The Australian Transport Safety Bureau (ATSB) issued a formal safety recommendation to Indonesia AirAsia, asking that it review its pre-flight safety briefing and safety information card.

The Australian Transport Safety Bureau (ATSB) issued a formal safety recommendation to Indonesia AirAsia, asking that it review its pre-flight safety briefing and safety information card.

This follows a pressurisation incident that took place on 15 October 2017, involving one of the carrier’s Airbus A320s, which returned to Perth after take-off. The aircraft, registered PK-AXD, was carrying 146 passengers and six crew members on board, and was bound for Denpasar.

Just before midday local time, and as it was climbing through 25,000ft, the pilots noticed repeated fault messages from the aircraft pressurisation system. However, when the crew accessed the flight management system’s pressure page, the fault cleared.

As the A320 continued its climb, the master caution activated for opening of the cabin pressure system safety valve. The flight crew, which reported feeling discomfort, took over control of the pressurisation system manually, and attempted to reduce the cabin pressure climb rate.

The warning signal for high cabin altitude then flashed intermittently for about 10 minutes, during which the flight crew decided to request to make an emergency descent to 22,000 feet, citing pressurisation issues. They later amended it to 10,000 feet.

As the aircraft made its descent, the cabin crew noticed that the cabin oxygen masks had not been deployed, and reported this to the flight crew, which then manually did so.

The aircraft later reached its intended cruising altitude and proceeded to land at Perth. No injuries or damage to aircraft were recorded.

Investigators later traced the incident cause to a malfunction in the cabin pressurisation system, which led to “incorrect control” of the outflow valve. Consequently, this caused the cabin to be over-pressurised, they note.

The ATSB found that Indonesia AirAsia had “reviewed and elected not to incorporate the manufacturers’ recommended, but not mandatory, improvements to the pressurisation system”.

“The improvements were communicated to the airline by service bulletins. Incorporating the bulletins would have likely prevented the emergency descent incident,” they add.

However, investigators flagged a more pertinent issue in relation to the cabin crew’s handling of the situation.

When oxygen masks were deployed, they note that “several units either did not deploy, or deployed but did not provide oxygen”.

“Consequently, several passengers moved around the cabin to secure a spare oxygen mask,” the ATSB says.

This, coupled with the cabin crew’s shouting of commands like ‘Brace’, ‘Get Down’ and ‘Crash position’, “probably increased the level of confusion and panic amongst some passengers” as the aircraft made its emergency descent.

More than half of the passengers from the flight surveyed by the ATSB said they did not know if oxygen were flowing from their masks, and several others said they were unsure how the equipment operates.

To this end, the ATSB stresses that the cabin crew take on a safety leadership role during emergency situations, and that improved training could help reduce similar occurrences in the cabin.

“Role-playing abnormal passenger behaviour in emergency drills could offer the operator’s cabin crew assessors with the opportunity to expose their trainees to more complex scenarios, and provide a more realistic assessment of the trainee’s ability to take command of an emergency situation,” ATSB investigators note.

Cirium fleets data indicates that PK-AXD was first delivered to AirAsia in 2007, before being handed over to Indonesia AirAsia two years later. It is still flying with the low-cost carrier.