Synopsis
On 18 March 2022, a Vulcanair P.68 Observer 2 aircraft, registration EI-ODA, was parked on the apron at Weston Airport, County Dublin, Ireland, preparing for an aerial survey flight. During engine start-up and subsequent electrical system checks, the mission equipment power supply cable produced electrical arcing and smoke. The pilot shut down the engines and turned off all electrical power. Both the pilot and the task specialist evacuated the aircraft without injury. The aircraft sustained no structural damage, but the mission equipment power supply cable was significantly damaged.
History of the Occurrence
At approximately 12:00 UTC, the pilot, seated in the left cockpit seat, started both engines while the aircraft was stationary on the apron. The aircraft was equipped with mission equipment including a gyroscopically stabilised mount, an aerial survey camera, and a control system. A task specialist was in the cabin to operate the equipment. After engine start, the pilot activated the mission equipment electrical power via a 'Mission Master' switch when requested by the task specialist. Shortly after, the task specialist asked the pilot to deactivate the switch to perform further checks. When the checks were complete, the pilot reactivated the switch. An aural alert sounded, and the pilot noticed a reduction in voltage. Simultaneously, the task specialist signalled a problem. The pilot observed smoke emanating from the mission equipment power supply cable. He immediately shut down both engines and turned off all electrical power, which stopped the smoke. Both occupants exited the aircraft normally. The pilot briefly re-entered to pull the mission power circuit breaker. They monitored the aircraft from outside for approximately 35 minutes. The airport fire and rescue service was not called.
Injuries
No injuries were reported to the investigation.
Damage
The aircraft was undamaged. The mission equipment power supply cable, a two-core insulated cable running along the cabin floor, sustained substantial damage at multiple locations due to electrical arcing and heating.
Personnel Information
The pilot held a Commercial Pilot Licence issued by the Irish Aviation Authority, with a Multi-Engine Instrument Rating valid until 31 January 2023 and a Class 1 Medical Certificate. He had a total of 3,000 flying hours, including 6 hours and 25 minutes on type. He had been briefed on the 'Mission Master' switch operation. The task specialist, responsible for operating the mission equipment, had received training from the operator, including Crew Resource Management and firefighting. He reported that when the mission power was first switched on, the camera appeared unpowered. After several power cycles, he noticed a burning smell, felt the cable was hot, and heard a gushing noise. He turned and saw sparks and smoke from the cable connection at the rear cabin power outlet. He deactivated the mission equipment, and the pilot shut down the engines before they both evacuated.
Aircraft Information
The Vulcanair P.68 Observer 2 is a high-wing, all-metal twin-engine aircraft with a maximum take-off weight of 2,084 kg. It is powered by two Lycoming IO-360-A1B6 engines driving three-blade propellers. The electrical system is 28 V DC. The aircraft had a valid Certificate of Airworthiness and Airworthiness Review Certificate issued on 15 December 2021, with the last 100-hour/annual inspection performed on that date. A Supplemental Type Certificate had been issued for the installation of the mission equipment.
Probable Cause
The investigation determined that the probable cause of the occurrence was mechanical damage to the mission equipment power supply cable as a result of being caught in part of the mission equipment, leading to electrical short circuiting, heating, and arcing.