, ordinance, or regulation

by any Federal, State, or local government body.”
      It is possible to comply with the federal, state, and local laws

without conflict. We agree with the district court and court of appeals

that the doctrine of conflict preemption does not apply in this case.

      3. Field preemption. “Field preemption arises when Congress has

enacted a comprehensive scheme.”         Id. at 746.     In cases of field

preemption,

      congressional intent to preempt can be inferred from a
      framework of regulation “so pervasive . . . that Congress left
      no room for the States to supplement it” or where there is a
      “federal interest . . . so dominant that the federal system will
      be assumed to preclude enforcement of state laws on the
      same subject.”

Id. at 746–47 (quoting Rice v. Santa Fe Elevator Corp., 331 U.S. 218, 230,

67 S. Ct. 1146, 1152 (1947)).
                                           22

       “[C]oncluding that Congress intended to occupy the field of air

safety does not end our task.”            Goodspeed Airport LLC v. E. Haddam

Inland Wetlands & Watercourses Comm’n, 634 F.3d 206, 210 (2d Cir.

2011).     “The key question is thus at what point the state regulation

sufficiently interferes with federal regulation that it should be deemed

pre-empted[.]”     Id. at 211 (alteration in original) (quoting Gade v. Nat’l

Solid Wastes Mgmt. Ass’n, 505 U.S. 88, 107, 112 S. Ct. 2374, 2387

(1992)).

       A variety of state and local laws have been preempted by the

Aviation Act, including tort law, 3 state regulation of air travel, 4 and noise

regulations. 5      However, in Goodspeed Airport, the environmental

       3See, e.g., Montalvo v. Spirit Airlines, 508 F.3d 464, 468 (9th Cir. 2007) (holding
that the Aviation Act preempted state law duty-to-warn claims for passengers who
developed deep vein thrombosis on domestic flights); Abdullah, 181 F.3d at 371–72
(holding that air safety standards as they relate to a standard of care for state
negligence claims were preempted); In re Sept. 11 Litig., 811 F. Supp. 2d 883, 891
(S.D.N.Y. 2011) (finding that federal law preempted state law with regard to the
standard of care applicable to the defendant’s conduct in allowing terrorists to hijack
and crash a plane, noting that if state law controlled “air carriers then would be
subjected to an untenable mixture of 50 different state legal regimes, and not to a
uniform federal legal regime”); In re Air Crash Near Clarence Ctr., N.Y., on Feb. 12, 2009,
798 F. Supp. 2d 481, 486 (W.D.N.Y. 2011) (finding that the FAA preempted state law
negligence standard of care). But see Sikkelee v. Precision Airmotive Corp., 822 F.3d
680, 683 (3d Cir. 2016) (holding that the FAA did not preempt design defect claims).
       4See,  e.g., U.S. Airways, Inc. v. O’Donnell, 627 F.3d 1318, 1329 (10th Cir. 2010)
(“Based on the pervasive federal regulations concerning flight attendant and crew
member training and the aviation safety concerns involved when regulating an airline’s
alcoholic beverage service, we conclude that [the state liquor law’s] application to an
airline implicates the field of airline safety that Congress intended federal law to
regulate exclusively. Thus, New Mexico’s regulatory efforts are impliedly preempted.”);
Air Transp. Ass’n of Am., Inc. v. Cuomo, 520 F.3d 218, 219 (2d Cir. 2008) (per curiam)
(finding that federal law preempted a state law establishing a passenger’s bill of rights);
French v. Pan Am Express, Inc., 869 F.2d 1, 1 (1st Cir. 1989) (holding that pilot
regulation statute was preempted).
       5See, e.g., City of Burbank v. Lockheed Air Terminal Inc., 411 U.S. 624, 638–40,
93 S. Ct. 1854, 1862–63 (1973) (concluding that the Aviation Act preempted a city
ordinance attempting to control noise by prohibiting aircraft from taking off between 11
p.m. and 7 a.m.); Burbank-Glendale-Pasadena Airport Auth. v. City of Los Angeles, 979
F.2d 1338, 1341 (9th Cir. 1992) (finding that local regulations regarding airport noise
were preempted).
                                     23

regulation at issue—requiring a permit to cut down trees on wetlands—

was not preempted because it did not sufficiently interfere with the

federal regulations. Id. at 212. The court declined to determine

      whether the FAA Regulations would preempt the state and
      local laws, regulations, and actions challenged here if the
      trees were declared hazards and their removal ordered by the
      FAA. Significantly, in this case the federal government
      renounced any intention—indeed, questioned whether it had
      the authority—to declare the trees hazards and/or order
      their removal.

