In the course of the safety investigation concerning the accident involving the drone SUI-9903 on 9 May 2019 near the city of Zurich (ZH), the Swiss Transportation Safety Investigation Board STSB identified a safety deficit and issued Safety Recommendation SR No. 587 in its final report No. 2390.
SR 590: Measures to ensure that take-off of drones is prevented in unsuitable environmental conditions
| Status | closed |
|---|---|
| STSB assessment | |
| status of implementation | implemented |
| FOCA opinion | |
| Safety deficit | agreement |
| Safety recommendation | agreement |
| next update due | - |
Safety recommendation
Take appropriate organisational or technical measures to ensure that take-off of drones is prevented in unsuitable environmental conditions
Safety deficit
Amendment instructions, controlled flight abortion and sensor technology
Take appropriate organisational or technical measures to ensure that take-off of drones is prevented in unsuitable environmental conditions
The Federal Office of Civil Aviation (FOCA), together with the operator or manufacturer, should take appropriate organisational or technical measures to ensure that take-off is prevented in unsuitable environmental conditions which could lead, for example, to condensation or icing.
Amendment instructions, controlled flight abortion and sensor technology
About one minute after take-off at the University of Zurich (UZH) Irchel, the M2 V9 drone automatically triggered the flight termination system (FTS) and initiated an emergency descent with a parachute. After ejecting the parachute, the connecting rope broke and the drone hit the forest floor without deceleration and was de-stroyed.
As the investigation showed, the applied firmware of the flight controller based on the software version ArduCopter 3.5.0-rc5 was only capable of using two of the three available inertial measurement units (IMU) for the flight control of the drone. As a result, the flight controller's software lacked the ability, known as resilience, not to fail completely in the event of malfunctions or the failure of individual components, but to maintain control of the drone.
Only from software version 3.6.12 onwards was it possible to achieve this resili-ence with the corresponding configuration of the safety-critical parameter ("EK2_IMU_MASK = 7"), as published in a discussion forum of the flight controller manufacturer as Service Bulletin SB 0000002.In the case of the accident involving the largely identical drone SUI-9909 on 25 January 2019 (cf. summary report), the FTS was also immediately triggered due to a loss of the GPS signal. As the investigation showed, the drone's flight attitude was still stable at this time and thus a landing under engine power, either manually controlled on sight or autonomously, would not have been fundamentally impossible.
When operating under extreme climatic conditions, corresponding flight-critical parameters such as ambient temperature and humidity are not included in practice. This would allow a flight mission to be aborted early or not carried out at all under certain conditions.
Implementation and FOCA opinion
15.11.2023 | Response on the status of implementation
29.09.2023 | Initial (and conclusive) statement
09.05.2019 | Unfall mit SUI-9903, bei Zürich (ZH)
In its letter dated 15 November 2023, the Swiss Transportation Safety Investigation Board STSB informs the Federal Office of Civil Aviation FOCA that it has assessed SE No. 590 as "implemented".
Das Bundesamt für Zivilluftfahrt (BAZL) ist mit der Sicherheitsempfehlung (SE) Nr. 590 teilweise einverstanden.In der Bewilligungspraxis des BAZL wird unter anderem auch der Bewältigung von ungünstigen Betriebsbedingungen Rechnung getragen.
Das BAZL richtet sich hierbei nach den Operational Safety Objectives (OSO), wie sie in der Verordnung EU 2019/947 und den dazugehörigen AMC festgehalten werden.
Gemäss dem Schlussbericht Nr. 2390 der SUST waren die Wetterbedingungen zum Zeitpunkt des Unfalls mit den geltenden Beschränkungen für den Betrieb vereinbar und hatten keinen Einfluss auf die Unfallursache. Darüber hinaus ist zu beachten, dass das betroffene UAS-Modell Matternet «M2V9» über die [in OSO #24] geforderten Kriterien hinaus für Flüge in sichtbarer Feuchtigkeit ausgelegt und getestet wurde, um auch signifikanten Wetterbedingungen standzuhalten. Das UAS wurde zudem strengeren Tests unterzogen, als beim «DO-160 Category R waterproofness testing» verlangt wird.
Das BAZL erachtet die Sicherheitsempfehlung Nr. 590 hiermit als vollständig umgesetzt und abgeschlossen.
Last modification 23.01.2025
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