What happened
On 21 December 1997, a Cessna 152, registration G-BNGD, was being flown from Carlisle to Prestwick. The pilot, intending to ensure the aircraft was available for use during the Christmas period, had flown to North Wales earlier that day to inspect a potential aircraft purchase before returning to Carlisle to collect G-BNGD.
During the flight, the pilot encountered deteriorating weather. To avoid cloud, the pilot opted for a low-level coastal route. However, as darkness fell and the aircraft entered cloud cover, the pilot reported a failure of the suction pump, which powered the aircraft's Attitude Indicator and Direction Indicator. Because the electrically powered Turn Co-ordinator had been unserviceable for several months, the pilot was left without any gyroscopic attitude references while flying in Instrument Meteorological Conditions (IMC).
Radar data showed the aircraft performing several left-hand orbits. The final transmission from the pilot, which was partially unintelligible, included the word 'descending'. The aircraft subsequently struck high ground near Cairnharrow at a high rate of descent, resulting in one fatality and the destruction of the aircraft.
The investigation
Investigators examined the wreckage and the aircraft's maintenance history. The investigation focused on the vacuum system, which provided suction to the gyroscopic instruments. While the vacuum pump itself had not failed, evidence suggested that a hose between the regulating valve and the pump may have become disconnected. This disconnection could have been caused by the recent repair of the rudder bar assembly in the same cockpit area, or it may have occurred during flight due to inertial forces.
Findings
- The pilot was flying in darkness and cloud without any functional gyroscopic attitude or heading references.
- The loss of vacuum suction rendered the primary flight instruments unserviceable.
- The pilot became disorientated due to the lack of visual references and the absence of working instruments.
- The aircraft entered a spiral dive from which recovery was unlikely given the circumstances.