US air safety officials have announced that they will look into the circumstances surrounding how a Boeing 777 jet unexpectedly lost altitude and almost crashed into the Pacific Ocean.
On December 18, United Airlines flight 1722 departed Maui and was ascending when it abruptly descended 1,400 feet (425 metres), according to reports.
It stabilised at a height of just 775 feet before safely landing in San Francisco 27 minutes ahead of schedule.
It adds to a string of close calls involving aircraft this year.
According to the aviation website Flightradar24, the flight was proceeding normally until 71 seconds after takeoff from Kahului Airport, when it abruptly lost altitude.
The National Transportation Safety Board (NTSB), which investigates US plane crashes, will produce a report about the incident within three weeks.
Passenger Rod Williams told CNN: “There were a number of screams on the plane. Everybody knew that something was out of the ordinary, or at least that this was not normal.”
He said it was “sobering” to think they were probably about five seconds away from hitting the water.
A United Airlines representative told BBC News that the flight’s pilots filed an internal safety report after landing. They have a combined 25,000 hours of flying experience.
An investigation by the airline resulted in additional training for the pilots, which United said was ongoing.
“Safety remains our highest priority,” a company official said in a statement.
The Federal Aviation Administration (FAA) also received a report of the incident and “took appropriate action.” It did not elaborate.
The incident is among a number of potentially dangerous events reported by US airlines recently, including two near misses in New York and Texas this year.
The NTSB is already looking into two close calls within the last month.
On 4 February, a FedEx cargo plane aborted its landing to avoid a Southwest Airlines plane at Austin-Bergstrom International Airport in Texas.
At John F. Kennedy International Airport in New York in January, a Delta flight stopped short on the runway during takeoff to avoid an American Airlines plane.