The 737 Max will not fly commercially this year. Ian Taylor reports.

The grounded Boeing 737 Max will not return to airline schedules until next year despite Boeing’s assertion last week that it is on course to return by December.

Boeing chief executive Denis Muilenberg testified before a US Congressional committee this week having admitted in a letter to the committee: “We made mistakes and got things wrong.”

His company was accused of “inexcusable” behaviour by the chair of the committee Peter DeFazio on Wednesday, with DeFazio insisting new evidence showed the aircraft maker had rushed development of the 737 Max.

The aircraft was grounded in mid-March following two disasters in five months which killed 346 passengers and crew.

An automated flight control system (MCAS) designed to prevent stalling has been implicated in both crashes, its faults exacerbated by the inadequate information given to pilots.

Documents released by Congress this week suggested Boeing was aware that a failure of the MCAS anti-stall system on the Max could be “catastrophic” if pilots did not respond within 10 seconds.

Yet the company downplayed the importance of the system and seemed keen to minimise the pilot training required.

DeFazio told Boeing chief executive Dennis Muilenburg: “This was inexplicable and inexcusable. A variety of decisions could have made those planes safer.”

Boeing had claimed pilots would not need additional training to fly the Max and to understand the MCAS system.

The Congressional committee also released a complaint from a senior manager at Boeing which suggested workers on the Max were “exhausted” by the pace of work on the aircraft.

In an email, the manager confessed: “I’m hesitant about putting my family on a Boeing aeroplane.”

The committee is expected to recommend toughening the process of aircraft certification by the US Federal Aviation Administration (FAA) after DeFazio said: “Complacency set in on the manufacturers’ side and the regulator’s side.”

Boeing insisted last week it expects the Max’s return to be signed off by the FAA before the end of this year.

However, Boeing has yet to complete testing of the software update to the MCAS system which it hopes will get the Max flying and the FAA has yet to schedule a certification flight.

The FAA review following the flight would be expected to take a month. Only when the FAA certifies the Max as airworthy would the MCAS software fix and pilot training be rolled out.

It is expected to take at least six weeks from certification to get the first of the 385 grounded aircraft into service, with each having to undergo a series of tests.

Relations between the FAA and Boeing were soured by the disclosure on October 18 of previously unreleased text messages from 2016 by the former chief test pilot for the Max which described the air craft’s anti-stall system “running rampant” on a simulator.

The pilot reported the aircraft “trimming itself like crazy”, referred to “Jedi-mind tricking regulators” and admitted: “I lied to the regulators (unknowingly).”

The head of the FAA rebuked Boeing for failing to reveal the messages earlier.

There is also uncertainty about whether other aviation regulators will follow the FAA’s lead without concluding their own checks.

A Joint Authorities Technical Review issued by representatives of nine aviation regulators this month criticised aspects of FAA guidance, and Europe’s aviation safety agency (EASA) told the FAA it was not satisfied with demonstrations of the reconfigured systems on the Max.

A report by Indonesian investigators into the first of the crashes by a Lion Air 737 Max, published last week, concluded a series of failures by Boeing, Lion Air and the pilots led to the disaster and suggested the aircraft should not have been flying.

When the Max does return, airlines then face a battle to convince passengers to board. United Airlines has already confirmed it will give passengers the option of not flying on the Max.

Two US consumer surveys in June suggested 70% of passengers would hesitate to book a Max flight and only 14% would fly the aircraft within six months of its return. A poll of corporate travel managers suggested two in three corporate travellers would change their plans to avoid flying the Max.

Boeing also faces lawsuits from victims’ families which threaten to fuel public concerns.