What happened
On 22 February 2012, an ATR42-300, registration EI-FXA, was performing a commercial passenger flight toward Glasgow Airport. During a radar-vectored ILS approach, the aircraft's speed decreased significantly, triggering the stall alert and stick shaker. The commander immediately responded by pitching the aircraft nose-down and applying full power to recover.
This corrective action caused the aircraft's airspeed to increase rapidly, exceeding the flap 15° Vfe limit and activating the overspeed warning. The airspeed peaked at 174 KIAS. Following the recovery, the aircraft continued the approach, but upon touchdown, a nacelle overheat warning activated. The crew did not follow the prescribed procedures for the overheat warning and subsequently taxied the aircraft to its parking position.
The investigation
The AAIB investigation examined the flight crew's recent duty history, the aircraft's technical systems, and the flight data. Analysis of the crew's schedule revealed that the commander had completed a long drive to his base and was operating his first night flight following a period of daytime sleeping. This suggested that fatigue may have been a factor in the crew's performance.
Investigators also reviewed the Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR). During the FDR readout, it was discovered that certain parameters, specifically the aileron and elevator positions, were being displayed incorrectly due to an error in the data conversion process. This error had persisted through previous readouts without being detected by the operator.
Findings
- The crew failed to maintain the appropriate airspeed during the approach because standard operating procedures were not observed.
- The commander's monitoring and adherence to company procedures were compromised, including the use of non-operational conversation below FL100 and the omission of required briefing topics.
- The performance of the crew was likely affected by tiredness or fatigue, resulting from a diminished quality of rest in the period preceding the flight duty.
- The crew's cooperation during the recovery phase was diminished, as the commander's responses to the co-pilot's monitoring calls discouraged effective cross-cockpit communication.
- The aircraft's FDR contained incorrect conversion data for certain parameters due to a long-standing issue with the data frame layout documentation.