What happened
On 18 March 2022, a Vulcanair P.68 Observer 2, registration EI-ODA, was parked at Weston Airport in preparation for an aerial survey mission. While the aircraft was stationary on the apron, the pilot started both engines and, at the request of a task specialist in the cabin, activated the electrical power for the onboard mission equipment.
Shortly after the power was engaged, the pilot noticed a drop in aircraft voltage and an aural alert. Simultaneously, the task specialist reported a burning smell and observed smoke and sparks emanating from an electrical cable. The pilot immediately shut down the engines and deactivated all electrical power, which halted the smoke production. Both the pilot and the task specialist evacuated the aircraft safely, and the pilot later pulled the mission power circuit breaker to ensure the system was isolated. No injuries occurred during the event.
The investigation
The AAIU investigation focused on the electrical system modifications and the physical state of the mission equipment cabling. Investigators examined the Supplemental Type Certificate (STC) used to install the mission equipment and the installation instructions provided by the design organization.
During the inquiry, it was discovered that the installation instructions had originally specified an incorrect male-type power outlet, though this was corrected in a later revision. The investigation also looked into the fire protection capabilities on board, noting that while the aircraft met existing regulatory requirements, the single fire extinguisher was located in the cockpit and would have been difficult for a cabin occupant to access during an in-flight emergency.
Findings
- The primary cause of the incident was mechanical damage to the mission equipment power supply cable, which occurred because the cable was caught between the stabilizer mount and its housing during operation.
- This mechanical damage led to electrical short-circuiting, heating, and arcing.
- The mission equipment power supply cable was not properly secured or clamped to the aircraft cabin, allowing it to lie loose and coil over itself.
- The electrical system lacked effective overload protection for the specific mission supply cable.
- The installation of the mission equipment itself had not been submitted as a 'Minor Change' to the appropriate aviation authority.
Safety action
As a result of the investigation, a safety recommendation was issued to EASA. The recommendation suggests that EASA review its Supplemental Type Certificate approval process to ensure that firefighting capabilities are adequately considered whenever new electrical equipment is installed via an STC.