The Australian Transport Safety Bureau has issued two safety recommendations following an incident where a horizontal stabiliser bung was not removed from a Saab 340 regional airliner prior to taxi at Cairns Airport.
On 16 November 2022, the Regional Express operated Saab 340B was taxiing for take-off from Cairns for a scheduled passenger flight to Bamaga, Queensland, when an engineer on a nearby parking bay noticed something hanging from the aircraft, and contacted the tower.
The air traffic controller visually confirmed the engineer's observation and alerted the crew, who returned the aircraft to the bay.
"To prevent bird nesting, the operator required its aircraft parked overnight in Cairns to be fitted with a bung installed in each of the two horizontal stabiliser trim actuator coves," ATSB Chief Commissioner Angus Mitchell said.
At interview, no members of the ground crew and flight crew involved in the pre-flight checks recalled seeing either of the bungs installed, nor the tether which connects the two, which has a 'remove before flight' conspicuity flag in the middle.
An inspection conducted once the aircraft returned to the bay identified the bung was still installed in the left trim actuator cove, with the rest of the bung assembly hanging from it.
"The horizontal stabiliser bungs were most likely incorrectly installed - or possibly the tether rope with the 'remove before flight' flag was not hanging from the horizontal stabiliser as designed - resulting in them not being detected during pre-flight preparations and the aircraft being dispatched with the bung installed," Mr Mitchell said.
"Targeted inspection of locations and components, rather than relying on flags which may not always be visible, can help identify when these covers or devices have not been removed."
The ATSB's investigation found the operator had no formal procedures for the storage and accountability of the bungs after they were removed from the aircraft.
It also found the design of the bungs did not consider aspects that would ensure the identification of an installed bung, or the safe operation of the aircraft if the bungs were not removed prior to flight.
The investigation notes the operator has commenced a risk assessment to formalise the procedures around the use of the horizontal stabiliser bungs, and to support this, an engineering order was developed to document and approve the manufacture of the bungs.
"However, these actions do not address the issues around the storage and accountability of the bungs when they are removed or the aspects around the identification of an installed bung or the safe operation of the aircraft if the bungs were not removed," Mr Mitchell noted.
As such, the ATSB has issued Regional Express two safety recommendations and will continue to monitor the progress the operator takes in addressing these.
"When a missed item has the potential to affect the safety of a flight, a secondary means of assuring the item has been removed should be employed," Mr Mitchell concluded.
"Similar to procedures employed for other covers on aircraft, a means to account for what equipment has been removed from the aircraft before being stowed or retained by ground agents will provide the crew with another opportunity to detect when a bung or cover has not been removed."
You can find here the final report: Aircraft preparation event involving Saab 340B, VH-ZLJ, Cairns, Queensland on 16 November 2022
