Two years after the catastrophic crash of a Boeing 737 MAX jet in Indonesia touched off an aviation crisis, the Federal Aviation Administration today laid out the path for hundreds of 737s to return to flight.
But that can’t happen immediately: It’ll take months for the FAA to check the implementation of changes in pilot training procedures, and verify all the fixes that will be made. All 737 MAX planes have been grounded worldwide in the aftermath of a second crash that occurred in Ethiopia in March 2019.
“This is not the end of this safety journey,” FAA Administrator Steve Dickson told CNBC. “There’s a lot of work that the airlines and the FAA and Boeing will have to do in the coming weeks and months.”
Stan Deal, president and CEO of Boeing Commercial Airplanes, said in a news release that today’s FAA directive was an “important milestone” but agreed that there’s a lot of work still to be done. “We will continue to work with regulators around the world and our customers to return the airplane back into service worldwide,” Deal said.
The key fixes involve software rather than hardware — and that part of the job is more like installing a Windows update than installing an actuator.
Based on months of investigation, it was software that led to the fatal flaw in the jets that crashed. The design changes that were made for the next-generation 737 MAX planes, changed the planes’ aerodynamic characteristics. To make things simple and reduce the costs involved in retraining pilots, Boeing added a software enhancement — known as the Maneuvering Characteristics Augmentation System, or MCAS. That enhancement changed the flight software to make flying the 737 MAX more like flying older 737s.
The MCAS system is said to account for only a few lines of code, embedded in the millions of lines that make up the 737’s flight control software. Unfortunately, the MCAS left the software vulnerable to a glitch involving the plane’s angle-of-attack sensors. If one of the two angle-of-attack sensors provided bad readings, there was a chance that the autonomous system would force the plane into a hard-to-control dive. Investigators say that’s what led to the crashes..
While the 737 MAX planes were grounded, Boeing worked on software fixes to ensure that the MCAS system would kick in only when both sensors signaled a problem — and even then, the system would kick in only once, rather than repeatedly. Other fixes provide more cross-checking between computers.
It’s taken months for the FAA to verify that the fixes will resolve the software problem to its satisfaction, and that pilots will be adequately trained to deal with any issues that arise during flight. In the course of reviewing the work, additional safety issues came up. For instance, the review team identified a potential fault condition that could lead to a runaway situation with the 737 MAX’s horizontal stabilizer.
“Although this condition has never occurred during the 200 million hours of flight operations on any 737 airplane, new software was developed, tested and certified to ensure that it can never happen,” Boeing said in its FAQ about the return to flight.
The flight software was also modified to head off the possibility that the autopilot could disengage without a pilot command — a theoretical scenario that’s never actually occurred.
The FAA is also requiring changes that provide more separation in the wiring for the horizontal stabilizer control system. “In some cases, we will perform this task for our airline customers; in others, we’ll provide them with all of the technical documentation and materials they need to do the work themselves,” Boeing said.
Now it’s up to Boeing and the airlines to install the software and have the fixes verified electronically by the FAA. They’ll also have to make the wiring changes, and go through detailed maintenance procedures to get planes that have been stored for more than a year ready for flight again.
All that will take much longer than installing a Windows update.
“It’s a complete software load installation for the Flight Control Computer software and the software for the cockpit display system,” Bjorn Fehrm, an analyst for Leeham News ana Analysis, told GeekWire in an email.
For security reasons, the installation isn’t done wirelessly. Engineers need physical access to each aircraft, and the software package is transferred manually from a data storage device after the proper codes are entered, Fehrm said.
“In total you need about 500 man-hours per aircraft to install all software patches, control these as correctly loaded and do the separation changes to the wiring demanded by the FAA in the rear of the aircraft,” he said.
Boeing estimates that just over half of the more than 800 grounded 737-8 and 737-9 planes have not yet been delivered and are still at Boeing. Half of those planes are due to be delivered by the end of next year, and the majority of the remaining planes are to be delivered in 2022.