What happened
On 13 April 2006, a BAe 146-200, registration G-JEAY, was performing a passenger flight departing from Southampton. Shortly after the aircraft left the airfield, the flight crew noticed the 'attitude' warning flag appearing on the Captain’s Attitude/Direction Indicator (ADI). At the same moment, the Traffic Collision Avoidance System (TCAS) ceased to function.
While the crew attempted to rectify the ADI by switching both indicators to the No 2 system, the TCAS remained inoperative. During this period, cabin crew reported an unusual electrical burning smell originating from the forward galley area. Due to these simultaneous instrument failures and the presence of the smell, the pilot declared a PAN-PAN and initiated a return to Southampton. The aircraft landed without further incident, and passengers disembarked normally.
The investigation
Following the event, the operator's maintenance organisation conducted an inspection of the aircraft. The investigation focused on identifying the source of the electrical smell and the simultaneous failure of the flight instruments.
Technicians located a defective vertical gyro unit within the avionics bay. The inspection revealed that a fault within the power supply of this unit had caused the transformer and related components to overheat, which was the source of the burning odor. The unit was subsequently sent to the manufacturer for further analysis.