Id. at 208 n.1.

      Courts have found ample room for state and local regulation. See,

e.g., City of Cleveland v. City of Brook Park, 893 F. Supp. 742, 751 (N.D.

Ohio 1995) (“While it is certainly true that runway placement will have

some tangential effect on flight operations, the question of whether and

where to construct a runway does not substantially affect the use of

airspace. . . . The Federal Aviation Act does not occupy the field of land

use regulations in such a way so as to preempt Brook Park’s

ordinances.”).

      The court of appeals concluded the doctrine of field preemption did

not apply because the Act only sets minimum standards and implies that

another body may lawfully impose more stringent standards. The court

also noted that the FAA did not intend for the no-hazard determination

to supersede state and local law because it has no enforceable legal

effect. We agree for the reasons explained below.

      4. Cases addressing the preemptive effect of FAA no-hazard

determinations for tall structures in flight paths.   We now turn to the

several   cases   specifically   adjudicating   whether   FAA   no-hazard

determinations preempt local regulation of the height of structures in

flight paths.
                                           24

        The Commission relies on Commonwealth v. Rogers, an appeal by a

business owner found guilty of violating a state statute by erecting a

ninety-five-foot-tall sign that encroached on an airport’s approach area,

without seeking prior approval from the Pennsylvania Department of

Transportation.        634 A.2d 245, 246–47 (Pa. Super. Ct. 1993).           The

Rogers court, citing to Aircraft Owners & Pilots Ass’n, concluded that

because FAA hazard/no-hazard determinations had no enforceable legal

effect, the ability to prohibit or limit proposed construction because of

the hazard it poses to air navigation “has been left to the states.” Id. at

250.     The Rogers court concluded, “Thus, although Congress has

concerned itself with the hazards posed by tall structures, it has left

untouched the legal enforcement of standards, which are peculiarly

adapted to local regulation.               Therefore, the states may legislate

concerning such matters.” Id. The court noted that “[b]y enacting [the

state    statute],     the   legislature     empowered   [the   department    of

transportation] to enforce mandatory compliance with FAA regulations

which are designed to identify potential hazards to air navigation.” Id. at

253.    “Unlike the determination made by the FAA, [the department of

transportation’s] determination is enforceable, rather than advisory.” Id.

“In order to ensure that landowners will comply with the requirement of

prior approval by [the department of transportation], the legislature has

mandated that the failure to seek approval is a summary offense.” Id.

The court concluded this was a proper exercise of police power, and “[i]n

this manner, [the department of transportation] can ensure that the

safety regulations promulgated by the FAA are applied uniformly

throughout the Commonwealth to establish a minimum threshold of

safety, irrespective of different standards which may be adopted at the

local level.”    Id.     Rogers is distinguishable, however, because the
                                    25

defendant had not actually received an FAA no-hazard determination as

to the tall sign at issue.

      In La Salle National Bank v. Cook County, a developer sought to

construct eight-story apartment buildings near a naval air base.       340

N.E.2d 79, 81–82 (Ill. App. Ct. 1975). The developer relied on “a letter it

received from the FAA indicating the proposed construction did not

violate the height restrictions imposed by FAA on buildings in military

airport approach zones.” Id. at 83. County zoning officials nevertheless

denied a required zoning reclassification based on local zoning height

restrictions and pilot testimony that the buildings would pose a hazard.

Id. at 81, 83–84.       The appellate court, concluding that the local

standards did not impede aviation, affirmed the rejection of the

developer’s federal preemption claim. Id. at 87–88. Similarly, here, the

Commission’s pilot witnesses testified the grain leg posed a hazard to

aviation.

      The Commission also relies on Aeronautics Commission of Indiana

v. State ex rel. Emmis Broadcasting Corp., 440 N.E.2d 700 (Ind. Ct. App.

