Report: Learjet near-accident due to “inappropriate prioritisation and allocation of pilot´s workload”

The Swedish Accident Investigation Board (SHK) released their final investigation report into a an incident involving a Learjet near Stockholm. The aircraft  deviated from the cleared altitude and descended below the minimum obstacle clearance altitude.

An Austrian Learjet 40 corporate jet was involved in an incident in November 2008 during a positioning flight from Paris-Le Bourget (LBG) to Stockholm-Bromma Airport.

The flight was radar vectored at the incident; the co-pilot was PF and was operating the aeroplane on autopilot according to instructions from the ATC about heading, altitude and speed. The minutes preceding the incident there was one instruction about heading change and four instructions to reduce the speed. When the new heading, left 330 degrees, was confirmed, the PF selected the new heading on the autopilot panel. The flight was at the same time cleared for ILS-approach, and the APPR-mode was selected on the autopilot panel. The aeroplane was apparently not commencing the turn to the new heading, but continued straight ahead. The pilots were at this moment also busy with checklist reading and other preparations for the imminent landing.

When the pilots realised that they were going through the approach track, the PNF disconnected the autopilot and made a steep left turn to join the inbound track. This action was aimed at helping the PF to quickly point the aeroplane into the approach direction. The PNFs take-over of the controls was not made by the use of standard phraseology. During the left turn towards the approach track, the aeroplane started an unintentional descent. There was no formally correct transfer of controls back to the PF.

The ATC gave warnings and instructions to immediately turn to a heading of 270 degrees and commence a climb, which were confirmed by the pilots.

Somewhat later the GPWS-warning was triggered and the PNF regained the control of the aeroplane by the phrase “I have it”, and commenced a go-around and a left turn. The PNF claims that he had visual contact with the ground at this moment, but not with the runway, and that he was aware of obstacles in the area, i.e. the radio/TV-broadcasting antennas. After climbing to 2500 feet, the ATC issued new headings and the approach to runway 30 at Stockholm-Bromma was carried out with no further deviations.

The height of the antennas are about 1370 feet (about 418 m) above sea level and the lowest altitude of the aeroplane was about 650 feet (about 200 m).

The incident was caused by inappropriate prioritisation and allocation of the pilot´s workload.

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