What happened
On 5 April 2019, a Dassault Aviation Falcon 900B, registration ZS-DFJ, was operating an unscheduled charter flight from Robert Gabriel Mugabe International Airport to Victoria Falls International Airport. The aircraft was carrying two crew members and eight passengers.
While descending through FL250, the pilot-in-command noticed that several critical flight displays, including the EHSI, EADI, and MFD, began flashing before going dark. Simultaneously, various master caution warnings were triggered. Shortly after, smoke was observed entering the flight deck from the overhead ceiling panel. The crew immediately donned oxygen masks and initiated emergency checklists for electrical smoke and fire. After declaring a Mayday, the aircraft was granted priority landing at Victoria Falls. The smoke began to dissipate as the aircraft descended through FL190, and the crew landed the aircraft safely at 0602Z. No injuries were reported.
The investigation
SACAA AIID investigators examined the aircraft's electrical systems and recent maintenance history. The investigation focused on a wiring loom located in the flight deck ceiling that had sustained burn damage. The inquiry also reviewed a modification performed on 30 August 2018, which involved the installation of an ADS-B system. This modification required routing an additional wire through an existing part of the wiring loom.
Findings
- The aircraft sustained damage to a wiring loom and heat damage to a ceiling panel.
- The primary cause of the incident was damage to the wire insulation caused by improper handling during a modification.
- During the installation of the ADS-B system, a new wire was threaded through a mounting clamp. It is believed the clamp was not opened during this process, leading to the insulation being compromised.
- The exposed wire subsequently began to arc against the clamp, generating high temperatures that resulted in the electrical fire and subsequent smoke in the flight deck.