1982). There, business owners sought to purchase the assets of a radio

station but wanted to move the broadcast tower.       Id. at 701–02.   The

prospective purchaser was required to coordinate with the Federal

Communications Commission, “vested with authority to regulate the

proposed construction and maintenance of broadcast towers[,]” as well

as the FAA, vested with the authority to determine “whether a proposed

antenna presents a hazard to air navigation.” Id. at 702 & n.2. The FAA

performed an aeronautical study and determined the antenna and tower

would not be a hazard to air navigation.       Id. at 702.   However, the

aeronautics commission advised the purchaser that it must also obtain a

permit pursuant to the Indiana High Structures Safety Act before
                                    26

constructing the tower.    Id.   The aeronautics commission denied the

company’s application for a permit. Id. The Indiana Court of Appeals,

relying on Aircraft Owners & Pilots Ass’n, concluded that state and local

regulations regarding tall structures were not preempted by the Aviation

Act. Id. at 704–06. The court determined that

      Congress has concerned itself with the potential hazards for
      air safety created by tall structures, but it has purposely left
      untouched a distinctive part of the subject—the legal
      enforcement of standards—peculiarly adapted to local
      regulation; thus the state may legislate concerning such
      local matters which Congress could have covered but did
      not.

Id. at 706.

      On the other hand, a federal district court expressly declined to

follow Aeronautics Commission of Indiana and, instead, held that the

FAA’s no-hazard determination as to placement of a broadcast tower

trumped a contrary local regulatory decision. Big Stone Broad., Inc. v.

Lindbloom, 161 F. Supp. 2d 1009, 1021 (D.S.D. 2001).         There, a radio

broadcaster sued members of the South Dakota Aeronautics Commission

(SDAC) for injunctive and declaratory relief, challenging the SDAC’s

denial of a permit to place an 875-foot broadcast tower near a state road
used as a flight path for small aircraft. Id. at 1011–13. The FAA had

issued a no-hazard determination for the tower in that location. Id. The

Big Stone court noted the Indiana Court of Appeals “rooted its rationale”

in the FAA’s lack of power to compel a state regulator to allow

construction of a tower the state deemed hazardous to aviation

“notwithstanding a[n] FAA determination to the contrary.” Id. at 1020–

21. The Big Stone court “craft[ed] a more limited remedy” by enjoining

the SDAC

      from acting to prohibit the construction of proposed
      broadcast towers when the FAA, in adherence to its statutory
                                   27
      and regulatory provisions, determines that the proposed
      tower poses no hazard to air traffic and safety. In essence,
      then, the court enjoins [the SDAC] from vetoing a[n] FAA
      determination of “no hazard” in connection with radio
      broadcast towers.

Id. at 1021. Big Stone has not been followed by other courts. It is also

distinguishable.   Here, we are reviewing a judgment on a bench trial

determining the grain leg is hazardous to aviation and violates local

zoning requirements, rather than a district court ruling accommodating

competing federal and state agency decisions. And, unlike Big Stone, the

Commission was not really “vetoing” the FAA’s no-hazard determination

because the no-hazard letter itself admonished the Danners that they

remained subject to local zoning requirements.

      In Davidson County Broadcasting, Inc. v. Rowan County Board of

Commissioners, the North Carolina Court of Appeals considered whether

a county was preempted from regulating air safety. 649 S.E.2d 904, 907

(N.C. Ct. App. 2007). In that case, a broadcasting company applied for a

conditional use permit to construct a 1350-foot radio tower near a

private airport. Id. at 907–08. After a public hearing, the county board

of commissioners denied the permit, finding that the tower would

penetrate air traffic patterns at the private airport and would constitute

“hazardous safety conditions” in violation of the county zoning code. Id.

The board reached this decision despite a no-hazard determination from

the FAA.   Id.   However, the board noted, “[T]he FAA’s review included

only flight operations to and from public airports.   Miller Airpark is a

private airport to which the FAA regulations do not apply.” Id. at 908.

The court found no conflict between the Act and the county zoning law.

Id. at 911. The court based this conclusion on the language in the no-

hazard letter stating that the no-hazard letter “does not relieve the

sponsor of compliance responsibilities relating to any law, ordinance, or
                                   28

regulation of any Federal, State, or local government body.”    Id.   The

same language is found in the FAA’s no-hazard letter for the Danners’

grain leg.

      On balance, we decline to hold the FAA no-hazard determination

preempted enforcement of local zoning requirements. We reiterate that

“[t]here is a presumption against preemption.” Huck, 850 N.W.2d at 363

(alteration in original) (quoting Ackerman, 586 N.W.2d at 213). Federal

courts recognize that the FAA’s “hazard/no-hazard determination has no

enforceable legal effect” and “[t]he FAA is not empowered to prohibit or

limit proposed construction it deems dangerous to air navigation.”

