The head of the US air safety agency faces harsh questions from senators Wednesday over its relationship with and oversight of Boeing, while the aerospace giant launches a charm offensive to try to restore its reputation after two air disasters in recent months killed 346 people.
Dan Elwell, acting head of the Federal Aviation Administration that sets standards for air safety around the world, will have to explain why the FAA delayed grounding the Boeing 737 MAX fleet after the Ethiopian Airlines tragedy, in which a MAX 8 crashed shortly after takeoff near Addis Ababa on March 10, killing 157 people.
The delay gave rise to suspicions of a too-cozy relationship between regulators and the American aircraft manufacturer, especially since Chinese and European authorities moved quickly to ban the planes due to the similarities with the October 29 crash in Indonesia of another 737 MAX 8, that time operated by Lion Air.
Boeing chief Dennis Muilenburg will be absent from the Senate hearing Wednesday but is expected to be called at a later date.
Ahead of this day of reckoning, the company launched a campaign to convince the flying public that it is addressing the issues with the MAX, including a fix to the Maneuvering Characteristics Augmentation System (MCAS) stall prevention system implicated in the crashes.
Many journalists and pilots and airline officials were invited to Boeing's massive factory in Renton, Washington in the Pacific Northwest, to unveil the software changes and offer reassurances.
The FAA, which delegates some certification procedures to Boeing, including parts of the MAX, nevertheless was "directly involved" in the safety review of the MCAS, Elwell said in his prepared testimony, obtained by AFP.
"FAA engineers and flight test pilots were involved in the MCAS operational evaluation flight test," he will tell senators at the hearing, which begins at 3:00 pm (1900 GMT).
"The certification process was detailed and thorough," but "time yields more data" to be used to evaluate new products, which is what happened with the MAX, he added.
And Elwell acknowledged that as systems become more complex, the FAA's "oversight approach needs to evolve."
In the wake of the accidents and amid intense scrutiny, Boeing is racing to get the MAX back in the sky.
The company held tests flights Monday using the upgraded MCAS, following flight simulator tests Saturday.
The MCAS, which makes the aircraft dive when necessary in order to regain speed if it detects a stall or loss of airspeed, was developed specifically for the 737 MAX, which has a heavier engine than its predecessor, the 737 NG.
Boeing said the final version of the fix should be submitted to the FAA "at the end of the week," according to a company official.
Among the changes, the MCAS will no longer repeatedly make corrections when the pilot tries to regain control and will be automatically disconnected in the event of disagreements between the two "angle of attack" sensors, two sources close to the matter told AFP.
This is a major change because until the Ethiopian Airlines tragedy, the MCAS was set to react to information from a single sensor and would repeatedly override pilot corrections.
The initial investigation into the Lion Air crash found that one of the AOA sensors failed but continued to transmit erroneous information to the MCAS.
Boeing also will install a warning feature -- at no cost --- called a "disagree light" to indicate to the pilot when the AOA sensors are out of sync.
The FAA chief must also assure senators that regulators will not fast track the MAX's return to the skies.
"The 737 MAX will return to service for US carriers and in US airspace only when the FAA's analysis of the facts and technical data indicate that it is appropriate," he said.