FAA not mandating operator action but advises following Boeing guidance on addressing flight-management computer issue.
US regulators have detailed the flight-management software issue affecting vertical navigation on Boeing 737 models, recommending that operators of affected aircraft follow the airframer’s guidance.
Older-generation 737s from the -600 upwards, as well as all currently certified 737 Max variants are potentially affected.
The issue centres on an error in flight-management computer software versions U14 or U14.1, according to a 3 October safety information bulletin from the US FAA.
It manifests itself if the crew conducts a missed approach and navigates directly to a waypoint which is not part of the approach associated with the airport.
This can result in a disconnection and transition away from vertical navigation mode, or VNAV, to a “simpler level of automation” for pitch control, says the bulletin.
If the pilots, having executed the missed approach, want to conduct the subsequent approach with vertical navigation, they would need to perform “additional procedural steps”, it adds.
While the FAA has advised of the issue, and is recommending following Boeing guidance published on 2 October, it is not mandating actions.
“Boeing took this issue to their safety review board and made the determination that this event should not be considered to pose an unsafe condition,” adds the bulletin.
“Independently, the FAA took this issue to our corrective action review board and made the determination that this event does not represent an unsafe condition.”
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