Aircraft Owners & Pilots Ass’n, 600 F.2d at 966–67. Accordingly, that

role must fall to state and local government, indicating Congress left

room for “cooperative federalism.” See Freeman, 848 N.W.2d at 83. In

our view, the better reasoned authorities discussed above hold state and

local regulators can impose stricter height restrictions on structures in

flight paths notwithstanding an FAA no-hazard determination. Finally,

we rely on the very language of this specific no-hazard determination,

which expressly warned the Danners that they still must comply with

state and local laws.

      D. Whether the District Court’s Injunctive Relief Should Be

Affirmed.     On June 16, 2017, the district court sustained the

Commission’s petition for abatement, finding the grain leg was an airport

hazard constituting a nuisance. The district court ordered the grain leg

to be removed or reconstructed at a lower height. The Danners filed a

motion for judgment notwithstanding the verdict or for new trial, arguing

federal preemption based on our holding in Martinez. The Commission

filed a motion to set a date by which the grain leg had to be removed and
                                       29

to impose a per diem penalty for each day after the deadline the grain leg

continued to stand.

       The court rejected the Danners’ preemption defense based on

Martinez and denied their motion for judgment notwithstanding the

verdict. The court set a May 1, 2018 removal or modification deadline

and, relying on Iowa Code section 329.14, imposed a $200 per day

penalty commencing May 1, 2018, for each day the nuisance continued

to stand unabated.      That penalty has continued to accrue during this

appeal at an annual rate of $73,000. On our de novo review, we affirm

the nuisance determination and remedy except that we vacate the

per diem penalty as inequitable.

       “Permanent injunctive relief is an extraordinary remedy that is

granted only when there is no other way to avoid irreparable harm to the

plaintiff.”   Lewis Invs., Inc. v. City of Iowa City, 703 N.W.2d 180, 185

(Iowa 2005).

       A plaintiff seeking permanent injunctive relief must establish
       “(1) an invasion or threatened invasion of a right; (2) that
       substantial injury or damages will result unless the request
       for an injunction is granted; and (3) that there is no
       adequate legal remedy available.”

City of Okoboji v. Parks, 830 N.W.2d 300, 309 (Iowa 2013) (quoting Cmty.

State Bank, Nat’l Ass’n v. Cmty. State Bank, 758 N.W.2d 520, 528 (Iowa

2008)).

       The court must undertake “a comparative appraisal of all of the

factors in the case,” and consider the following:

       (a) the character of the interest to be protected,
       (b) the relative adequacy to the plaintiff of injunction and of
       other remedies,
       (c) plaintiff’s delay in bringing suit,
       (d) plaintiff’s misconduct,
                                      30
      (e) the relative hardship likely to result to defendant if
      injunction is granted and to plaintiff if it is denied,
      (f) the interests of third persons and of the public, and
      (g) the practicability of framing and enforcing the order or
      judgment.

Helmkamp v. Clark Ready Mix Co., 214 N.W.2d 126, 130 (Iowa 1974)

(quoting Restatement (Second) of Torts, Tentative Draft No. 19, § 936(1)).

      “When determining whether an injunction is the proper remedy,

the court must weigh the relative hardship to each party.”             In re

Langholz, 887 N.W.2d 770, 779 (Iowa 2016).           Courts must structure

permanent injunctions so that it will provide relief to the plaintiff without

“interfer[ing] with the legitimate and proper actions of the person against

whom it is granted.” Id. at 779–80.

      “In equity cases, especially when considering the credibility of

witnesses, [we] give[] weight to the fact findings of the district court, but

[we are] not bound by them.”          Iowa R. App. P. 6.904(3)(g).       The

Commission presented credible opinion testimony from experienced

pilots familiar with the airport.          The district court credited their

testimony that the grain leg poses a hazard to aviation there. So do we.

The other runway would be risky to use in a strong crosswind common

to that location.   The structure is not easy to see in certain weather

conditions. The higher approach requires a steeper descent poorly suited

to some types of aircraft. A distracted pilot might fly into the twelve-story

elevator, with fatal consequences. We affirm the district court’s finding

that the grain leg constitutes a nuisance and hazard to aviation. It is the

$200 daily penalty accruing during this appeal that gives us pause.

