As a legacy of there being no inspection specific to an in-flight pitch disconnect, there is potential for other ATR aircraft to have sustained an in-flight pitch disconnect in the past and be operating with undetected horizontal stabiliser damage.
The aircraft manufacturer, ATR, did not provide a maintenance inspection to specifically assess the effect of an in-flight pitch disconnect on the structural integrity of the horizontal stabilisers. As a result, if an in-flight pitch disconnect occurred, the aircraft may not be inspected at a level commensurate with the criticality of the event.
Although the design standard for the aircraft (JAR-25) required the control system to be of sufficient strength to withstand dual control inputs, it did not require consideration of the effect that dual control inputs may have on control of the aircraft. Similarly, the current design standard (CS-25) does not address this issue.
Response from EASA
In September 2018, EASA advised the ATSB that:
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.
Flexibility in the ATR 72’s pitch control system between the control columns results in a change in the aircraft’s longitudinal handling qualities and control dynamics when dual control inputs are made. This could result in an aircraft-pilot coupling event where flight crew may find it difficult to control the aircraft.
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.
The En Route Supplement Australia (ERSA) did not have formal guidance for flight crews regarding the limited visual cues for maintaining alignment to runway 11/29 at Darwin during night landings in reduced visibility.
Virgin Australia did not have formal guidance for flight crews regarding the limited visual cues for maintaining alignment to runway 11/29 at Darwin during night landings in reduced visibility.
The absence of centreline lighting and the 60 m width of runway 11/29 at Darwin result in very limited visual cues for maintaining runway alignment during night landings in reduced visibility.
Category I runways that are wider than 50 m and without centreline lighting are over-represented in veer-off occurrences involving transport category aircraft landing in low visibility conditions. The installation of centreline lighting on wider category I runways is recommended but not mandated by the International Civil Aviation Organization Annex 14.
A NAV ADR DISAGREE alert can be triggered by either an airspeed discrepancy, or angle of attack discrepancy. The alert does not indicate which, and the associated procedure may lead flight crews to incorrectly diagnosing the source of the alert when the airspeed is erroneous for a short period and no airspeed discrepancy is present when the procedure is carried out.
Although the NAV ADR DISAGREE had more immediate safety implications relating to unreliable airspeed, the ECAM alert priority logic placed this alert below the engine-related faults. As a result, the NAV ADR DISAGREE alert was not immediately visible to the flight crew due to the limited space available on the ECAM display.
The operator provided flight crew with limited training and guidance relating to the need for crew to re-evaluate their holding speed for a change in altitude (specifically above flight level 200).
The operator provided flight crew with limited training and guidance in stall prevention and recovery techniques at high altitudes or with engine power above idle.
Although CHC Helicopter Australia’s operations manual stated that emergency medical service flights should be conducted under instrument flight rules (IFR) ‘where practical’, its procedures for night visual flight rules (NVFR) operations using night vision goggles did not clearly state when IFR rather than NVFR should be used.
Although the operator had procedures for conducting a verbal safety briefing prior to flight and had safety briefing cards available, its risk controls did not provide assurance that all passengers would understand the required procedures for emergency landings. More specifically:
The Bureau of Meteorology did not have a procedure to ensure that a recording of the local weather forecast for balloon operations in the Melbourne area was correctly uploaded and accessible to balloon pilots.
The engine manufacturer did not have specific inspection procedures in the maintenance documents of the propeller shaft to detect a fatigue crack originating from the dowel pin hole.
Civil Aviation Order 20.7.1B stipulated that a 1.15 (15 per cent) safety margin was to be applied to the actual landing distance for jet-engine aircraft with a maximum take-off weight greater than 5,700 kg. This safety margin may be inadequate under certain runway conditions, which increases the risk of a runway excursion. The corresponding guidance in Civil Aviation Advisory Publication 235-5(0) had not been updated to account for this.
Virgin Australia Airlines/Virgin Australia International did not have a policy requiring crews to independently cross-check environmental information and landing performance calculations in-flight, removing an opportunity to detect crew errors.
