by Olivia Hanson, Associate Editor, Center for Transportation Studies
According to federal regulations, keeping the airspace around an airport clear of obstructions is essential for safe flight operations.
MnDOT Aeronautics aviation representative Rob Mason explained during a recent AirTAP webinar how to identify and address obstructions before they affect safety or possibly limit operations.
Federal aviation regulations (FAR Part 77) define an obstruction as any object that penetrates protected airspace around a runway. These protected areas, known as imaginary surfaces, ensure aircraft have adequate clearance. Trees, buildings, crops, vehicles, and terrain can all become obstructions if they extend into those imaginary surfaces.
MnDOT inspects Minnesota’s public airports on a three-year cycle using the FAA Form 5010 Airport Master Record process. MnDOT staff use laser rangefinders, global navigation satellite system devices, and cameras to measure potential obstructions. The 5010 report indicates a confirmed obstruction in red and objects that are almost an obstruction in yellow.
Mason said airports should not wait for their 5010 inspections to identify obstructions or potential hazards. Approach, primary, and transitional airspace surfaces are most likely to have issues with obstructions. For approach surfaces, trees and brush often cause concerns.
Seasonal crops and nearby roadways also can create obstructions. Crops planted too close to the pavement, tall grass, stored equipment, and parked vehicles often are obstructions on primary surfaces.
While MnDOT focuses mainly on approach and primary surfaces, transitional obstructions can still affect circling procedures and helicopter operations. If obstructions remain, the FAA could restrict or cancel approach procedures, raise minimum descent altitudes, add operational restrictions, or issue objectionable determinations.
“At the end of the day, we want our airports to be accessible. We want pilots to be able to use them in most types of weather conditions,” Mason said. “However, they're limited by the approach that's given. If that approach does not allow flight on that particular day because circling is not authorized or it's not authorized at night due to obstructions, that's business the airport is not going to receive.”
Mason encouraged proactive planning and communication, particularly with neighboring landowners. Removing vegetation typically is the preferred solution. When removal is not possible, marking and lighting may be a good alternative.
Mason also emphasized the importance of partnership. “We want to be your partner in identifying these obstructions before they are brought to your attention on a 5010,” Mason said.
Obstruction management is ongoing work. Trees grow, crops change, and land use often evolves. By regularly monitoring possible obstructions, airports can maintain compliance and preserve their operational flexibility. Maintaining clear airspace is a critical element of airport accessibility.
Sessions on airport safety, including obstructions, will be highlighted during the upcoming Minnesota Airports Conference, which will be held in Nisswa from April 22–24, 2026.
