The Federal Aviation Administration is investigating a software glitch in versions 14 and 14.1 of the flight management computer on some Boeing 737 MAX aircraft. The issue can cause the vertical navigation system, known as VNAV, to disengage during a go-around following a missed approach when pilots alter a pre-programmed flight plan with the autopilot engaged.

Boeing notified operators of the potential problem in a bulletin issued late last month. The company stated that the glitch does not pose an immediate safety concern and reinforced existing pilot procedures for handling such cases. Engineers at Boeing are developing a permanent software update to resolve the matter.

Southwest Airlines and United Airlines informed Boeing that they will not accept delivery of new 737 MAX aircraft equipped with the affected software versions. Those carriers have opted instead for an earlier software release. Other major U.S. operators, including Alaska Airlines and American Airlines, confirmed that their existing MAX fleets do not use the problematic versions.

The glitch emerged from a recent cockpit software update and affects aircraft involved in the certification of the MAX 7 variant. The FAA certified that model in early August using the newest software. Regulators said they are working closely with Boeing and airlines and will convene a Corrective Action Review Board to assess the matter. The agency pledged to take immediate action if a safety concern is identified.

This development adds to ongoing regulatory scrutiny of Boeing's production and quality processes. The manufacturer has faced repeated challenges in restoring trust following prior safety incidents involving the 737 MAX family.

Boeing said it learned of the issue from an operator in November 2024 but initially determined it did not meet internal criteria for a formal safety review. The company continues to work on a fix targeted for early 2028.