FAA issues service bulletin on possible VNAV disconnect in 737 NG and MAX
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- The FAA published a Service Bulletin on 3 October 2026 addressing a possible vertical navigation (VNAV) mode disconnection in Boeing 737 NG and MAX aircraft equipped with FMC software versions U14.0 or U14.1.
- WestJet first reported the issue in November 2024; Boeing evaluated it in February 2025, reopened the case after additional reports, notified the fleet in August 2026 and escalated the matter to the FAA. Boeing and GE Aerospace are developing a permanent software patch while Boeing is formalising airline procedures to reactivate VNAV if the scenario occurs. The FAA’s CARB concluded the fault does not constitute an unsafe condition and the bulletin’s recommendations are informational, not mandatory.
- FAA Administrator Bryan Bedford noted that while U14.1 corrected a known vertical navigation fault, it unexpectedly introduced the new issue on 28 September 2026.
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