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               Congressional
          -Research Service






Boeing 737 MAX Crashes Shake Confidence

in International Air Safety



March 14, 2019

Recent foreign air disasters involving Boeing 737 Max airplanes have raised international concern about
the safety of that aircraft and passenger airline safety in general. On October 29, 2018, Lion Air flight 610
crashed shortly after departure from Jakarta, Indonesia, killing all 189 on board. While the investigation
of the crash is still ongoing, it has been disclosed that pilots flying the same aircraft the previous day
experienced some sort of navigation system failure and that maintenance records revealed ongoing
problems with the aircraft's airspeed and angle-of-attack (AOA) sensors that monitor relative aircraft
pitch. Aviation experts expressed concerns that faulty indications from these sensors could cause the
aircraft's flight automation to command a pitch-down response. The investigation also revealed that
aircraft documentation and pilot training may not have fully explained how the automation would respond
under these circumstances. On March 10, 2019, Ethiopian Airlines flight 302 crashed shortly after
departure from Addis Ababa, Ethiopia, reportedly resulting in 157 fatalities.
The circumstances of these crashes led several airlines and several countries, including China and the
European Union, to immediately ground 737 MAX  airplanes until a fix can be found to revise flight
control software or otherwise address flight control difficulties that may have contributed to these crashes.
Initially, the Federal Aviation Administration (FAA), Boeing, and U.S. air carriers did not follow suit. One
day after the Ethiopian Airlines crash, FAA instead gave notification to international civil aviation
authorities anticipating mandatory design changes to be forthcoming no later than April 2019. However,
on March  13, 2019, President Trump announced that FAA would issue an emergency order grounding all
737 MAX   aircraft.
Noting external reports identifying similarities between the two crashes, FAA has focused on the AOA
sensors and flight control logic contained in a Maneuvering Characteristics Augmentation System
(MCAS),  a flight control feature that is new to the 737 MAX. On November 7, 2018, FAA issued an
emergency directive ordering U.S. operators of Boeing 737 MAX aircraft to apply runaway stabilizer
procedures in situations potentially arising from erroneous high AOA indications that might trigger
repeated nose-down trim commands by the MCAS.  In December 2018, FAA expanded the scope of the
airworthiness directive, ordering the procedural change for all Boeing 737 MAX airplanes worldwide.
Currently, three U.S. airlines fly 74 737 MAX aircraft, including the 737 MAX 8 variant involved in both
crashes and the slightly larger 737 MAX 9 variant, both of which are covered under the emergency

                                                                  Congressional Research Service
                                                                    https://crsreports.congress.gov
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