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Links between 737 MAX crashes – and mention of stairs

March 19, 2019 Headline News No Comments Email Email

Preliminary analysis of data retrieved from doomed Ethiopian Airlines flight ET 302 has revealed disturbing similarities to the October 2018 crash of Lion Air flight JT 610.

Ethiopian Transport Minister Dagmawit Moges said yesterday: “The cause of the crash was similar to that of Indonesia’s flight 610.” She added that detailed analysis would be made public in a month.

The information still needs to be verified and the investigation is in its early stages.

Aviation Week says Moges’s statement suggests that the two 737 MAX 8 accidents (both planes were nearly brand new) may be linked to a flight control issue. The MAX’s manoeuvring characteristics augmentation system (MCAS) flight-control, mentioned by many analysts, automatically trims the horizontal stabilisers nose-down when it detects the plane’s “angle of attack” is too high.

Ethiopian Airlines ET 302 was airborne for just six minutes before plunging into the ground, killing all 157 people on the flight on Sunday 10 March 2019. Lion Air flight JT 610 slammed into the Java Sea 13 minutes after takeoff from Jakarta on 29 October 2018, killing all 189 passengers and crew.

Both of the 737 MAX 8 aircraft that crashed experienced fluctuations in speed and altitude in the early stage of the flight after takeoff, possibly because MCAS kept trying to push the 737 MAX 8’s nose down while the pilots responded with nose-up commands.

Whether this is true or not will hopefully be revealed in coming weeks. In the meantime, the 737 MAX 8 and 9 fleet remains grounded worldwide, 371 aircraft in all.

MEANWHILE, an intriguing theory focuses on a set of folding stairs incorporated in the original 737 design in the 1960s.

One of the flight recorders retreived from the crashed Ethiopian Airlines flight ET 302

Ralph Vartabedian, an aerospace and defence writer with the Los Angeles Times, says the Boeing 737-100, first introduced in West Germany as a commuter jet in the early Cold War era, had folding metal stairs attached to the fuselage that passengers climbed to board. This was before airports had aerobridges and when ground crews lifted luggage into the cargo hold by hand.

The 737’s low-to-the-ground design was an advantage in 1968 and suited the plane’s retractable stairs – but, according to Vartabedian, engineers modernising the 737 have had to work around the design ever since, even though the retractable stairs have gone.

The first versions of the 737 in the 1960s had thin engines shaped like cigars that were well clear of the tarmac – but engines have got bigger since, taking up more space between the underside of the wing, where they are fitted, and the tarmac beneath.

To handle a longer fuselage and more passengers, Boeing added larger, more powerful engines. That, Vartabedian says, required Boeing to reposition the engines to maintain sufficient ground clearance.

“As a result, the 737 can pitch up under certain circumstances,” Vartabedian writes, and MCAS software was added to counteract that tendency. His article, complete with diagrams, appears here in the Los Angeles Times.

Additionally, the Seattle Times has reported that it has learned from “current and former engineers directly involved with the evaluations or familiar with the document” that Boeing’s safety analysis of MCAS had several crucial flaws, including understating the power of the system.

Vartabedian acknowledges that a software fix or additional pilot training may turn out to be all that’s needed to fix any 737 MAX problem. The 737 is the most successful commercial jet ever produced.

Written by Peter Needham

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