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DJI Cadence remote controller and the DJI Inspire 2 unmanned aircraft without payload (Source: djicdn.com)
DJI Cadence remote controller and the DJI Inspire 2 unmanned aircraft without payload (Source: djicdn.com)

Fly-away after compass malfunction

Status : Closed

On 11 April 2020 the crew of a DJI Inspire 2 Unmanned Aircraft System (UAS) conducted a crowd observation and crowd control mission in the Zuiderpark, The Hague. Shortly after take-off, during post take-off checks, the pilot lost control over the Unmanned Aircraft (UA). After the loss of control, a fly-away occurred. While the pilot tried to regain control, the UA flew over a line of trees, blocking the line-of-sight between the Remote Controller (RC) and the UA, after which the connection with it was lost. Thereafter, the UA flew uncontrolled over the city of The Hague. After about 18 minutes of flight, the UA initiated an automated landing sequence due to low battery voltage, but was unable to complete it. The aircraft hovered until insufficient power was left and subsequently crashed in an urban area on a sidewalk.

Fly-away after compass malfunction

Shortly after take-off, the Unmanned Aircraft (UA) did not consistently respond to pilot input and eventually became uncontrollable due to an incorrectly calibrated compass. On the prior flight, a loudspeaker payload was used. This payload differed from the camera payload on the incident flight. During preparation of the incident flight, the Unmanned Aircraft System (UAS) software did not show a compass calibration warning and therefore the pilots did not recalibrate the compass.

The operator did not have procedures for compass calibration in relation to payload changes and relied on indications from the software. By doing so, the operator complied with the UAS manufacturer’s recommendation, which stresses to only calibrate the compass when indicated by the software. This investigation shows that the software is not able to detect an incorrectly calibrated compass in all cases. Therefore, it is advisable to manually start a compass calibration after a payload change, to prevent an unwanted compass offset that may lead to a loss of control.

After the loss of control, the pilot switched to the Return-To-Home (RTH) flight mode. This was in line with the operator’s procedures and the UAS manufacturer’s guidelines. However, the RTH flight mode also depends on the compass. Therefore, in some cases switching to the A(ttitude)-mode should be given priority because it eliminates the dependence on the compass. Switching to A-mode is advisable if the crew is unsure whether there is a compass malfunction because RTH still works when flying in A-mode.

This investigation shows that there are risks associated with using (different) payload. It is therefore important that users know those risks and take extra care when using different types of payload.

Recommendations

To conduct Unmanned Aircraft System (UAS) flights, it is important that the operator and pilots have access to up-to-date information about the UAS, the (functioning of) onboard systems, payload and recommended procedures and safety guidelines. In that respect, operators and private users largely rely on the manufacturer’s best practices when using UAS.

The manufacturer has published manuals and safety guidelines for the UAS. Although the average life span of a UAS is shorter than that of a regular aircraft, UAS can be in use for many years, even after production has ceased. It therefore remains important to update the guidelines using the latest safety insights, in such that users always have access to up-to-date information about the safe use of their UAS and the risks of flying with it.

To improve the safety of the use of UAS, the Dutch Safety Board issues the following recommendation:

To Da-Jiang Innovations Science and Technology Co., Ltd. (DJI):

1. Review the UAS user manual and safety guidelines using the safety lessons learned from this incident, and clarify the following aspects:

a. actions in the event of controllability issues and when to use the RTH and A(ttitude)-mode;

b. in which cases the compass must be calibrated;

c. the risks associated with flying with (different) payload types.

To learn from accidents and incidents and to prevent them from happening again, it is vital that all parties involved, such as state safety investigation authorities and UAS operators, have access to the relevant information. In this regard, manufacturer support is essential.

Manufacturers have a responsibility with regard to the quality and safety of a product. In the area of cooperation with regard to safety investigations, the Board sees room for improvement on the part of the manufacturer, both towards the safety investigation authorities and operators.

Therefore, the Dutch Safety Board issues the following recommendation:

To Da-Jiang Innovations Science and Technology Co., Ltd. (DJI):

2. Ensure that safety investigation authorities and operators are timely provided with technical support and relevant information for the purpose of safety investigation regarding UAS manufactured by DJI.

Deliberations with safety investigation authorities from other states have revealed that the abovementioned issue is not unique to the Netherlands. Therefore, in addition to the recommendation, the Dutch Safety Board will continue to stimulate discussion on this topic with other safety investigation authorities, emphasising the importance of manufacturer participation in safety investigations in the appropriate international bodies, in particular the International Civil Aviation Organization (ICAO).

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