The insulation blanket of a plane that dropped 17,000 feet in six minutes mid-flight was not installed correctly and clogged an air valve, affecting the cabin pressure, an investigation has found.
The QantasLink Fokker 100 aircraft was carrying passengers from Perth to Geraldton on August 10, 2020, cruising at 26,000 feet when the flight crew received an excessive cabin altitude warning.
Oxygen masks were deployed and the pilot launched an emergency descent before the plane levelled off at 9000 feet and continued to Geraldton.
At the time passengers told local media they were startled.
One passenger sitting in the front row told the Geraldton Guardian the crew was to be commended.
“The crew did a fantastic job … The pilot asked if there were any questions,” he said in August.
“Everybody was quite impressed.”
An engineering inspection has since determined that an insulation blanket had “migrated from its location” and became wedged in one of the pressurisation system’s two air outflow valves, which affected the aircraft’s ability to maintain cabin pressure.
According to the Australian Transport Safety Bureau’s investigation, the insulation blanked had likely “not been properly secured to the aircraft‘s structure” during recent heavy maintenance.
On the aircraft, insulation blankets in the same area as outflow valves were able to dislodge and move if not correctly secured, ATSB acting director transport safety Vik Chaudhri said.
“The investigation found that while the aircraft manufacturer’s instructions detailed that during maintenance installation blankets could be removed ‘as necessary’, those instructions did not reference the insulation blanket installation procedure,” Mr Chaudhri said.
“This resulted in insulation blankets not being properly secured to the structure.”
Qantas subsidiary Network Aviation conducted a fleet-wide inspection of its Fokker 100 fleet in response, identifying a “number” of aircraft with incorrectly installed insulation blankets.
Virgin Australia and Alliance Airlines have since carried out their own inspections for incorrectly installed insulation blankets.