Pressure mounted on Boeing Co in Washington as US lawmakers called for executives to testify about two crashed 737 MAX jets, even as the world's biggest planemaker worked to return the grounded fleet to the skies.
A Senate panel plans to schedule a hearing with Boeing at an unspecified date, officials said, the first time a US congressional committee has called the company's executives to appear for questioning over the crashes.
The same panel, the Senate Commerce subcommittee on aviation and space, will also question FAA officials on March 27, likely about why the regulator agreed to certify the MAX planes in March 2017 without requiring extensive additional training.
The Ethiopian Airlines crash on March 10 that killed all 157 on board has set off one of the widest investigations in aviation history. Initial reports from investigators say there are clear similarities between the crash and the Lion Air accident that killed all 189 crew and passengers in November.
While no direct link has yet been established, the MCAS flight control software and related pilot training are at the centre of the investigation, and US lawmakers are questioning the Federal Aviation Administration's certification of MAX's safety.
Boeing has promised a swift update to the MCAS, and the FAA said the installation of new software and related training was a priority.
However, extra computer-based training will be required after the software update, the pilot union of MAX's biggest customer, Southwest Airlines Co, said on Wednesday, becoming the first major airline union to comment.
The Southwest Airlines Pilots' Association said it had previewed the proposed Boeing training, including a required test, which would be mandatory for Southwest pilots before flying the 737 MAX again.
A Boeing spokeswoman said training on the software update would be provided by the manufacturer, but declined to disclose further details.
Regulators in Europe and Canada have said, however, they will seek their own guarantees of the MAX's safety.
MOUNTING SCRUTINY
The Ethiopian Airlines crash has shaken the global aviation industry and cast a shadow over the Boeing model intended to be a standard for decades to come.
Investigators examining the Lion Air crash are weighing how the MCAS system ordered the plane to dive in response to data from a faulty sensor and whether the pilots had enough training to respond appropriately to the emergency, among other factors.
MCAS is meant to prevent a loss of lift which can cause an aerodynamic stall and send the plane downwards in an uncontrolled way.
The pilots of the doomed Lion Air flight scrambled through a handbook to understand why the jet was lurching downwards in the final minutes before it hit the water, three people with knowledge of the cockpit voice recorder contents said.
Indonesian investigators have said the cockpit voice recorder information was leaked to the media and they plan to hold a news conference at 0830 GMT on Thursday.
Boeing has said there was a documented procedure to handle the problem.
The company was sued on Wednesday in federal court in Chicago by the estate of one of the Lion Air crash victims in which the plaintiffs referred to the Ethiopian crash to support a wrongful death claim against the company.
A Boeing spokesman said the company does not respond to, or comment on, questions concerning legal matters.
The Seattle Times reported the Federal Bureau of Investigation was joining the investigation into the MAX's certification. An FBI spokeswoman in Seattle would neither confirm nor deny that it was a part of any investigation.
Criminal prosecutors at the US Justice Department, who are also investigating the FAA's oversight of Boeing, have issued multiple subpoenas to Boeing, CNN reported, citing sources briefed on the matter.
Bloomberg said last year US officials started investigating the FAA's approval of the MAX software linked to the Lion Air plane crash last year within weeks after the accident, citing people familiar with the matter.
The Pentagon Inspector General said it would investigate a complaint that Acting US Secretary of Defense Patrick Shanahan, a former Boeing executive, violated ethical rules by allegedly promoting Boeing while in office.
Facing high-profile scrutiny, Boeing reshuffled executives in its commercial airplanes unit to focus on its response.
FINAL MOMENTS
Before the Lion Air flight crashed, sources told Reuters the Indian-born captain, aged 31, was quiet, while the Indonesian officer, 41, said “Allahu Akbar”, or “God is greatest”.
A different crew on the same plane the previous evening had the same situation but resolved it after running through three checklists, though they did not pass on the information to the doomed Indonesian crew, a preliminary report in November said.
As with the Indonesia flight, the Ethiopian crew radioed about control problems shortly after take-off and sought to turn back. Ethiopia's civil aviation head Wosenyeleh Hunegnaw said he expected a report on the investigation within 30 days.
For now, more than 350 MAX aircraft are grounded, and deliveries of nearly 5,000, worth more than $500 billion, are on hold. Boeing's shares have fallen 11 per cent since the Ethiopian Airlines crash, wiping $26 billion from its market value.