It goes without saying that both drones and crop dusters perform valuable services for agriculture. The only problem is that they share common low-altitude airspace -- with the potential for disastrous consequences. To head off this problem, Agribotix has been working with the Colorado Agricultural Aviation Association (CAAA) during the 2015 growing season to devise ways of de-conflicting the airspace.
The first step was to determine if the traditional aviation see-and-avoid strategies are effective in avoiding mid-air collisions. To do this, Jessica Freeman, the executive director of CAAA, arranged a flight test as part of the CAAA S.A.F.E. Fly-in at the La Junta airport on October 1 and 2, 2015. Five manned aircraft – four fixed-wing crop dusters and one Robinson R44 helicopter – participated and two Agribotix Enduro quadcopters served as the bogeys. Jessica selected five fields in the vicinity of the airport for testing. The pilots were told that drones may - or may not -- be in Fields A to C. Fields D and E contained ground markers for testing.
Deliberately putting manned aircraft and drones in the same airspace carries some risk. To make the event as safe as possible, three certificated pilots -- Greg Griffit of Avian LLC, Constantin Diehl of UAS Colorado, and Ben Marcus of AirMap – carefully constructed the test plan. The manned aircraft were directed to perform a “clearing pass” circle around the edge of the field at 250ft AGL while the drone airspace was either at 100ft or 400ft AGL in the center of the field. The manned pilots departed the La Junta airport at 30-minute intervals. They then waited at rally points outside each field until given clearance to enter by the safety officers on the ground. If anyone on the ground or in the air indicated a safety issue there was a preplanned “knock it off” maneuver in the test plan that would be executed immediately.
When/if the manned aircraft spotted the drone, they would indicate so on their radio and emit a burst with their smoke generator. They were to call out “No Joy” if no drone was spotted.
The testing began at 8:30 in the morning. Field A was used as a control with no drone. Tom McKinnon of Agribotix was flying an Enduro in Field B and Jimmy Underhill, also of Agribotix, flew his Enduro in Field C.
The first crop duster zoomed overhead into Field B at well over 100mph and nearly took my breath away. The pilot made his circle but “No Joy” was the report. Thirty minutes later we had the same result from the next aircraft. The third crop duster gave us a satisfying smoke trail indicating a visual contact. Up next, the R44 rotorcraft also spotted the Enduro but its airspeed was much lower than the fixed-wing aircraft and the copter had a crew of two on board. Finally, “No Joy” from the last aircraft. Jimmy had similar results from Field C except not one of the fixed-wing aircraft spotted his Enduro.
In the pilot debriefing, the one fixed-wing spotting was due to a lucky sun glint off the quadcopter. The helicopter crew reported that although they saw they Enduros they had difficulty tracking them (and we were traveling at half our normal 20 knot speed).
Fields D and E had some tarps placed to indicate UAV operations. The orange one supplied by Agribotix was the most visible from the air but it turns out that this color of orange is also the type of tarp used by farmers to dam their irrigation ditches. For any future tests we’ll use a fluorescent color.
The test results are still being analyzed, but there are some early conclusions we can make.
1. See-and-avoid is a terrible strategy for keeping low-altitude airspace safe. Both parties – crop dusters and drone operators – MUST work actively to devise a solution to ensure that the two aircraft types are never in the same airspace at the same time. Fortunately CAAA and the Colorado UAV community are doing just that.
2. Audible warning of a crop duster’s approach is also a terrible strategy. On Thursday we observed crop duster training at the airport. We could clearly see the crop dusters making their low-altitude approach (10 to 15 feet AGL!) at well over a quarter mile, but we didn’t hear them until they were a few hundred yards away. This would give the UAV operator only a few seconds to respond.
3. Communication is key. AirMap, a software product that allows low-altitude airspace users to declare in advance their zones of operation, was demonstrated by Ben Marcus, the AirMap CEO. This product is simple to use and can be very effective if it is adopted by all parties. We look forward to wide support of AirMap by the community.
4. Technology might help. Potentially ADS-B could be the solution but it will be many years before the crop-dusting community adopts it. Both cost and weight need to drop before UAVs widely accept ADS-B.
5. Ground markers are an OK backstop. Crop dusters fly a clearing pass around a field before they spray. If a universally accepted ground marking system, similar to the prototypes tested out in La Junta, were adopted then the manned aircraft would be warned. However, in our opinion, this should not be the primary means of warning manned aircraft.