Cabin altitude warning highlights the importance of checklist management

A cabin altitude warning alarm on a Boeing 737 due to air conditioning pack switches being left in the OFF position highlights the importance of effective checklist management, a new ATSB investigation reports says.

Close-up view of air conditioning pack switches

As the 737 climbed through 13,500 feet during a July 2018 scheduled airline flight from Melbourne to Sydney, the aircraft’s cabin altitude warning horn sounded, resulting in the pilots donning oxygen masks. On hearing the alert the First Officer, who was the Pilot Flying, identified that both air conditioning pack switches were set to OFF, and immediately switched them to AUTO.

The Captain took over control of the aircraft and after the crew completed the remainder of the cabin altitude warning checklist, and with cabin pressure under control and operations normal, the flight continued to Melbourne.

Flight crews are reminded that effective checklist management is essential for verifying that critical procedural items are undertaken and ensuring safe aircraft operation.

The ATSB’s subsequent investigation of the incident found that normal procedures and checklists, which were designed to ensure that the aircraft is correctly configured for flight, were not completed due to a number of factors, including training, distraction, high workload, low expectancy of error, and supervision lapses.

“Flight crews are reminded that effective checklist management is essential for verifying that critical procedural items are undertaken and ensuring safe aircraft operation,” ATSB Director Transport Safety Dr Stuart Godley said.

The investigation noted that the the First Officer, who was under supervision from the Captain ahead of being checked to the line on the 737, had significant experience on other aircraft types. The First Officer had only recently joined the airline and a lengthy break in flying roles and significant gaps in the training program may not have allowed him sufficient time to consolidate the procedures to an intuitive level that was resilient to error.

As the First Officer was very experienced, the Captain may have relaxed his supervision of the First Officer, thus contributing to him not identifying the error at the time.

“Although a highly experienced pilot, the First Officer was still a trainee on the Boeing 737 and as such, required vigilant supervision of a training captain. This is a crucial defence against error by trainee pilots,” Dr Godley said.

Read the investigation report AO-2018-054:  Incorrect configuration involving Boeing 737, VH-VUB, near Sydney, NSW, on 12 July 2018

Last update 30 September 2019