On 7 March 2014, at about 1100 Western Standard Time, a Fairchild SA227DC, registered VH-ANW, with a crew of two and 18 passengers departed Truscott-Mungalalu aerodrome and was on climb passing through FL 125 when the cabin altitude annunciator illuminated.
The pressurisation system was checked by the crew and the cabin altitude was observed to be climbing at around a 1,000 feet per minute. While the flight crew were fitting (donning) their oxygen masks the CARGO DOOR warning light also illuminated. They then completed the checklist items which included turning off the engine air bleeds.
As part of the depressurisation drill the first officer made a passenger announcement (PA) requiring all passengers to don oxygen masks. This PA could not be heard by any of the passengers in the cabin. After approximately 5 minutes, a passenger seated in the front of the cabin noted that the crew had donned their masks so went forward to ask if the passengers needed to do the same. This message was then passed throughout the cabin.
As the aircraft was above the maximum landing weight for a return to Truscott, the crew made the decision to continue on to Darwin and, due to the lower cruise altitude required when unpressurised, deviations from the track were necessary in order to avoid any significant weather.
The crew reported that after an uneventful landing in Darwin and engine shutdown, they debriefed the passengers.
They also reported that there were no issues experienced when closing the door at Truscott and that prior to engine start an additional confirmation check was made that the cargo door warning lights were extinguished. It was noted however, that there had been issues with that door in the previous weeks, including being hard to lock and a loss of cabin pressure.
Maintenance examination of the aircraft found that several of the ten locking pins on the cargo door were worn. As a precaution, seven of these pins were replaced. The pilot’s oxygen mask microphone was tested as serviceable and the first officer’s microphone was found to be faulty and was also replaced.
The operator has introduced amendments to the aircraft type PA and safety procedures checklists in order to confirm safety related PA announcements to passengers in these low capacity aircraft are understood and complied with.
The incident highlights the need, in lower capacity passenger aircraft without flight attendants, to assist in the cabin to confirm compliance with safety related announcements for the flight crew to confirm that the passengers have understood and complied with any safety message.