FAA flags 737 flight-management software issue affecting vertical navigation

The Federal Aviation Administration has issued a safety information bulletin describing a flight-management software issue that can affect vertical navigation on Boeing 737 aircraft. The bulletin, dated 3 October, says the problem stems from an error in flight-management computer software versions U14 or U14.1.

Potentially affected aircraft include older-generation 737s from the -600 upward, along with all currently certified 737 Max variants.

According to the bulletin, the issue appears when a crew carries out a missed approach and then navigates directly to a waypoint that is not part of the approach associated with the airport. In that situation, the aircraft can disconnect and transition away from vertical navigation mode, or VNAV, to what the bulletin describes as a simpler level of automation for pitch control.

If pilots want to fly the subsequent approach using vertical navigation after executing the missed approach, the bulletin states they would need to carry out additional procedural steps.

The FAA is not requiring operators to take action. It recommends that operators of affected aircraft follow Boeing guidance published on 2 October.

The bulletin says Boeing took the issue to its safety review board, which determined the event should not be considered to pose an unsafe condition. The FAA said it independently brought the matter to its corrective action review board, which reached the same conclusion.