Investigators have identified problems with Air New Zealand crew not following checklists and training in the use of emergency oxygen masks following a potentially dangerous depressurisation incident aboard an Auckland-bound plane.

An unexpected loss of cabin pressure can cause both passengers and crew to lose consciousness rapidly from a lack of oxygen and has been the cause of fatal crashes overseas.

The Transport Accident Investigation Commission was unable to identify the cause of the depressurisation aboard the 737 plane with 81 passengers and crew on board on August 30, 2013.

The plane lost cabin pressure as it descended through 30,000 feet on a flight from Wellington to Auckland and two pilots put on oxygen masks. Masks also deployed for passengers in the cabin.


The plane descended to 10,000 feet - when the cabin altitude warning ceased. Some crew and passengers said the cabin seemed hot and many noticed a chemical smell.

Pilots landed the aircraft safely. The report states some passengers reported ear or sinus discomfort for several days afterwards but otherwise there were no injuries.

The Commission made findings relating to the following safety issues:

• The pilots did not follow exactly the emergency checklist actions which increased the risk of an action being omitted or a required sequence of actions being altered."

• The actions of some of the cabin crew during the incident showed that their emergency training had not sufficiently stressed the importance of sitting down and fitting a mask without delay and had not allowed for a range of scenarios or adequately familiarised the crew with oxygen equipment.

The commission said Air New Zealand acted to correct these issues and therefore it made no recommendations regarding them.

Air New Zealand chief flight operations and safety officer Captain David Morgan said today safety was the airline's highest priority.

``We welcome any opportunity to further improve our training and procedures which we have done in light of the learnings taken from this incident.''

Since the incident the airline had retired its Boeing 737 aircraft with the last 737 exiting the fleet last year.

Issues with a safety checklist from plane maker Boeing were also identified.

"In addition, the inquiry considered the potential for the cabin to be pressurised on the ground following the use of the Cabin Altitude Warning checklist. Boeing subsequently amended the checklist to reduce that risk," the commission said.

Key lessons included the need for where oxygen masks are fitted, passengers and cabin crew must put on their masks and await further instruction from the flight crew.

Others included:

• An aircraft door will be very difficult to open on the ground while the cabin is still pressurised, and this can delay an evacuation if it is called for. When pilots have been controlling the cabin pressure manually, they must ensure that the cabin is fully depressurised to allow the doors to be opened

• Special care must be taken with the maintenance of aircraft emergency equipment, such as oxygen systems.

Read the full incident report here: