Pilots have reported issues in U.S. with new Boeing jet

Airline pilots on at least two U.S. flights have reported that an automated system seemed to cause their Boeing 737 Max planes to tilt down suddenly.

The pilots said that soon after engaging the autopilot on Boeing 737 Max 8 planes, the nose tilted down sharply. In both cases, they recovered quickly after disconnecting the autopilot.

As described by the pilots, however, the problem did not appear related to a new automated anti-stall system that is suspected of contributing to a deadly October crash in Indonesia.

The Max 8 is at the center of a growing global ban by more than 40 countries following a second fatal crash, this time in Ethiopia, in less than five months. In the U.S., however, the Federal Aviation Administration and airlines continued to permit the planes to fly.

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

The pilot reports were filed last year in a data base compiled by NASA. They are voluntary safety reports and do not publicly reveal the names of pilots, the airlines or the location of the incidents.

It was unclear whether the accounts led to any actions 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," 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. "Best guess from me is airspeed fluctuation" due to a brief weather system overwhelming the plane's automation.

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 460 meters) per minute. 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.

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Air Force One, a heavily modified Boeing 747, is seen prior to US President Barack Obama departure from Andrews Air Force Base in Maryland, December 6, 2016, as he travels to Tampa, Florida, to speak about counterterrorism and visit with troops. / AFP / SAUL LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)
Old airplanes, including Boeing 747-400s, are stored in the desert in Victorville, California March 13, 2015. Last year, there were zero orders placed by commercial airlines for new Boeing 747s or Airbus A380s, reflecting a fundamental shift in the industry toward smaller, twin-engine planes. Smaller planes cost less to fly than the stately, four-engine jumbos, which can carry as many as 525 passengers. Picture taken March 13, 2015. To match Insight AEROSPACE-JUMBO REUTERS/Lucy Nicholson
Old airplanes, including Boeing 747-400s, are stored in the desert in Victorville, California March 13, 2015. Last year, there were zero orders placed by commercial airlines for new Boeing 747s or Airbus A380s, reflecting a fundamental shift in the industry toward smaller, twin-engine planes. Smaller planes cost less to fly than the stately, four-engine jumbos, which can carry as many as 525 passengers. Picture taken March 13, 2015. To match Insight AEROSPACE-JUMBO REUTERS/Lucy Nicholson
Boeing 747 also known as a jumbo jet lines up on a runway in preparation for takeoff.
Old airplanes, including British Airways Boeing 747-400s and FedEx planes, are stored in the desert in Victorville, California March 13, 2015. Last year, there were zero orders placed by commercial airlines for new Boeing 747s or Airbus A380s, reflecting a fundamental shift in the industry toward smaller, twin-engine planes. Smaller planes cost less to fly than the stately, four-engine jumbos, which can carry as many as 525 passengers. Picture taken March 13, 2015. To match Insight AEROSPACE-JUMBO REUTERS/Lucy Nicholson
Old airplanes, including British Airways and Air New Zealand Boeing 747-400s, are stored in the desert in Victorville, California March 13, 2015. Last year, there were zero orders placed by commercial airlines for new Boeing 747s or Airbus A380s, reflecting a fundamental shift in the industry toward smaller, twin-engine planes. Smaller planes cost less to fly than the stately, four-engine jumbos, which can carry as many as 525 passengers. Picture taken March 13, 2015. To match Insight AEROSPACE-JUMBO REUTERS/Lucy Nicholson
VLADIVOSTOK, RUSSIA - JUNE 10, 2016: Deicing Rossiya Airlines' Boeing 747-400 EI-XLJ Vladivostok aircraft at a city airport. Rossiya Airlines launched Moscow-Vladivostok-Moscow services on May 31, 2016. Yuri Smityuk/TASS (Photo by Yuri Smityuk\TASS via Getty Images)
Space Shuttle Discovery rides piggyback atop a specially modified Boeing 747 as it departs runway 22 at Edwards Air Force Base in California on its ferry flight back to Kennedy Space Center in Florida August 19, 2005. Discovery began the return journey to its Florida home port from its landing site in California on Friday after having to land at Edwards Air Force base because of thunderstorms at Cape Canaveral. REUTERS/Tom Rogers TR/HK/KS
The interior of Saudi Prince Alwaleed bin Talal's private Boeing 747 airplane in Riyadh, Saudi Arabia, on Tuesday, April 27, 2010. Alwaleed said he will continue working with Goldman Sachs Group Inc. after the U.S. regulator sued the most profitable securities firm in Wall Street history for misleading its investors. Photographer: Waseem Obaidi/Bloomberg via Getty Images
UNITED STATES - JANUARY 18: Interior of the business class section of the life-size display of the new Boeing 747-8 Intercontinental in Renton, Washington, Thursday, Jan. 18, 2007. The plane is a stretched version of the current 747-400 and incorporates interior featured from the 777 and the upcoming 787. (Photo by Kevin P. Casey/Bloomberg via Getty Images)
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Preliminary information released by Indonesian investigators suggests they are looking at the possible role of the Max's new automated anti-stall technology as a factor in a Lion Air crash in October shortly after takeoff from Jakarta. Data indicates 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 — called MCAS for its acronym — 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 spokesman Ross Feinstein said the airline has 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 9 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, added, "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 seemed to be abating but returned on Sunday when an Ethiopian Airlines Max 8 crashed shortly after takeoff from Addis Ababa, killing all 157 people on board. Again, preliminary data appears to capture a brief and erratic flight. Investigators will analyze information from the planes so-called black boxes in hopes of understanding what caused the accident.

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