The National Transportation Safety Board (NTSB) has released its final report on an altitude deviation event involving a United Airlines Boeing 777. The incident occurred shortly after the aircraft’s departure from Kahului, Hawaii on December 18, 2022.
Probable Cause Determination
The NTSB investigation into the incident has identified the probable cause as the failure of the flight crew to effectively manage crucial flight parameters. These included the airplane’s vertical flightpath, airspeed, and pitch attitude. The mismanagement was rooted in a miscommunication regarding the desired flap setting by the aircraft’s captain during the initial climb phase.
Flight Details and Incident Sequence
United Airlines flight UA1722 Kahului – San Francisco
United Airlines flight UA1722 was a scheduled flight between Kahului (OGG) and San Francisco (OGG) operated by a Boeing 777-200 registered N212UA. The airplane experienced a serious loss of altitude approximately one minute after takeoff. This unexpected descent transpired while the aircraft was navigating through instrument meteorological conditions (IMC), characterized by heavy rain.
The altitude loss brought the airplane from a safe 2,100 feet to just 748 feet above the water. Fortunately, the flight crew was able to assess the situation and recover control. No injuries or damage occurred during the incident under report.
The aircraft’s captain was acting as Pilot Flying (PF), and had initially planned for a takeoff with flaps set to 20 degrees and reduced thrust.
However, ground controllers informed the crew of low-level windshear advisories during taxiing, prompting the captain to opt for a takeoff with maximum thrust and flaps set at 20 degrees. The aircraft lifted off, and while the rotation and initial climb were routine, turbulence caused airspeed fluctuations as it ascended.
Critical Moments in the Climb
As the aircraft continued its ascent, the flight crew noticed further airspeed fluctuations due to turbulence. Upon reaching the acceleration altitude, the captain called for a reduction in pitch attitude and a switch to flaps 5.
However, a miscommunication occurred when the first officer, acting as Pilot Monitoring (PM), thought he heard “flaps 15” instead. Acting on this, he set the flaps to 15 degrees before discussing weather conditions with the departure controller.
Airspeed Control Challenges
The captain’s difficulties in airspeed control prompted him to manually reduce engine thrust to prevent a flap overspeed. During this time, he realized that the flap indicator was displaying 15 degrees.
He reissued the command for flaps 5 and confirmed the first officer’s adjustment. The first officer, noticing the captain’s struggle, wondered if his own instrumentation was incorrect. As the situation escalated, the aircraft’s pitch attitude dropped, and airspeed increased.
GPWS Alerts and Recovery Efforts
Both pilots heard warnings from the Ground Proximity Warning System (GPWS) as the situation deteriorated. The first officer recalled announcing “pull up pull up” alongside the GPWS alerts.
In response, the captain pulled back on the control column, reduced power to decrease airspeed, and then applied full power to initiate a recovery from a controlled flight into terrain (CFIT) scenario.
As the captain initiated the recovery, the descent trend began to reverse, signaled by another GPWS alert. Data indicated that this reversal occurred at an altitude of approximately 748 feet above the water.
With a positive climb rate established, the captain adjusted the aircraft’s pitch, retracted the flaps and speed brakes, and engaged the autopilot. The remainder of the flight proceeded without incident.
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