By Priya Raman

The Federal Aviation Administration has halted certification of the Boeing 737 Max 10 over a vertical navigation (VNAV) software defect that also affects the 737 Max 7 and an undisclosed number of in-service 737 Max jets.

FAA administrator Bryan Bedford told reporters on 28 September that the agency would not clear the long-delayed Max 10 until engineers determined whether the fault presents a safety-of-flight issue. "We haven't concluded whether this is a safety-of-flight issue or not, but we will be delaying the [Max] 10 until we are satisfied that we don't have an issue," Bedford said.

The software, developed by GE Aerospace, governs vertical navigation during go-arounds — the missed-approach procedures pilots initiate when a landing cannot be completed. According to Bedford, an update intended to correct a prior VNAV bug "unexpectedly introduced a new bug," causing the system to drop out of vertical navigation mode and revert to a simpler pitch-control mode.

What does the defect actually do?

Boeing notified operators last month that the affected software may withhold automated flight guidance following a missed approach. "Following a missed approach, when a pilot alters their preprogrammed flight path, the flight management computer software issue may result in the transition from a vertical navigation mode to a simpler level of automation for pitch control," the manufacturer said. Pilots are trained to complete landings without VNAV, Boeing added.

The Wall Street Journal reported on 26 September that Boeing has known of the glitch since 2024. American Airlines, United Airlines and Southwest Airlines told the Journal and FlightGlobal that none of their 737 Max jets carry the affected software load.

What is the FAA doing now?

The agency has convened a Corrective Action Review Board, disclosed through Boeing's internal news network, to determine what response the issue warrants. Bedford framed the review as primarily a workload question — meaning how flight crews respond when VNAV drops out.

"Safety dictates the certification timeline," the FAA said. "We're following our safety review process to investigate this software glitch and won't hesitate to take action if needed."

How does this compare with prior Max issues?

The Allied Pilots Association (APA), which represents American Airlines pilots, backed the regulator's decision. Spokesman Dennis Tajer compared the VNAV defect with earlier Max concerns involving the Maneuvering Characteristics Augmentation System (MCAS) — implicated in two fatal 737 Max crashes — and an engine-related load-reduction device issue that can vent smoke into the cockpit.

"It's not an emergency, but it's not ideal," Tajer said of a VNAV dropout during go-around, when the aircraft operates at low altitude and crews manage multiple tasks.

APA also faulted Boeing for not disclosing the defect sooner so flight crews could rehearse responses. "It's the coach of the team, and it says, 'Here's where we are going,'" Tajer said, referring to VNAV's role in cueing flap retraction during climb-out.

Boeing said it has worked with operators to reinforce existing pilot procedures and is developing a permanent software patch, along with a method for crews to re-enable VNAV.

What does this change for Boeing's delivery plans?

Boeing had aimed to clear the Max 10 with the FAA this year and planned to begin deliveries of both the Max 7 and Max 10 next year. Bedford declined to commit to a new certification timeline.

The Max 7 received FAA certification less than two months before the VNAV disclosure and has not yet entered service.

GE Aerospace confirmed it is working with Boeing and the FAA on a fix. "Safety is our top priority," the engine and avionics group said. "We are working closely with Boeing and will support the FAA's evaluation."

Whether a software patch can restore the Max 10 certification track this year, or whether Boeing's narrowbody backlog absorbs another delay, will hinge on the Corrective Action Review Board's determination and the pace of GE's update.