What happened
On 9 April 2007, a Piper PA-28R-201T, registration G-JMTT, departed Oban Airport for a flight in the hills of Argyll and Butte, Scotland. The flight was intended to be a visual flight rules (VFR) excursion, but the aircraft encountered significant cloud cover and low visibility. During the flight, the aircraft's radar track showed a climbing path that eventually transitioned into a tight left turn and a rapid descent. The aircraft struck a hillside approximately 9 nm south of Oban Airport, resulting in 3 fatalities.
The investigation
The investigation examined the wreckage, the aircraft's maintenance history, and the flight instruments. Investigators found that the aircraft's engine and flight controls were intact prior to the impact, with all failures attributable to the high-speed crash. Examination of the flight instruments revealed that the Attitude Indicator (AI) had become unreliable. Specifically, the investigation focused on the engine-driven vacuum pump, which supplied suction to the AI.
Analysis of the vacuum pump showed that the flex centre coupling had fractured due to torsional overload. This failure likely caused the AI to provide erroneous pitch and roll information. Furthermore, the investigation noted that the commander was not instrument rated and had been declared medically unfit due to a heart condition, though no evidence of medical incapacitation was found. The investigation also identified that the aircraft was operating above its maximum takeoff weight and that the pilots had consumed alcohol the previous evening.
Findings
- The aircraft entered instrument meteorological conditions (IMC) while the crew was not instrument rated.
- The failure of the vacuum pump coupling led to unreliable attitude indications from the AI.
- The aircraft's flight characteristics, including high airspeed and a rapid descent rate, were consistent with spatial disorientation.
- The vacuum pump had exceeded its recommended service life of 500 hours or 6 years.
- The aircraft was loaded to approximately 181 lb above its maximum takeoff weight.