Drone Manufacturer: DJI
Drone Model: Mavic 2 Pro
Country: United States of America
Pilot Qualifications: Licensed or Certificated by Aviation Authority
Pilot Flight Experience: 31.3 Hours
Link to External Information About This submission:
File Uploaded: default
During a late-day flight on the northern Sumner WA fires site.
6 minutes into a programmed mapping flight with drone deploy, a helicopter was heard approaching the flight position from the south. Once I turned around, the unmarked helo was approaching in a diagonal position flying along the powerlines with a camera or other sensor pointed out the side of the aircraft. I used the pause function in Drone Deploy and watched while the helo continued north then circled one of the towers and continued north. The position of the paused Mavic was only a few hundred feet from the likely flight path, at a higher altitude than the helo at the time (helo 150ft, Mavic 500ft).
Instead of leaving the unit to hover, and allow the helo to close in, I pushed the return to home option and watched the Mavic stats to see how quickly it was returning and at what level. The programmed return altitude was 450ft and the Mavic was returning at 33mph, and at an angle that I estimated would get too close to the helo flight path, so I switched to manual mode in drone deploy and used the left elevation control to force the Mavic into a downward angle to loose altitude continuing on the same return path with the forward stick toward the home location.
While bringing the Mavic downward and homeward, watching the stats on the controller, I was also focused on the continued movements of the helo while it appeared to be inspecting the towers, and moving northward into the programmed flight area.
On the Mavic return, it reached a low enough altitude, and was on an unfortunate course, to collide with the upper structure of a mud separating plant tank on the southern end of the site. The impact location was approximately 60ft above the ground and 218ft from the home location based on telemetry from the controller and data from the flight app.
I used that info to search the site, to conduct a 20-minute search for the bright orange Mavic but found no sign of it. I then asked one property owner and one employee to help search the upper structure if possible due to a locked access ladder, and they were happy to help. From there search, plus a short flight with another drone to aid the search, we concluded that the drone likely fell into the primary or secondary open-topped mud tanks, and would not be recoverable.
Pilot Reported Cause
Controlled Airspace (fire TFR) incursion (without incident command contact) caused emergency drone avoidance response that prioritized manned helo safety over drone safety. A singularly tall obstruction was struck while on direct return to the home position. The pilot was visually focused on the helo movement and not specific drone return path obstacles. No people on site due to fire evacuations. An observer was not available at the time due to limited staffing.
First off, I would like to applaud the pilot that submitted this report. Every incident or accident is an opportunity for us all to learn. I’m going to point out some issues and suggestions but these are done only in an effort to help all pilots, not chastize this pilot.
Since there are so many issues with this flight I would recommend that all pilots that have a similar episode file an anonymous report with the Aviation Safety Reporting System to get some immunity from regulatory actions.
Helicopter Radio Communications
I am a big advocate of UAS pilots that operate in areas that helicopters may be more likely to operate in, to carry a VHF aviation radio transmitter.
These incidents would be public safety incidents where helicopters may be participating, news helicopters may be present, or legitimate accessory aircraft may be operating.
I have a free class I created – Aviation Radio Communications for UAS Public Safety Pilots.
The pilot in this report correctly used his ears and noticed a helicopter was entering the area. A handheld VHF radio, as I describe in the class, has a range of a few miles. By at least attempting to contact the helicopter pilot of the frequency I describe in the class, he could have quickly worked out an air deconfliction solution.
Helicopter Target Vision
I can assure you as a public safety pilot, when myself, or any manned pilot, is flying at a low-altitude we get tunnel vision. The primary focus is what is ahead of the aircraft that we might collide with. We are not looking for drones. There is just no time. It is likely the helicopter pilot was fixated on the powerlines and flying a profile that accomplished the mission and would not have been expecting to see a drone flying in that area.
