Tips to Avoid Collisions Between Drones and Helicopters
A Case Study from a Near-midair Collision
The risk of midair collisions between drones and traditional aircraft is always higher at altitudes where both aircraft share the same airspace. The belief that traditional aircraft won’t be flying below 400 feet is a common misconception among drone pilots. Except for takeoff and landing, most fixed-wing aircraft typically operate above 400 feet, but this is not the case with helicopters and agricultural aircraft.
This story features a real-life close encounter between a drone pilot and the crew of an emergency medical helicopter that occurred on April 25, 2022. The account is based upon interviews with the drone pilot, the helicopter pilot, air traffic controllers, and the FAA investigator-in-charge.The sky was clear above El Paso, Texas. At 9:28 a.m. local time, a remote pilot operating under part 107 launched their drone to perform an aerial survey of a high school tennis court on behalf of a construction company. The drone measured 13.2 in. (335 mm) diagonally with a weight of 1.62 lbs. (734 g).
The remote pilot was operating the drone from a sidewalk located at the base of a small hill. The tennis courts were located atop a hill across the street (see figure 1).
From the remote pilot’s location on the sidewalk below, they had the ability to see the drone throughout the entire mission. They were not using a visual observer. The flight took place outside of controlled airspace and airspace authorization was not required.
Figure 2 depicts the location of the remote pilot on the sidewalk at the intersection below the tennis courts (inspection area). This location is at the base of the rising terrain where the tennis courts are located. Additionally, there was rising terrain to the west where a football field is located.
The flight took place in an urban environment with heavy noise pollution. In addition, there are multiple heliports located within a five-mile radius. Just west of the football field is a five-story building obstructing the remote pilot’s view in that direction.
At 9:45 a.m., the drone was operating above the inspection area and climbed to 396 feet above ground level (AGL).
At 9:45 a.m., an emergency medical helicopter was starting up from a helipad located approximately a half mile west of the drone’s survey area. The helicopter was enroute to El Paso International Airport (ELP) with a pilot, nurse, and medic aboard. It initially departed on an easterly heading. It then accelerated to 95 mph and turned northeast-bound, approaching the drone survey area from the west.
At approximately 9:46 a.m., the helicopter passed directly underneath the drone traveling at a speed of 94 mph. The two aircraft were at the same latitude and longitude coordinates with less than 100 feet of vertical separation.
The remote pilot said they heard a helicopter around 14 minutes into their flight. At that point, the drone was at an altitude of 371 feet AGL and 355 feet laterally away from their position.
“I had my drone in sight and proceeded to a stop maneuver to be able to look for the traffic that was behind my line of sight, within approximately 3 seconds, I was able to spot the white and blue helicopter heading on a north-easterly direction at an altitude above my location of approximately of 50 to 100 feet.”
The helicopter pilot said visibility was unlimited with no cloud cover. They were flying eastbound into the sun. In the area where the near-midair collision occurred, there are other hospitals with helipads. They were scanning the other hospitals for any possible arriving or departing rotorcraft and did not see the drone until it was too late to maneuver. The pilot added that the drone did not appear to have illuminated navigation or strobe lights. The pilot noted their climb to cruising altitude was slow but typical for the atmospheric conditions this time of year. Hot temperatures in the summer limit a helicopter’s ability to climb rapidly.
Investigatory Findings
- As part of the drone operation preflight familiarization, the remote pilot did not include the number of nearby heliports or note their locations relative to the operational area of the flight. The remote pilot did not consider the direction and distance to heliports located in the vicinity of the planned operation.
- FAA investigators determined the remote pilot’s location did not afford them with adequate visibility of the surrounding airspace. According to the investigation, there were at least three alternate locations that offered a more adequate view of the surrounding airspace. Part 107 requires a remote pilot to perform an assessment of the operating environment prior to flight. This assessment must consider risks to persons and property in the immediate vicinity, both on the surface and in the air. The assessment assists the remote pilot in selecting a location that ensures adequate visibility of the surrounding airspace at all times during the flight. Adequate visibility of the surrounding airspace provides remote pilots with the opportunity to deconflict from other aviation traffic as required by 14 CFR section 107.37.
- The remote pilot admitted their location prevented them from seeing or hearing the helicopter until it was too late to maneuver out of the way.
- The remote pilot did not use a visual observer to assist in scanning the surrounding airspace for other aviation traffic.
- The remote pilot was focused on viewing the controller display during the operation.
Collision Avoidance Strategies
Raising awareness of the potential for midair collisions between drones and helicopters is the first step toward developing effective mitigation strategies.
☁️ Altitude
Whenever possible, remote pilots are encouraged to fly at the minimum altitudes necessary for the planned operation. Operating at lower altitudes reduces the likelihood of a midair collision. Some aircraft, including helicopters and agricultural aircraft, often fly below 400 feet and routinely share the same airspace as drones.
✨ Flashing Lights
Remote pilots are encouraged to use anti-collision lights during daylight operations. The use of anti-collision lights can aid other pilots in identifying drones.
☑️ Preflight Assessment
As required by regulation, remote pilots must assess the operating environment prior to flight. This assessment must consider the risk to other aircraft in the vicinity of the planned operation. Remote pilots planning flights in urban areas are encouraged to include helipad locations in their preflight planning assessment. Specifically, they should consider the direction and distance of helipads in relation to the operational area of their flight. Remote pilots are reminded that helicopters arriving or departing from helipads routinely operate at low altitudes and speeds in excess of 130 mph.
📍 Location
Identifying the direction and distance of helipads can assist the remote pilot in selecting the best location for the ground control station. This information can assist the remote pilot in selecting the appropriate number and physical location of visual observers needed for the operation.
👀 VLOS
Any effective mitigation strategy for collision avoidance depends upon an understanding of the visual line of sight (VLOS) concept. In each of the collisions between drones and helicopters investigated by the FAA, the helicopter pilots and drone pilots reported not seeing the other aircraft before colliding or seeing them too late to avoid a collision. Each of the drone pilots stated they were flying VLOS and acknowledged their responsibility for yielding to other aircraft.
During their interviews, the drone pilots described VLOS as the ability to see their drone at all times during the flight. However, they failed to explain how they could simultaneously observe the airspace for other aircraft. Visual line of sight aircraft operation is defined in 14 CFR section 107.31 and requires both the ability to see the drone at any time and observe the airspace for other aircraft. Section 107.37 requires the remote pilot to yield the right of way to all aircraft and not create a collision hazard.
According to FAA Advisory Circular 90–48D, Pilots’ Role in Collision Avoidance, on average it takes 12.5 seconds for an undistracted pilot to react to another aircraft. A helicopter traveling at 115 mph covers a half mile in 12.5 seconds. Remote pilots and visual observers are encouraged to ensure they can scan the surrounding airspace to at least half a mile in all directions. Additionally, the view of the surrounding airspace should extend down to the horizon and be free of obstacles or obstructions. If unable, remote pilots should incorporate additional mitigations to their planned operations to ensure an acceptable level of safety.
Watch “The Rotorcraft Collective: Sharing the Airspace with Drones”
This video for helicopter pilots outlines 12 tips for avoiding collisions with drones. It is produced by the FAA Safety Team (FAASTeam) in collaboration with the United States Helicopter Safety Team (USHST), Helicopter Association International (HAI), and the Helicopter Institute in Dallas.
