Two Boeing 737 MAX 8 pilots reported nosedives after engaging autopilot in 2018, data reveals
North American carriers such as Southwest Airlines have defended the 737 MAX’s safety. (Flickr: Paul Thompson)
Airline pilots on at least two US flights have reported that an automated system seemed to cause their Boeing 737 MAX 8 planes to tilt down suddenly.
- Two pilots separately reported to NASA that they suspected automated controls in their Boeing 737 MAX planes were faulty
- Both planes suddenly tilted mid-flight but were quickly corrected
- North American carriers have continued to fly the 737 MAX, despite groundings elsewhere
In reports filed last year in a database compiled by NASA, the pilots said that soon after engaging the autopilot on their planes, the nose tilted down sharply.
In both cases they recovered quickly after disconnecting the autopilot, they said.
The problem as described by the pilots, however, did not appear related to a new automated anti-stall system that was suspected of contributing to a deadly October crash in Indonesia.
Americans hold out
The MAX 8 is at the centre of a widening ban — now involving more than 40 countries — following a second fatal crash, this time in Ethiopia, in less than five months.
In the US, however, the Federal Aviation Administration (FAA) and respective carriers continue to permit the planes to fly.
Overnight US President Donald Trump said modern planes were “too complex to fly”, and a Reuters source claimed the US President spoke to Boeing CEO Dennis Muilenburg after his comments.
American Airlines and Southwest Airlines operate the 737 MAX 8, and United Airlines flies a slightly larger version, the MAX 9.
All three carriers vouched for the safety of MAX aircraft on Wednesday.
Unclear if reports led to FAA action
Groundings by country:
- European Union
- United Arab Emirates
- United Kingdom
The pilot reports were voluntary and did not publicly reveal the names of the pilots, the airlines or the location of the incidents.
It was unclear whether the accounts led to any action by the FAA or the pilots’ airlines.
In one report, an airline captain said that immediately after putting the plane on autopilot the co-pilot called out “descending”, which was followed by an audio cockpit warning, “Don’t sink, don’t sink!”
The captain immediately disconnected the autopilot and resumed climbing.
“With the concerns with the MAX 8 nose down stuff, we both thought it appropriate to bring it to your attention,” the captain wrote.
The captain added that the “best guess from me is airspeed fluctuation” due to a brief weather system overwhelming the plane’s automation.
Low-altitude warning system was blamed in both reports
Newer versions of Boeing’s 737 series have incorporated greater automated controls. (Flickr: Frans Zwart)
On another flight, the co-pilot said that seconds after engaging the autopilot, the nose pitched downward and the plane began descending at 1,200 to 1,500 feet (365 to 457 metres) per minute.
@Flightradar24 tweet: Additional data from Flightradar24 ADS-B network show that vertical speed was unstable after take off.
As in the other flight, the plane’s low-altitude-warning system issued an audio warning.
The captain disconnected autopilot and the plane began to climb.
The pilots talked it over later, “but can’t think of any reason the aircraft would pitch nose down so aggressively”, the co-pilot recounted.
Preliminary information released by Indonesian investigators suggested they were looking at the possible role of the MAX’s automated anti-stall technology as a factor in a Lion Air crash in October shortly after take-off from Jakarta.
Data indicated that the pilots struggled with repeated nose-down commands from the plane before it crashed into the Java Sea and killed 189 people.
However, that anti-stall system — known by its acronym MCAS — only activates if the autopilot is turned off, according to documents Boeing has shared with airlines and the FAA.
“That’s not to say it’s not a problem,” American Airlines pilot Dennis Tajer said of the incidents reported to NASA, “but it is not the MCAS. The autopilot has to be off for MCAS to kick in.”
American Airlines spokesperson Ross Feinstein said the airline had received no reports from pilots about problems with the anti-stall technology. Southwest has said the same thing.
Leaders of the union representing United Airlines pilots, some of whom have flown the airline’s 14 Boeing 737 MAX series jets since last May, said the airline has tracked 23,000 hours of flights and found no performance or mechanical problems.
The group, part of the Air Line Pilots Association, warned against sensationalism in light of the crash:
“It is imperative that pilots refrain from interacting with the media and adding to the sensationalism surrounding these incidents.”
Concern about the MAX’s safety returned on Sunday when an Ethiopian Airlines MAX 8 crashed shortly after take-off from Addis Ababa, killing all 157 people on board.
The jet showed an unstable vertical speed after take-off, air traffic monitor Flightradar24 said, and the senior Ethiopian pilot sent out a distress call.
Investigators will analyse information from the plane’s so-called black boxes in hopes of understanding what caused the accident.