Boeing holds test flights for 737 MAX after crashes

Boeing's fleet of 737 MAX planes has been grounded since Mar 13 following two fatal crashes. (AFP/STEPHEN BRASHEAR)

The aviation giant, which has been under fire and its flagship narrow-body planes grounded since Mar 13, tested the system upgrade on Monday, two days after pilots from American Airlines did simulation flights in Renton, Washington, the sources said.

Boeing needs authorisation from the Federal Aviation Administration before the MAX can return to service. But the company still has not submitted its proposed software patch to the FAA, a government source told AFP.

The aircraft was grounded following two deadly accidents involving Ethiopian Airlines earlier this month and Lion Air in October which killed 346 people.

Engineers have been focusing on addressing problems with the MCAS system, a stall prevention system designed to point the nose of the 737 MAX 8 downward if it is in danger of stalling, or losing lift.

The system has been criticised since it can malfunction, and make it difficult for pilots to control the aircraft. Both of the recent crashes occurred moments after takeoff.

The MCAS, or Maneuvering Characteristics Augmentation System, was installed in the MAX because they are heavier than in the previous version of the 737.

Boeing remains under intense pressure following the two crashes, which will be the subject of a Senate hearing Wednesday. A company spokesperson declined to comment, but said the company is in regular contact with regulators.

Preliminary results in the investigation into October's Lion Air crash in Indonesia indicate a single "angle of attack" sensor, which feeds data to the MCAS, malfunctioned but continued transmitting data to the plane's flight systems, including the MCAS.

Among the changes to the system, the MCAS would automatically be disabled in cases where there is disagreement between two sensors, the sources told AFP.

Boeing also intends to make standard on planes a "disagree light", to signal when the MCAS malfunctions. The feature currently is only available to airlines for an additional charge.

FAA TO FACE CONGRESS

A Senate Commerce Committee panel will hold a hearing on Wednesday to question FAA Acting Administration Daniel Elwell and Transportation Department Inspector General Calvin Scovel. The session is expected to be followed by a second hearing at a later date with Boeing, airline pilots and other stakeholders, the committee said.

The officials are expected to face questions from lawmakers on the FAA's certification of the 737 MAX and whether regulators have become too cozy with the company, and fast-tracked some approvals

Boeing will be "carefully monitoring" the testimony, the company said.

"Boeing continues to support the ongoing accident investigations, and is working with the authorities to evaluate new information as it becomes available," the company said. "Safety is our top priority when we design, build, deliver and maintain Boeing aircraft."

The FAA is expected to defend its practices, including the delegation of key testing and certification to Boeing in light of tight government budgets, said Scott Hamilton an aviation expert with Leeham Company.

Lawmakers could push the FAA to pledge rigorous oversight before allowing the 737 MAX to return to service.

"Frankly, I think Congress itself should be testifying on its decades of underfunding the FAA to do its job of overseeing the aerospace industry (as well as modernising Air Traffic Control)," he said. "But it won't take this responsibility."

Scovell likely will be asked what he has learned so far in the DOT's investigation into the FAA certification of the 737 MAX, which was requested by Transportation Secretary Elaine Chao.

Chao sought the audit to develop "an objective and detailed factual history" of the process of certifying the aircraft," she said in a memo to Scovel last week.