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.
| Status | closed |
|---|---|
| STSB assessment | |
| status of implementation | not implemented |
| FOCA opinion | |
| Safety deficit | agreement |
| Safety recommendation | disagreement |
| next update due | - |
Safety recommendation
Ensure that the drone manufacturer aims to use a redundant propulsion concept
Safety deficit
Ensure that the drone manufacturer aims to use a redundant propulsion concept
The Federal Office of Civil Aviation (FOCA) should ensure that the manufacturer aims to use a redundant propulsion concept – in particular for flights over populated areas – in order to reduce the propulsion-related failure probability due to material wear or exogenous factors such as bird strike.
Redundant propulsion concept for drones
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 landing. After ejecting the parachute, the connecting rope broke and the drone hit the forest floor without deceleration and was destroyed.
In the case of a conventional quadrocopter concept with four propulsion units, as was the case with the M2 V9 drone examined here, a failure of one propulsion unit inevitably leads to a crash or at least to the forced triggering of an automatic flight termination system. Propulsion concepts of drones with 6 or more propulsion units show a significantly lower probability of failure in this respect.
Implementation and FOCA opinion
Current status of implementation
15.11.2023 | Response on the status of implementation
29.09.2023 | Initial (and conclusive) statement
09.05.2019 | Accident SUI-9903, near Zurich (ZH)
The safety recommendation was closed by mutual agreement in December 2024. The FOCA is not planning any further action at present.
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. 591 as "not implemented".
Das Bundesamt für Zivilluftfahrt (BAZL) ist mit der Sicherheitsempfehlung (SE) Nr. 591 nicht einverstanden.
Die Sicherheitsempfehlung, ein redundantes Antriebskonzept zu verwenden, ist ein vereinfachter Ansatz, der die «Common Cause Failures» (Ausfälle aufgrund gemeinsamer Ursache), die Komplexität der Konstruktion eines unbemannten Luftfahrzeuges und die damit verbundenen Wartungsrisiken nicht berücksichtigt. Solche Designempfehlungen stehen im Widerspruch zum risikobasierten Ansatz (SORA), der alle Risikominderungsmassnahmen und das Betriebsprofil berücksichtigt, die in ein SORA einfliessen, welches die Grundlage für die Genehmigung war und heute von der EU-Mitgliedstaatenübernommen wurde.
Zudem werden die Rollen und Verantwortlichkeiten der zuständigen Behörden in der Durchführungsverordnung(EU) 2019/947, bzw. den Applicable Means of Compliance (AMC) 1, Art. 11, Abs. 1.5 (f),festgelegt:
According to Regulation (EU) 2018/1139 (the EASA ‘Basic Regulation’), EASA is the authoritycompetent in the European Union to verify compliance of the UAS design and its components withthe applicable rules, while the authority that is designated by the Member State is competent toverify compliance with the operational requirements and compliance of the personnel’s competencywith those rules
Dementsprechend ist für die Überwachung der Regelkonformität bezüglich Konstruktion (design) undAufrechterhaltung der Lufttüchtigkeit (continuous airworthiness) die Agentur der Europäischen Union für Flugsicherheit (EASA) die zuständige Behörde.
Die Umsetzung der Sicherheitsempfehlung ist aus Sicht des BAZL aufgrund der genannten Ausführungen nicht praktikabel und entgegen den geltenden Vorschriften, deren unilaterale Änderung nicht möglich ist. Das BAZL erachtet die Sicherheitsempfehlung Nr. 591 in Bezug auf sein Amt als erledigt.
Last modification 23.01.2025
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