Aviation safety issues and actions

No consideration of transient control loads in the design standard

Issue number: AO-2014-032-SI-05
Who it affects: All operators of ATR 42 and ATR 72 aircraft
Issue owner: European Aviation Safety Agency (EASA)
Transport function: Aviation: Air transport
Background: Investigation Report AO-2014-032
Issue release date: 24 May 2019
Current issue status: Safety action pending

Safety issue description

The design standard for large transport aircraft, Joint Aviation Requirements - Part 25 (JAR-25), did not require that the demonstrated potential for flexibility in the control system to develop transient dynamic loads, be considered during certification. Similarly, the current certification standard for Large Aeroplanes (CS-25) does not address this issue.

Proactive Action

Action number: AO-2014-032-NSA-053
Action organisation: European Aviation Safety Agency (EASA)
Date: 24 May 2019
Action status: Monitor

On 11 January 2019, the ATSB was informed by EASA that the proposed amendments to CS-25 contained in Notice of Proposed Amendment (NPA) 2014-02 would address this safety issue. Review of the NPA by the ATSB identified that the proposed changes to the Acceptable Means of Compliance (AMC) 25.671, contained in Book 2 of CS‑25 included consideration of transient responses (AMC 25.671 9.e.1.(ii)). The changes also include that the structural substantiation of control system failures, specifically for jam conditions (AMC 25.671 9.e.2.(ii)), should be based upon a flexible aircraft model (AMC 25.671 9.e.2.(iii)).

The Comment-Response Document (CRD) relating to NPA 2014-02 indicates that the work on this NPA commenced on 18 March 2013. The CRD also notes that, as of 5 September 2018, the decision on adoption of the NPA is due in the second quarter of 2019.

ATSB comment:

The ATSB acknowledges the efforts of EASA to address this safety action and that this work was commenced prior to the VH-FVR occurrence. The ATSB accepts that the amendments would provide sufficient information to reduce the risk of the transient effects of future pitch disconnect/uncoupling designs. However, the ATSB notes that these amendments have not yet been incorporated in to the certification standard, so will monitor the situation until those amendments have been taken.

Last update 24 May 2019