On 26 December 2008, a DHC8-300 being operated by Eastern Australia Airlines on a scheduled passenger flight from Moree to Sydney made an auto Instrument Landing System (ILS) approach in day Instrument Meteorological Conditions (IMC) to the destination landing runway which became de-stabilised and was continued as such until a stick shaker activation occurred. A go around had then been commenced and the subsequent approach to land was flown uneventfully with the aircraft put into landing configuration earlier and stabilised approach criteria met.
An Investigation into the event was carried out by the ATSB. It was established that the First Officer had been the PF and that both pilots had been aware of their Company requirements for an ILS approach, the Stable Approach Criteria and the prescribed procedures for a go-around. The First Officer was relatively inexperienced and had low hours on type whereas the aircraft commander was experienced with high hours on type.
Flight Data Recorder (FDR) data indicated that the FAF for the ILS approach to Runway 34L had been approached level at 2000 ft and at a speed of 185 knots. At ILS GS capture about 0.5 nm prior to the FAF, the aircraft pitched down and speed increased to 195 knots. In response, the PF had responded by retarding the power levers to Flight Idle and requesting the PNF to advance the propellers to maximum rpm. A rapid decrease in airspeed followed which allowed the extension of the landing gear and the selection of Flap 15°. The PNF advised noticing a little later that the airspeed was about 120 knots and decreasing and called ‘check speed’. The FDR data showed autopilot disconnection at that time and an altitude of 1160 feet. The stick shaker activated and the aircraft commander called for a go-around. However there was a delay in initiating this which resulted in a further stick shaker activation occurring 4 seconds after the initial one. After a short interval of apparent indecision by the PF, the go around was commenced. A second uneventful approach to the same runway was then completed during which landing gear down and Flaps to 15° were selected prior to the FAF.
The investigation considered that the inappropriate timing of aircraft configuration and the apparently unexpected initiation of ILS GS descent led to an unanticipated increase in the flight crew workload which distracted the crew from properly monitoring aircraft performance. Unnoticed, this led to an unstable aircraft state that preceded the activation of the stick shaker. It was concluded that had the crew initiated a go-around and missed approach earlier, the unstable state and stick shaker activation could have been averted.
The following ‘Contributing safety factors’ were identified:
- There was a lack of communication between the flight crew relating to the configuration and position of the aircraft on the approach.
- The crew were aware that the aircraft was not appropriately configured prior to the Final Approach Fix, but did not initiate a missed approach as required by the operator’s Standard Operating Procedures.
- The late change in the aircraft’s configuration increased the flight crew’s workload to the extent that they did not detect the decreasing airspeed.
- The aircraft’s performance deteriorated to a point that the stick shaker activated.
It was also considered that the fact that “the stick shaker recovery procedure was not conducted in accordance with the operator’s standard operating procedures and the decision to action a go-around was delayed” had also been a factor.
As a result of the incident, the Operator advised having made related changes to its DHC-8 training syllabus and re-alerted crews to both the de-stabilising effects of changes to aircraft configuration during an approach and the importance of good communication in a multi-crew environment.
The Final Report of the Investigation was published on 8 June 2010 and may be seen in full at SKYbrary bookshelf:Aviation Occurrence Investigation AO-2009-001
No Safety Recommendations were made.