One of the hardest things to tell farmers is that they can’t plant crops on perfectly good tillable land. Yet that can happen when crops encroach on the land surrounding an airport.
As part of MnDOT’s 5010 airport inspections, MnDOT Aeronautics inspectors identify any objects obstructing the navigable airspace surrounding an airport as defined in FAA Regulations Part 77. Typically, these obstructions are trees, brush, the occasional fence—and sometimes even crops planted inside the clear zone surrounding the runways. Depending on the airport, the land inside the clear zone can either be owned by the airport and leased to a farmer or privately owned.
Photos: Jared Wedel
To understand what’s required by Part 77, we must first understand how the FAA defines the imaginary surfaces around a runway that must be kept clear.
Primary surfaces are clear zones that surround any runway. The primary surface varies depending on the runway and type of approach. According to 14 CFR 77.19–Civil airport imaginary surfaces, the primary surface is centered on the runway. The primary surface runs the length of the runway for turf runways and extends 200 feet off each end for paved runways.
The width of the primary surface varies as well. The minimum width is 250 feet centered on the runway (125 feet on either side of the centerline). If either end of the runway has an instrument approach, the primary surface is 500 feet wide. It is further widened to 1,000 feet for runways with a precision approach or non-precision approaches with visibility minimums less than 3/4 of a mile. The only things allowed inside the primary surface are objects required for airport operations, such as airport signs and runway lights.
The approach surface is the second imaginary surface defined and regulated under 14 CFR 77.19. The approach surface is meant to keep a clear flight path in the airspace used for landings and takeoffs. Approach surfaces extend uniformly upward and outward from the primary surface at a slope of 20:1, 34:1, or 50:1, depending on the type of approach for the runway.
Guidelines help communicate clear zones
MnDOT has created guidance to help clarify the boundaries that must be maintained around an airport to ensure a safe and unobstructed airspace. Airport managers are encouraged to use these guidelines, several of which are described in the following paragraphs, to talk with local farmers prior to each planting season.
Primary surface. Within the primary surface, there should be no farming of any kind within 125 feet of the runway centerline; rather, this area should be kept as a grassy clear zone maintained by the airport. This clear zone for aircraft will improve safety, minimize damage, and allow emergency services to access aircraft quickly.
From 125 feet to the outer boundary of the primary surface, low crops such as soybeans and peas, and cereal grains such as alfalfa, wheat, barley, and oats with mature heights of less than four feet, can be planted. Hay is another suitable crop for this area, but as the hay is baled, the bales must be immediately moved to outside of the primary surface to prevent obstruction. If the runway has an ILS approach, that 125 feet increases to 250 feet from the centerline to avoid interfering with the localizer signal.
Approach surface. For the approach surface, crops should be planted no closer than 200 feet from the end of the runway for a turf runway and 400 feet for a smaller paved runway. For runways with non-precision approaches that can land aircraft over 12,500 pounds, that number is 600 feet. For runways with precision approaches, no crops can be planted within 700 feet of the end of the runway.
Clearances around airport navigational aids like ILS antennas, VORs, and automated weather stations are also specified in MnDOT’s guidance.
The illustrations in Fig. 1 can help communicate where the primary and approach surfaces are located. Following these guidelines requires constant attention and monitoring by airport managers. For example, drainage concerns may arise from the cropland surrounding an airport. Wildlife often accompany crops, so that’s another potential issue to address. The operation of large farm equipment around the airport also requires effective communication between the farmer and the airport; if necessary, the airport should issue a NOTAM to notify pilots of any risk.
When it comes down to it, care must be taken to effectively communicate with neighboring farmers, landowners, and those operating on farmland surrounding an airport to ensure that these operations do not interfere with safe aircraft operations.
More information about MnDOT’s agricultural operations guidelines can be found on the Aeronautics website.
—Jared Wedel is the North Region Airport Coordinator with MnDOT Aeronautics.
