American Airlines took a Boeing 737 MAX out of service on Monday after it experienced a pitch trim issue enroute from Miami to Santo Domingo in the Dominican Republic.
Flight AA98 with 135 passengers (out of 172 capacity) and six crew members was flying at around 33,000 feet just south of Nassau in the Bahamas “when the crew reported a pitch trim issue, pitch trim failure and decided to return to Miami.” Fifty minutes later it touched down safely. A replacement Boeing 737 MAX operated the flight to Santo Domingo.
The occurrence aircraft, registration N302SA, was delivered to American two weeks before the MAX’s grounding in March 2019. It was taken out of service and is currently scheduled to operate from Miami to St. Croix on Wednesday. The FAA intends to investigate.
An American Airlines spokesperson tells me,
American Airlines flight 987, with service from Miami (MIA) to Santo Domingo, Dominican Republic (SDQ), reported a possible mechanical issue after departing MIA on March 29. The aircraft landed safely at MIA without incident and taxied to the gate on its own power. All customers deplaned normally, and there were no reported injuries to any customers or crew. A replacement aircraft was used to fly our customers to SDQ while our maintenance team evaluated the original aircraft.
At this point we have little detail on exactly what happened, and what the pilots experienced, although it appears that a component of the trim system failed which was not related to the MCAS system.
A ‘pitch trim’ incident raises flags with the Boeing 737 MAX because it immediately brings to mind the issues that grounded the aircraft for nearly two years. In both the fatal Lion Air and Ethiopian Airlines crashes, runaway trim was caused when faulty angle of attack readings caused the aircraft’s MCAS computer system to move the horizontal stabilizer and push the plane’s nose down. Here the pilots would have manually trimmed the aircraft.
The 737 MAX now compares data from both of its angle of attack sensors and if there’s a material difference between the sensors then the MCAS system will be inhibited throughout the flight. The system also only now activates once per incident, eliminating repetitive nose-down pitch. Runaway stab trim is inhibited automatically, no longer requiring use of a non-normal checklist. And pilots have received explicit training on the issues that occurred with the MAX previously.
Ultimately the pilots of the aircraft remained in control and landed safely. The system worked as it should. Extra attention, though, will be likely paid to this incident because it involved elevator trim and the MAX, even though it doesn’t appear to have involved the MCAS system.