Return to Home Height
The pilot reported the RTH altitude was set to 450 feet and appears to state the Mavic was operating at 500 feet. As the FAA says, “The maximum allowable altitude is 400 feet above the ground, higher if your drone remains within 400 feet of a structure. Maximum speed is 100 mph (87 knots).”
Drones have to give way to all other operating aircraft, “Each small unmanned aircraft must yield the right of way to all aircraft, airborne vehicles, and launch and reentry vehicles.” – Source
Any UAS flight outside of the visual line of sight creates an imminent safety hazard when even operating below the maximum height of 400 feet. Helicopters can operate at any altitude and in the airplane I can fly as low as I feel is safe in a “sparsely populated area.” The limitation for me in the airplane is “the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.”
In the case of a search and rescue or natural disaster assessment, there have been times when I have been over water or “sparsely populated areas” that the situation required flight below 500 feet AGL.
Drones do not own the airspace below 400 feet. They have a right to operate in that space, as long as there are no airspace restrictions.
Even as a manned airplane pilot I have to always bee on the lookout for other aircraft in disaster areas.
Here is a picture of me passing within a few hundred feet of a helicopter traveling in the other direction.
The helicopter is hard to spot because of all the ground clutter beneath it. Spotting a drone is darn near impossible. It is much easier to locate things above you when you are standing on the ground with the sky above. This is one of the issues the helicopter pilots talk about in the class.
Final Termination Point
The Mavic was operating near aircraft and FAR 107.37 deals with this issue. While the UAS pilot was attempting to move the Mavic out of the way, they seemed to overlook two other possible solutions that might have made the situation safer.
- Land the drone at the point it was at rather than attempting to return.
- We can’t ever forget that we should always be willing to crash the drone in the event it creates a safety hazard. All pilots should mentally prepare before the flight that a Final Termination Point must always be kept in mind. As John Walkie from FDNY said, “Start every mission with a termination point. What is a termination point? This is the place you intend to crash as a last resort. I know it sounds counterproductive, but if you can’t bring the aircraft back safely, this is where you plan to crash it.” He added, “The termination point is the final straw, the last hoorah, the last-ditch effort to safely bring the craft to the ground. This is the area you plan to walk to and pick up the pieces… not recover an intact sUAS (if that’s the case, you are indeed fortunate).”
Temporary Flight Restriction Incursion
If you are operating in a fire TFR no flight is permitted without coordination.
Here is an example of a current wildfire TFR notice.
Drone flight may be permitted within a TFR but it must be coordinated with the authority responsible for the airspace. Every drone pilot should be looking up active TFRs before a flight. Keep in mind there are many reasons why TFRs exist that are not is disaster areas. A TFR may be issued for things like model rocketry, sporting event, VIP visit, etc. Do not assume a TFR does not exist in your area if there is not an ongoing natural disaster.
As you can see in the photo provided, the landing zone (LZ) location is not optimal. In my opinion, it is located far too close to structures on the ground and it appears more open areas were available close by. It is not clear if this LZ was established for the attempted recovery flight but regardless, the LZ is in a position that unnecessarily limits options. This is a lesson learned by the pilot in this report.
Using the UK DROPS Calculator we can see that at the estimated collision height of 60 feet and with an aircraft weight of 907 grams, the DROPS calculator states if the aircraft had fallen from that altitude and struck someone wearing a hard hat it could have been fatal.
Every accident is a chain of events and our education about Aeronautical Decision Making is supposed to help us recognize issues and take the correct action.
In this accident, hindsight may be unfair but looking back, the flight should never have occurred in a TFR. If helicopters might be expected to be operating, a handheld VHF radio and knowledge of how to use it properly would have been helpful. The UAS should never have been outside VLOS given the fire disaster. And an awareness that manned aircraft might be operating at any altitude and may be more likely to given the TFR.
In my opinion, the flight should just have never happened. But there is no sense wasting an opportunity to learn and I’m sure our hero pilot that submitted the report learned a lot from this.