The U.S. Federal Aviation Administration ordered the temporary grounding of the Boeing 737 MAX family operated by U.S. airlines or in U.S. territory on March 13. Earlier in the day, President Donald Trump announced the plan to ground the aircraft, a move that the FAA had said it had decided against the day before despite the growing number of international civil aviation authorities around the world that had grounded the aircraft.
The agency noted in a statement that it had made the decision after looking at new satellite data showing similarities between the flight profiles of Ethiopian Airlines Flight 302 and Lion Air Flight JT610, which crashed last year on October 29.
Both crashes involved the 737 MAX 8, an upgraded and re-engined version of Boeing’s 737-800 narrowbody family. The investigation into the Lion Air crash has yet to be completed, but investigators have focused on the new anti-stall feature of the 737 MAX family’s automated flight control system. Boeing added this system, known as the Maneuvering Characteristics Augmentation System (MCAS), to the MAX variants to improve aircraft handling and decrease pitch-up tendency at elevated angles of attack, such as those that could lead the aircraft’s wings to stall. The system does not operate during normal flight; it kicks in only when the aircraft enters a non-normal part of the operating envelope.
Initial reports indicated that a faulty angle-of-attack sensor fed the automated flight control system erroneous information, leading the system to repeatedly lower the nose of the aircraft into a dive to prevent what it determined would be a dangerous stall. Boeing tested the system during its flight test campaign prior to certification, but the Lion Air pilots may not have understood how it affected the aircraft’s controls prior to the crash. A lack of sufficient training on the workings of the new system, and how to disable it during an emergency, may also have played a role in the crash.
The lack of a final report from investigators on the Flight JT610 has complicated the response of regulators to the Ethiopian Airlines crash. It is extremely rare for two brand new, recently certificated airliners to crash within five months of each other. Without knowing for sure why the first aircraft crashed, investigators cannot be sure whether Flight 302 crashed for the same reason. Regulators overseas were the first to adopt the cautious approach, with a string of countries grounding the aircraft in their jurisdictions. Press coverage in the United States questioning the safety of the MAX family turned the FAA’s response to the two crashes into a political issue, capturing President Trump’s attention and increasing the pressure on the FAA to act.
Since the Lion Air crash, Boeing has been working on an update to the MCAS flight control law. The new law alters AOA inputs, limits stabilizer trim commands in response to an erroneous angle of attack reading, and limits the stabilizer command to leave elevator authority in the hands of the pilot. Other changes include revised pilot displays, operation manuals and crew training.
Boeing has yet to announce any disruption to its production schedule, and our forecast assumes that the factory will continue to turn out aircraft even if airlines suspend or defer deliveries while waiting for safety regulators to approve any necessary changes to the MAX’s system and for Boeing to implement them prior to delivery. The manufacturer is planning to increase production this year from the current 52 aircraft per month to 57 aircraft per month, and there is a risk that the changes required to the MAX family are so extensive that Boeing’s production schedule is significantly disrupted. The longer it takes to determine why both Flight JT610 and Flight 302 crashed, the more likely it is that customers will defer deliveries this year.
Over the long term, we expect there to be little impact on the outlook for the MAX family. The aircraft’s main competitor, the Airbus A320 family, has a massive backlog of orders, and Airbus doesn’t have enough open production slots to handle a surge of defecting Boeing customers. Our 10-year forecast for the 737 is unchanged at this point, but that outlook assumes that Boeing can rectify any technical or training flaws that investigators identify.