Regional operator Skippers Aviation has taken safety action after a Fairchild Metro 23 twin-turboprop airliner descended below the lowest safe altitude while its crew responded to smoke in the cockpit and a wing overheat indication on a passenger flight from Perth last year.
The serious incident occurred on 15 August 2024, during a flight from Perth to Bronzewing Airport, Western Australia, with 12 passengers and 2 flight crew on board.
Climbing after take-off, the crew observed hot air and smoke from the flight deck air vents. The smoke increased, and the crew initiated the 'smoke in aircraft' checklist.
"Required items on the checklist were not completed," Australian Transport Safety Bureau Director Stuart Macleod said.
"Specifically, the first officer did not don an oxygen mask due to difficulty with its usage, and the left bleed air system was not switched off."
The ATSB's final report into the incident notes the hot air and smoke was the result of a failure within the left air cycle machine prior to departure.
The crew commenced preparations for a return to Perth, but with the left bleed air system remaining on, smoke continued to enter the cabin. The left wing overheat light later illuminated, so the crew actioned the 'wheel well and wing overheat' checklist.
While actioning this second checklist, the crew did turn the left bleed air system off, and smoke ingress into the cabin ceased.
"However, the crew did not complete the required action of extending the landing gear," Mr Macleod observed.
"This missed checklist item potentially increased risk, had the wing overheat indication been associated with a brake fire or wheel well overheat issue."
During the return to Perth, the aircraft deviated both above and below the altitude assigned by air traffic control, including a descent to 639 ft below the lowest safe altitude.
"The ATSB determined the high workload associated with responding to the smoke and wing overheat indication adversely affected the flight crew's performance," Mr Macleod said. "This resulted in errors in flight path adherence, checklist completion and decision making."
The aircraft landed back in Perth without further incident.
Following the occurrence, Skippers Aviation conducted a refresher training course for flight crew on emergency response briefings and a theory examination for flight crew on bleed air, pneumatics, pressurisation and fire warning systems.
Practical training sessions were also held for flight crew on revised emergency procedures and the use of the crew oxygen system.
Skippers also changed its Metro 23 flight crew training program to include a revised Line Oriented Flight Training program, including more comprehensive oxygen system training and a presentation on the Metro 23's oxygen system.
"This occurrence highlights the importance of careful and methodical checklist completion, particularly during periods of high workload," Mr Macleod summarised.
"It also emphasises the importance of flight crew being familiar with onboard emergency equipment, and how to use it."
While not contributing to the occurrence, the ATSB also identified the air traffic controller did not identify or correct a readback error by the first officer during the return to Perth.
Additionally, later when the aircraft first descended below the lowest safe altitude, the crew were advised of the deviation by air traffic control, but the required 'safety alert' was not issued.
You can find here the report: Smoke in aircraft and descent below lowest safe altitude involving Fairchild Industries SA227-DC, VH-WBQ, 25 km north-east of Perth Airport, Western Australia, on 15 August 2024
