Boeing has found a new glitch in the software of the 737 Max jet during a technical review, according to a person familiar with the matter.
The company said in a statement that it was “making necessary updates and working with the [Federal Aviation Administration] on submission of this change, and keeping our customers and suppliers informed”.
The software was part of a system that starts when the aircraft powers up and checks that the jet’s other systems are operating correctly, according to the person. During the technical review, Boeing found that one of the checks to monitor other systems did not start correctly.
The technical review was required to help identify and fix problems such as this one, the person said.
The 737 Max has been grounded since March following two crashes in a five-month span that killed 346 people. A flight control system known as the Manoeuvring Characteristics Augmentation System, or MCAS, could push down the nose of a plane based on input from a single sensor. The software was meant to help pilots avoid a stall, but it has been implicated in the crashes.
It is not unusual for problems to surface when a plane is scrutinised during development and testing, said Kevin Michaels, managing director of Aerodynamic Advisory.
The bigger question is how the problem will affect the date the Max returns to service. The FAA must sign off on the jet before it returns to the skies. Even if the US regulatory agency authorises the jet to return to the skies this spring, Mr Michaels said: “You’ve got these wickets to go through at the airlines to get these things back in service.”
Boeing reversed direction last week and recommended simulator training for Max pilots, which means airlines will need to secure two to four hours of simulator time for each one of their thousands of pilots.
American Airlines, Southwest Airlines and United Airlines have removed the plane from their flight schedules until June.
Also on Friday, Fitch Ratings downgraded Boeing’s long-term rating to A- from A, citing “continued regulatory risk regarding the timing and global sequencing of the 737 Max’s return-to-commercial service” as well as the challenge of catching up on deliveries and potential damage to the supply chain while production is halted.
Boeing shares closed 2.4 per cent lower at $324.15 on Friday.