DJI Mavic Mini Mishap Investigation
In an article written by Jhaveri (2020), he explains the events that unfolded to the eventual crash and loss of his DJI Mavic Mini. Jhaveri, referred to as the operator in this discussion, was planning to fly recreationally to take some footage of the area that he was vacationing in El Nido, Nacpan Beach, which is a double-sided beach with water on two sides of the sand. The plan by the operator was to initially fly the Mavic Mini on a quick flight to determine the best angle for his sunset videography. It is common for photographers to take initial practice shots to ensure their equipment and view are adequate for what they are trying to accomplish.
The operator owned the DJI Mavic Mini fly more combo. The combo provides the operator with three batteries for operations to allow them to change out the batteries for more flights in a short period (DJI, n.d.). The operator decided to use a battery for the flight that was only charged to 35%. This is the first step in the chain of events that led to the eventual crash. The human factors discussion for the battery can fall under the UAS design for the user. The operator chose to fly with a low battery, and the system allows the user to disregard any warnings of a low battery, as seen in Figure 1.
The operator took the aircraft off and hovered above his position. He then noticed that the aircraft was drifting away from him quickly, and he was unable to fly it back to his position. On that day, the winds were gusting to greater than the maximum wind of 17.9 mph (DJI, n.d.). In the event of strong winds, the DJI Fly Application on the operator’s phone will show a red-flagged messaged labeled "Strong Wind Warning," as seen in Figure 2. This is the only indication that the operator will receive regardless of how strong the wind is blowing.
Once the operator noticed that the aircraft was unable to support flight in those conditions he tried to manually engage the Return to Home (RTH) feature to have the aircraft return back to where it took off, however, the Mavic Mini was already flying its maximum ability as it tried to maintain its position with the gusting winds. The aircraft was subsequently lost and crashed into the water.
The Study
For this crash, I elected to perform an independent study of the Mavic Mini to determine what human factors were involved that could have been fixed to help change the outcome of this crash. The first indication was a low battery indication displayed to the user. In Figure 3. I lowered the battery power to 35% to see what the operator would have seen to try and see if there were any indications to change the battery. As seen in Figure 3, the battery indicator is white, and the application shows no warnings to change the battery or that the battery is low.
A normal 100% charged battery for the Mavic Mini can last 30 minutes (DJI, n.d.). In Figure 3, the aircraft is showing that it can fly for 8 minutes and 28 seconds on 35% of power remaining. This is with a wind speed of 7 mph, as seen in Figure 4. Figure 4 shows the local weather at the time and location where I performed the study. With a lower mph, the Mavic Mini will use less power to stay in position as it does not have to fight more than 7 mph of wind compared to the incident.
The application only showed a low battery after the aircraft battery had reached a level of 22%. As seen in Figure 5, the time difference between the 35% in Figure 3 and 22% in Figure 5 is approximately three minutes. After the aircraft reached 22%, the system tried to activate the automated RTH system to land. The system allows the pilot to cancel the RTH and continue flying manually until the aircraft runs out of battery required to continue maintaining flight.
Human Factors
Based on my study of the incident and the research of the DJI system, I believe the control station design has poor human factor design. The system allowed the pilot to fly when the remaining battery would not have allowed for more than a few minutes of flight time before the system's own automated RTH would engage to try and land. The low battery indicator did not emphasize the danger of having such a low battery to the user other than a red flag which the operator admitted to ignoring multiple strong wind warnings with the same red flag “the DJI Fly app pushed a few strong wind warnings, which I casually ignored” (Jhaveri, 2020). With an easily ignored low battery warnings and strong wind warnings contributing to the accident, the operator continued flight without understanding the severity of the situation. A change in the warning indicators to more clearly show the severity of the low battery and strong winds would have potentially saved the aircraft from crashing.
In Figure 6, the Standard Specification for Design, Construction, and Verification of lightweight Unmanned Aircraft Systems Framework explains that critical battery conditions are to be reported. Caution and warnings shall be provided to alert crew members to unsafe operating conditions (ASTM, 2019). This guide shows that DJI meets the minimum requirements of alerting the user, however, I believe this is the difference between what is legal and what is safe. It is a requirement to show the user that the battery is low or the winds are too strong, however, it is unsafe to allow the user to continue flight or in this case, begin the flight with only 35% of battery.
References
ASTM. (2019). Standard Specification for Design, Construction, and Verification of Lightweight Unmanned Aircraft Systems Framework (F3298-10). West Conshohocken, PA: ASTM.
DJI. (n.d.). Mavic Mini - The Everyday FlyCam - DJI. Retrieved May 05, 2020, from https://www.dji.com/mavic-mini?gclid=Cj0KCQjwncT1BRDhARIsAOQF9Lnv7Ccb6HBtp2KFIlo1Tv-N4_JHZZddwWORxNNGx556IPaag2X9HIwaAg7YEALw_wcB
Jhaveri, A. (2020, May 2). I didn't get why some people called the DJI Mavic Mini incapable, until mine flew away. Retrieved from https://www.techradar.com/news/i-didnt-understand-why-people-called-the-dji-mavic-mini-incapable-until-mine-flew-away