| Occurrence Briefs are concise reports that detail the facts surrounding a transport safety occurrence, as received in the initial notification and any follow-up enquiries. They provide an opportunity to share safety messages in the absence of an investigation. |
What happened
On 19 January 2020, a Boeing 737-800 departed Brisbane, Queensland for a commercial passenger flight to Melbourne, Victoria. There were 6 crew and 178 passengers on board.
Passing FL 250 on climb near Gold Coast Airport, Queensland, a cabin crew member advised the flight crew that a passenger alerted them to a panel hanging off the rear of the aircraft’s left wing. The flight crew requested that the cabin crew further investigate, and discontinued the climb and levelled off at FL 300.
The cabin crew subsequently showed pictures to the flight crew of the dislodged panel on the trailing edge flap area of the left wing. The crew then contacted air traffic control and requested a clearance to descend and return to Brisbane. The aircraft landed without incident and taxied to the gate.
Engineering inspection
Following the incident, the engineering inspection revealed that the inboard trailing edge flap on the left wing had delaminated (Figure 1). The engineers determined that the delamination was due to moisture ingress and excess heat from the engine exhaust.
Figure 1: Delaminated section on the aircraft’s left wing
Source: Operator’s engineering department
Figure 2: Diagram of trailing edge assembly
Source: Operator’s engineering department
Safety action
As a result of this incident, the manufacturer and operator have advised the ATSB that they are taking the following ongoing safety actions:
Manufacturer
- Boeing will be supplying a modified metallic assembly to be installed on aircraft.
Operator
- The operator conducted a fleet inspection of its aircraft aged 10 years old or older and found 7 other aircraft had delamination findings recorded. Due to delamination findings, the inspection program was expanded to flaps on aircraft 6 years old or older, to identify potential early defects on younger aircraft.
- A full damage analysis of the completed inspections and expanded program will support the determination of an effective threshold interval for introducing scheduled inspections via a new aircraft maintenance program task.
- Introduction of a modification program to replace the composite bonded assembly wedge with a new design metallic semi-monolithic assembly (Figure 3).
Figure 3: Diagram of new metallic semi-monolithic assembly for trailing edge flap
Source: Operator’s engineering department
Safety message
This incident provides a reminder that although flight crews conduct extensive pre-flight inspections, unexpected failures may still occur in flight. In this situation, the flight crew took all possible precautions by following the relevant procedures, conducting additional checks to assess the situation, providing clear communications to ATC and returning the aircraft to land.
About this report
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.