US regulators said a software glitch in Boeing’s best-selling 737 Max aircraft will delay certification of a hotly anticipated new model, in a potential blow to the aerospace giant’s recovery efforts and airlines squeezed by rising fuel costs. Bryan Bedford, head of the Federal Aviation Administration, said on Monday that the agency would not approve the Max 10 until it is “satisfied that we don’t have an issue” with the automated navigation function on some 737s. Shares in Boeing fell 6 per cent on Monday to $184.

As the war in Iran pushes up fuel prices, airlines are desperate to get their hands on the Max 10 — Boeing’s short-haul jet that rivals Airbus’s best-selling A321 — as they look to increase capacity and lower operating costs. A Boeing spokesperson said that “we continue to follow the lead of the FAA as we work through the certification process”. The Max 10, the largest variant of the flagship single-aisle model, is crucial to Boeing’s ability to repair its balance sheet following the fallout from fatal Max crashes in 2018 and 2019 and a door blowout in 2024.

The software glitch, first reported by the Wall Street Journal, can occur when pilots need to change their planned flight path after an aborted landing. The glitch is contained in a software update made in November 2024. Since then, Boeing has delivered 801 737 Max jets, although not all of them included the affected software. Sheila Kahyaoglu, an analyst at Jefferies, noted the FAA was convening a “Corrective Action Board” that could take days or weeks to assess the issue.

Boeing said on the weekend that it had informed all 737 operators of software where “pilots may not have access to automated flight guidance during a specific landing scenario”. The company added that “all pilots are trained to safely land an airplane without automated vertical navigation”. In a statement, the FAA said that “safety dictates the certification timeline. We’re following our safety review process to investigate this software glitch and won’t hesitate to take action if needed.”