US investigators determined that two passengers on a united Boeing 757-200 suffered a fracture after the crew responded to a dispute warning with a “sudden” pitch input.
The National Road Safety Commission says the two cabin crews were also suffered minor injuries during the incident.
The aircraft was being driven from Newark to San Francisco on September 19th last year.
According to the assistant officer who was flying, the captain was still waiting for clearance to a lower altitude, in preparation for the possibility that he had to turn on the “detention seat belt” sign near the top of the descent, and then descend quickly.
After descending and leveling at 32,000 feet, the jet was cleared to 31,000 feet, but the flight exceeded the desired vertical flight path, so the assistant officer used the “change flight level” mode to increase the descent rate.
Approximately 500 feet above the assigned altitude, the crew received traffic recommendations from the collision avoidance system. Advisory related to aircraft crossing 1,500 feet below the 757.
Traffic Advisory was upgraded to Resolution Advisory as the first mate adjusted the descent rate by switching to “Vertical Speed” mode. This is an instruction to avoid the action.
According to the captain's testimony to the Safety Commission, “The incredible factor in the (resolution recommendation) was very high due to the speed at which it occurred (after the initial traffic alert).”
The first mate responded by removing the autopilot and autorottle and pitching the aircraft's nose-up using guidance from the primary flight display.
Recorded flight data shows that the aircraft's pitch increased by 3° in space of 1 second – from 1.76° to a nose-up of 2.81° – stop the descent. The normal force ranged from 2.3g to 0.6g in 2 seconds.
The “seat belt” sign was on, but some passengers were not back in their seats before piloting.
One passenger of the posterior cleanser maintained a spinal vertebrae fracture in the lumbar. Another passenger left the bathroom and swayed upwards likewise, breaking his ankle as he landed.
Two cabin crew members in the galley ahead fell to the floor while piloting, causing minor injuries.
After the aircraft (N12125) landed on San Francisco's runway 28L, paramedics met the flight at Gate F21 and carried the injured passenger to the hospital.
