Undetected cracking resulted in failure
Date issue released
Safety Issue Description

Failure of the inboard programming roller cartridge was due to undetected fatigue cracking that occurred in an area that was not included in the detailed flap actuation system inspection.

Issue number
Issue Status
Open – Safety action pending
Transport Function
Aviation: Air transport
Issue Owner
The Boeing Company
Mode of Transport
Issue Status Justification

Since 2017, there have been multiple occurrences involving fatigue cracks and failures at aft flap programming rollers. Boeing is currently reviewing inspections for the programming rollers and examining possible reasons why the failures started occurring after 2017. However, at this stage there has been no reported action that might address the risks posed by future programming roller/cartridge failures.

Response by The Boeing Company

On 15 November 2022, The Boeing Company provided the following response:

Boeing does not concur that this event represents a safety issue, when analyzed within our FAA‑approved risk management program. A review of prior failures shows that airplane-level effects were correctly mitigated by flight crews and the affected aircraft landed without further incident. Boeing’s review indicates that the event does not represent a significant reduction in airplane safety margins, and that the current inspection program is adequate.

ATSB comment in response

The ATSB acknowledges that, based on consideration of the consequence of the component failure, Boeing’s risk management program does not classify this as a safety issue. However, the ATSB also believes that the reduction in safety margins involving a passenger‑carrying aeroplane and the frequency of occurrence—particularly in the past 5 years— warrants safety improvement in the detection of fatigue cracking prior to failure.

The ATSB also notes that a detailed inspection of the flap actuation system already exists, and while it includes the aft flap rollers, it does not include the cartridges that house them. Inclusion of the cartridges in the detailed inspection would provide the greatest opportunity for fatigue cracks to be identified prior to failure.

Action number
The Boeing Company
Action Status
Action description

The Australian Transport Safety Bureau recommends that The Boeing Company takes safety action to increase the detection of fatigue cracks in the roller cartridges of 737‑800 aircraft prior to failure.