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Inadvertent activation of the elevator control system - pitch uncoupling mechanism

Issue number: AO-2014-032-SI-01
Who it affects: All operators of ATR 42 and ATR 72 aircraft
Issue owner: ATR
Operation affected: Aviation: Air transport
Background: Investigation Report AO-2014-032
Date: 15 June 2016

Safety issue description

Inadvertent application of opposing pitch control inputs by flight crew can activate the pitch uncoupling mechanism which, in certain high-energy situations, can result in catastrophic damage to the aircraft structure before crews are able to react.

Background to the safety issue

Initially, the ATSB was unaware of any other in-flight pitch disconnect occurrences on the ATR 42/72 series aircraft. As a result, the existing procedural risk controls were considered effective at maintaining a sufficiently low probability of a recurrence of the occurrence involving VH-FVR on 20 February 2014. As such, the ATSB did not initially consider that immediate safety action was necessary.

However, once aware of other in-flight pitch disconnect occurrences, none of which were because of a jammed system, it became apparent that the related procedural risk controls were not sufficiently effective. The likelihood of an inadvertent in-flight pitch disconnect has been demonstrated to be higher than the initial assessment suggested.

Proactive Action

Action organisation: ATR-Gie Avions de Transport Régional
Date: 15 June 2016
Action status: Released

Proactive safety action by ATR

As a result of this occurrence and a briefing from the ATSB on 5 February 2016 on the safety issue, ATR released an All Operators Message (AOM). The message informed operators of ATR 42/72 aircraft of revised maintenance and operational documentation relating to the pitch control system and pitch disconnect occurrences as follows:

ATR 42/72 aircraft of revised maintenance and operational documentation relating to the pitch control system and pitch disconnect occurrences

Proactive Action

Action organisation: Virgin Australia Regional Airlines and Virgin Australia Airlines
Date: 15 June 2016
Action status: Released

Proactive safety action by Virgin Australia Regional Airlines and Virgin Australia Airlines[19]

Virgin Australia Airlines advised that, in response to this occurrence, they had taken action to reduce the potential for pitch disconnects and to manage the risk of adverse outcomes from such occurrences. These included:

  • reviewing and revising (where necessary) policy and procedures associated with descent speeds, handover and takeover procedures, overspeed recovery and on ground pitch disconnects
  • incorporation of a number of factors surrounding the event into training material and simulator checks
  • improved pilot awareness through Flight Crew Operations Notices, manufacturer’s communications (All Operators Messages) and ongoing training and checking
  • updated maintenance requirements following a pitch disconnect.

__________

  1. Since the pitch disconnect occurrence, Virgin Australia Airlines had taken over operation of the ATR 72 fleet from VARA.

Proactive Action

Action organisation: Toll Aviation and Toll Aviation Engineering
Date: 15 June 2016
Action status: Released

Proactive safety action by Toll Aviation and Toll Aviation Engineering

Toll Aviation and Toll Aviation Engineering advised that, as a result of this occurrence, they issued a safety alert to their flight crew and aviation maintenance engineers. This alert advised that, in the event of a pitch disconnect, the aircraft was to be grounded until the appropriate checks had been carried out.

 
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Last update 05 May 2017