The design of the ATR 72 pitch control system resulted in limited tactile feedback between the left and right control columns, reducing the ability of one pilot to detect that the other pilot is making control inputs. In addition, there were no visual or auditory systems to indicate dual control inputs.
In their response of 26 June 2019, ATR did not provide any new and compelling evidence to indicate that the risk of this safety issue had changed. Again, they were focussing the attention on crew resource management, which may reduce the probability, but has not been shown to prevent dual control inputs. ATR has not provided any further updates or responses to indicate that any further work to mitigate the identified risk has been taken. As such, the ATSB has decided to close this safety issue as not addressed.
The ATSB recommends that ATR assess the operational risk associated with limited tactile feedback between left and right control columns in the context of no visual or auditory systems to indicate dual control inputs.
Regarding the ATSB statement on limited tactile feedback, ATR would like to recall that the movement of the control column of the pilot monitoring mirrors the control column movement of the pilot flying. It thus provides visual information to the pilot monitoring.
Then, if the pilot monitoring applies an uncoordinated input, he/she will experience an unusual effort, either heavier or lighter but not as expected due to the combination of the effort associated with the usual aerodynamic loads and of the effort applied by the other pilot.
As per ATR AOM42/72/2016/03, a prolonged and inappropriate application of dual opposite control column inputs at high speed leading to pitch disconnection may cause significant structural damage and should be avoided as per CRM (Crew Resources Management).
The purpose of the pitch disconnect warning system is to alert the crew that the two elevators are disconnected and that operational procedures have to be applied as per the AFM/FCOM.
With regards to the risk associated to dual inputs, the following actions have been taken at various industry levels in order to prevent occurrence:
With all the taken actions, ATR considers that the Safety Recommendation AO-2014-032-SR-057 is addressed.
The ATSB acknowledges the progress made in response to the recommendation.
On 26 June 2019, ATR stated that 'ATR considers that the Safety Recommendation AO-2014-032-SR-057 is addressed.' There have been no updates or responses from ATR regarding this Safety Recommendation since June 2019.
The ATSB has considered the response from ATR on 26 June 2019 and make the following comment:
The ATSB has not expressed any issue with the visual movement of the controls under normal circumstances when one pilot is operating the controls. As incorporated into the wording of the safety issue and safety recommendation, the ATSB's concerns lie with the tactile feedback, particularly in the absence of visual or auditory cues (for example, dark night conditions where crew resource management breaks-down), and there are no artificial systems to alert the flight crew (such as a dual input warning).
The ATSB agrees that the pilot will experience an unusual effort on the controls. However, it does not explicitly indicate to the pilot the origin of that unusual effort. Unlike systems with rigid interconnections, the control column can move consistent with their input (for example, forward movement from pushing the controls), but not necessarily consistent with the resultant output. This was shown mathematically in appendix C of the investigation report. Because a pilot can get control movement consistent with their input, the system does not provide the pilots with tactile feedback that positively signals to them that there are dual control inputs. As discussed in the report, when the visual and auditory communication channels have failed, then the tactile communication channel is all that remains.
The actions taken by ATR with regard to dual control inputs and crew resource management has merit but does not address the reduced tactile feedback. With regard to the list of safety actions that ATR consider having addressed the safety issue, all of those actions were taken well in advance of the release of the final report, so have added no new information. As such, the ATSB does not consider the identified safety issue to have been adequately addressed by ATR.
