The US National Transportation Safety Board (NTSB) has attributed a near-accident off the coast of an Hawaiian island late last year to flightcrew miscommunication.
The 18 December incident involved a San Francisco-bound United Airlines Boeing 777-200ER (N212UA) that descended rapidly to about 800ft above the Pacific Ocean just after take-off before recovering. It was first reported by The Air Current on 12 February.
In its final report, released on 10 August, the NTSB says the probable cause of the incident, in which no-one was injured, was the ”flightcrew’s failure to manage the airplane’s vertical flightpath, airspeed and pitch attitude following a miscommunication about the captain’s desired flap setting during the initial climb.”
Data from flight-tracking website Flightradar24.com, shows United flight 1722’s departure from Maui’s Kahului Municipal airport was normal until 71s after take-off, when the aircraft entered a steep dive. It was tracked as descending from 2,200ft above the Pacific Ocean to under 800ft, before recovering and continuing to San Francisco.
By the time the NTSB had initiated an investigation earlier this year, ”both the cockpit-voice and flight-data recorder durations had been exceeded” and the investigation ”utilised flightcrew statements and other records as information sources”.
The NTSB says that the departure took place in instrument meteorological conditions, which included heavy rain. After the ground controller advised the flightcrew that low-level windshear advisories were in effect, the captain modified the aircraft’s take-off configuration from that originally selected.
”He hand-flew the take-off, with the autothrottles engaged. During the take-off, the rotation and initial climb were normal; however, as the airplane continued to climb, the flightcrew noted airspeed fluctuations as the airplane encountered turbulence.
”When the airplane reached the acceleration altitude, the captain reduced the pitch attitude slightly and called for the flap setting to be reduced to 5 [degrees]. According to the first officer, he thought that he heard the captain announce 15 [degrees], which the first officer selected before contacting the departure controller and discussing the weather conditions.”
The captain reported that this misunderstanding caused the aircraft to react in an unexpected way.
After correcting the error, with the widebody losing altitude and gaining speed, the crew conducted ”the full CFIT [controlled flight into terrain] recovery” to bring the aircraft into a normal flight path.
The rest of the flight proceeded without incident.
”As a result of the event, United Airlines has modified one of its operations training modules to address this occurrence and issued an awareness campaign about flight path management at their training centre,” the NTSB says.
In February, the Federal Aviation Administration (FAA) said the crew did report the incident “as part of a voluntary safety reporting programme”. The agency added that it reviewed the incident and “took appropriate action”, without providing details.
At the time, United said the flightcrew, who have about 25,000h of flying experience among them, “fully co-operated” with the FAA’s investigation, adding that the event led to “the pilots receiving additional training”.