What happened
On July 13, 2009, a private Gulfstream IV SP, registration VT-MST, departed Kerry Airport for Luton, England. Shortly after takeoff, the aircraft's left-hand windshield fractured due to electrical arcing. The crew requested an immediate return to Kerry Airport.
During the return maneuver, the aircraft's navigation systems intercepted a "false localiser" signal, leading the crew to believe they had captured the correct approach path. Consequently, the aircraft began a steep descent in cloudy conditions. The flight path drifted approximately 6 nautical miles south of the actual instrument landing system (ILS) track, placing the aircraft on a trajectory toward high terrain. The descent continued until the aircraft reached a minimum radio height of 702 ft.
The investigation
The AAIU investigation focused on the sequence of events leading to the altitude loss and the subsequent damage to the aircraft. Investigators examined flight data recorder (DFDR) information, which revealed that the crew had de-selected the autopilot and commenced a descent without a valid ILSD signal. The investigation also looked into the aircraft's technical state, discovering that the No. 1 engine had suffered significant foreign object damage (FOD) from a piece of mild steel.
Furthermore, the investigation reviewed the crew's performance and the air traffic control interactions. It was noted that the crew provided inaccurate position reports to Kerry Tower, which hindered the controller's ability to maintain situational awareness. The investigation also found that the crew performed several high-power engine ground runs after landing, which likely worsened the existing engine damage.