History of Flight
On September 22, 2022, about 1200 Pacific daylight time, Hawaiian Airlines flight 3, an Airbus A330-243 (N393HA), encountered a pitch trim anomaly while climbing out of Los Angeles International Airport (LAX) in Los Angeles, California. The flight crew declared an emergency and returned to LAX without further incident. None of the 12 crewmembers or 278 passengers were injured, and the airplane sustained no damage. The flight was a regularly scheduled domestic passenger flight from LAX to Daniel K. Inouye International Airport, Honolulu, Hawaii, operating under 14 CFR Part 121.
While climbing through flight level 360, the trimmable horizontal stabilizer (THS) control wheel began moving rapidly forward and aft, causing small pitch oscillations. No alerts annunciated on the electronic centralized aircraft monitor or flight deck. The crew disengaged the autopilot, and the trim wheel continued erratic movement but did not affect flight control or stability. Re-engaging the autopilot caused the oscillations to resume. The first officer, who was pilot flying, kept the autopilot off and manually flew for the remainder of the flight.
The crew contacted air traffic control (ATC) to report a flight control anomaly and intention to return to LAX. They informed flight attendants and requested an A330 captain traveling in the cabin to assist. Maintenance control in Honolulu was contacted; they suggested a primary computer reset, but the quick reference handbook indicated that reset should only be performed on the ground. The traveling captain and an A330 first officer in the cockpit jumpseat could not find a relevant procedure. The crew declared an emergency, requested fuel jettison vectors, and managed the situation with all four pilots coordinating tasks. Fuel was jettisoned to reach maximum landing weight, and the airplane landed uneventfully on runway 24L.
Aircraft Information
Pitch control is provided by two elevators on the trailing edge of the THS. The THS moves hydromechanically via a ball screw actuator powered by two hydraulic motors and held by brakes. The THS actuator operates in electrical mode (auto trim) or manual mode. Mechanical control is via two flight deck trim wheels connected by cables to the actuator's mechanical input shaft. The pitch trim actuator, a subcomponent of the THS actuator, has three DC motors, each with its own controller and digital electronic module. Position feedback is provided by command (COM) and monitor (MON) rotary variable differential transformers (RVDTs).
System Testing
The incident THS actuator was examined at Collins Aerospace in France. No significant damage was found. It passed acceptance test procedures with no faults, including operational checks at positions recorded during the incident. The pitch trim actuator, when tested, showed microswitch movement and internal friction torque beyond component maintenance manual (CMM) limits, but Airbus stated these were unrelated to the observed behavior. The No. 1 digital electronic module, active during the incident, was tested at Triumph Aerospace. It passed isolation, bonding, and automatic tests but failed a leakage test (pressure below CMM limit); Airbus stated this was unrelated. Attempts to replicate the oscillation by testing a resolver-to-digital converter microchip were unsuccessful. The module's circuit boards showed no anomalies under microscopic and X-ray examination. The COM RVDT pack from the incident was also tested; no faults were found, though ground continuity exceeded CMM limits (deemed typical by Collins). The MON RVDT from the incident had been repaired before testing could be performed.
Post-Incident Events
After the incident, the pitch trim actuator was replaced. Subsequent flights in October and November 2022 experienced other flight control faults, leading to replacement of additional components, including a flight control primary computer, RVDTs, and another pitch trim actuator. On November 7, a STAB drift fault occurred on a flight from LAX to Kahului, Hawaii, where recorded data showed a drift in MON RVDT sensed position while THS position remained stable. No THS oscillations were reported during these events, and as of the report date, no similar pitch trim faults had been reported on the airplane.