      Iowa Code section 329.14 provides, “Each violation of [the airport

zoning] chapter or of any regulations, order, or rules promulgated

pursuant to this chapter, shall constitute a simple misdemeanor and
                                          31

each day a violation continues to exist shall constitute a separate

offense.” The statutory fine for a simple misdemeanor is “at least sixty-

five dollars but not to exceed six hundred twenty-five dollars.”                    Id.

§ 903.1(a).

       Although the district court gave the Danners nine months to abate

the nuisance before commencing the $200 daily penalty, the Danners’

appeal was pending during that grace period. The district court did not

find the Danners in contempt or in willful violation of the court’s

abatement order. The Commission’s case against the Danners was no

slam dunk. It is undisputed that the Danners fully complied with the

FAA directive to paint the structure and place red lights on top. The FAA

adjusted the flight path by 100 vertical feet to accommodate the grain

leg. The FAA determined that these measures alleviated the danger to

aviation posed by the structure. 6 The Commission failed to appeal the

FAA no-hazard determination. Further, despite the trial testimony that

the grain leg poses a hazard, the Commission waited nearly two years to

file this action. The Danners presented uncontroverted testimony that

the cost to remove the grain leg and rebuild it elsewhere is roughly

$450,000 and that it would cost several hundred thousand dollars to
modify the grain leg by reducing its height. We reject as speculative the

testimony that the grain leg will impede efforts to obtain future grants

from    the      same   federal   government       that   deemed      the   structure

nonhazardous, especially since grants of $284,466 and $263,200 were

awarded after the grain leg was built.           We factor these considerations

into our equitable calibration of the postappeal deadline to bring down

the grain leg.

       6Unlike  the district court, we give some evidentiary weight to the determination
by federal aviation authorities that the grain leg is not a hazard to aviation.
                                     32

      The Danners presented a question of first impression in this

jurisdiction as to whether the FAA’s aeronautical study and no-hazard

determination preempted the Commission’s contrary determination that

the grain leg is a hazard to aviation. While the district court, court of

appeals, and now our court declined to give the FAA letter preemptive

effect, this legal issue was not finally resolved until our opinion today.

The caselaw in other jurisdictions is conflicting, and the Danners’

position had some support.       See, e.g., Big Stone, 161 F. Supp. 2d at

1021. We find the Danners pursued this appeal to conclusion based on

their good faith and objectively reasonable belief in their legal position.

      Although we now affirm the district court’s nuisance finding, this

was a fair fight on the merits.      Enforcement of the per diem penalty

under these circumstances would have a chilling effect on a litigant’s

right to appeal a question of first impression in this jurisdiction.      The

Danners exercised their right to appeal, which has now run its course.

We affirm the injunction and hold abatement is required, but conclude it

would be inequitable to impose the $200 daily penalty on the Danners

from May 1, 2018, as originally ordered by the district court until they

abate the nuisance. We elect to vacate the daily $200 penalty accruing

during this appeal. Cf. Iowa Code § 329.4(9) (suspending enforcement

penalties   during     appeal    from     extraterritorial   airport   hazard

determination); Palmer Coll. of Chiropractic v. Iowa Dist. Ct., 412 N.W.2d

617, 622 (Iowa 1987) (holding in contempt proceeding that failure to obey

injunction constituted a single continuous violation and setting aside

daily penalty); see also Ventres v. Goodspeed Airport, LLC, 881 A.2d 937,

968 (Conn. 2005) (affirming order suspending per diem penalties during

pendency of action).
                                   33

      The district court, to its credit, allowed the Danners a nine-month

grace period to abate the nuisance. See Palmer Coll. of Chiropractic, 412

N.W.2d at 622 (commending the district court for allowing time to comply

with its injunction).   We renew this nine-month period from the date

procedendo issues.

      IV. Disposition.

      For the above-stated reasons, we vacate the decision of the court of

appeals, vacate the $200 daily penalty, and affirm the district court

judgment as modified to require the Danners to abate the nuisance

within nine months from the effective date of our opinion.

      DECISION OF COURT OF APPEALS VACATED; DISTRICT

COURT JUDGMENT AFFIRMED AS MODIFIED.

      All justices concur except McDonald, J., who takes no part.
