United States and European regulators knew at least two years before a Lion Air crash that the usual method for controlling the Boeing 737 MAX’s nose angle might not work in conditions similar to those in two recent disasters, a document shows.
The European Aviation and Space Agency (EASA) certified the plane as safe in part because it said additional procedures and training would “clearly explain” to pilots the “unusual” situations.
The unusual situation in which they would need to manipulate a rarely used manual wheel to control, or “trim,” the plane’s angle.
Those situations, however, were not listed in the flight manual, according to a copy from American Airlines.
The undated EASA certification document, available online, was issued in February 2016, an agency spokesman said.
It specifically noted that at speeds greater than 230 knots (265mph, 425kph) with flaps retracted, pilots might have to use the wheel in the cockpit’s centre console rather than an electric thumb switch on the control yoke.
EASA and the U.S. Federal Aviation Administration (FAA) ultimately determined that set-up was safe enough for the plane to be certified, with the European agency citing training plans and the relative rarity of conditions requiring the trim wheel.
In the deadly Lion Air crash in October, the pilots lost control after initially countering the Maneuvering Characteristics Augmentation System (MCAS), a new automated anti-stall feature that was pushing the nose down based on data from a faulty sensor, according to a preliminary report from Indonesian investigators released in November.
The flight conditions were similar to those described in the EASA document, a source at Lion Air said.
The source said that training materials before the crash did not say the wheel could be required under those conditions but that Boeing advised the airline about it after the crash.
Boeing declined to comment on the EASA document or its advice to Lion Air, citing the ongoing investigation into the crash.
Ethiopia’s Transport Ministry, France’s BEA air accident authority and the FAA have all pointed to similarities between the Lion Air crash and an Ethiopian Airlines disaster this month.
But safety officials stress that the Ethiopian investigation is at an early stage.
The crashes have also heightened scrutiny of the certification and pilot training for the latest model of Boeing Co’s best-selling workhorse narrowbody, now grounded globally.
In the EASA document, the regulator said simulations showed the electric thumb switches could not keep the 737 MAX properly trimmed under certain conditions, including those of the Lion Air and Ethiopian Airlines crashes, according to the Indonesian preliminary report and a source with knowledge of the Ethiopian air traffic control recordings.
The trim system adjusts the angle of the nose. If the nose is too far up, the jet risks entering a stall.
Additional procedures and training needed to “clearly explain” when the manual wheel might be needed, according to the document.
The EASA spokesman said that was a reference to the Boeing flight crew operations manual.
An American Airlines Group Inc flight manual for 737 MAX pilots dated October 2017 said the thumb switches had less ability to move the nose than the manual wheel.
The manual, which is 1,400 pages long, did not specify the flight conditions in which the wheel might be needed.
The trim wheel is a relic of the Boeing 737’s 1960s origins and does not appear in more modern planes like the 787 and Airbus SE A350.
“It would be very unusual to use the trim wheel in flight. I have only used manual trim once in the simulator,” said a 737 pilot.
“It is not physically easy to make large trim changes to correct, say, an MCAS input. You – or more than likely the other pilot – have to flip out a little handle and wind, much like a boat winch.”
The EASA document said that after flight testing, the FAA’s Transport Airplane Directorate, which oversees design approvals and modifications, was concerned about whether the 737 MAX systems complied with regulations because the thumb switches could not control trim on their own in all conditions.
A trim-related “equivalent level of safety” (ELOS) memorandum listed in its 737 MAX certification document is not available on the FAA website.