The US Federal Aviation Administration is expected on Wednesday to detail the changes Boeing Co must make on its 737 MAX jet in order for it to fly again commercially following a 20-month grounding sparked by two fatal crashes. In accidents in Ethiopia in 2019 and Indonesia in 2018, a stall-prevention system known as MCAS, triggered by faulty data from a single airflow sensor, repeatedly and forcefully shoved down the jet’s nose as the pilots struggled to regain control.

After a series of investigations and regulatory reviews, here are the major changes the FAA is expected to mandate before the 737 MAX returns to the sky.

SOFTWARE

Boeing’s Maneuvering Characteristics Augmentation System, known as MCAS, will now rely on readings from two Angle of Attack (AoA) sensors that measure the angle at which the wing slices through the air, instead of just one.

MCAS will activate only if both sensors are in agreement, and it will activate only one time, Boeing has said.

Separately, Boeing is making standard an alarm alerting pilots to a mismatch of flight data from the sensors.

Boeing did not tell US regulators for more than a year that it inadvertently made the so-called AoA Disagree alert optional on the 737 MAX, instead of standard as on earlier 737s. Boeing has said the missing display represented no safety risk, an FAA official said in May 2019.

WIRING BUNDLES

Boeing said it will separate 737 MAX wiring bundles, flagged by regulators as potentially dangerous, before the jet returns to service.

The jet’s wiring raised the potential of a short circuit that, in certain remote circumstances, could lead to a crash if pilots did not react in time.

One industry source said the wiring separation was ”still continuing” this week.

FOREIGN OBJECT DEBRIS

In February, Boeing said it found ”foreign object debris” – an industrial term for rags, tools, metal shavings and other materials left behind by workers during production – in the fuel tanks of dozens of undelivered 737 MAX jets.

Boeing said it has inspected all of the stored aircraft and ”shared inspection recommendations and detailed instructions with customers storing their own airplanes.”

First Published:Nov 18, 2020 9:33 AM IST