Investigators believe a SriLankan Airlines Airbus A330-300 lost significant altitude mid-flight after one of the pilots nudged a side stick during cruise, disconnecting the autopilot and forcing the jet into a descent.
While the inquiry does not specify the reason for the “sharp nose-down entry” by the first flight officer, it refers to the fact that he was served food but did not hand over control of the aircraft to the co-pilot – a cruise pilot. in the left seat, which represented the resting captain.
The plane was cruising at 39,000 feet above the Indian Ocean, west of Jakarta, during a flight from Colombo to Sydney on March 21 last year.
After about 3 hours of flight, the captain went to rest in the cabin and the excursion pilot moved from the right seat to the captain’s left seat. He acted as the monitor pilot while the assistant first officer took over as the pilot in the right seat.
The incident occurred minutes after the changeover to the euro.
Analysis shows that the first officer’s side stick deflected nose down for several seconds, sufficient to trigger an involuntary autopilot disengagement and generate the main warning.
The twinjet went from 2.8° nose up to 1.1° nose down and began to descend.
It was operating in reduced vertical separation minimum airspace, where the cruising altitudes of adjacent aircraft are only 1,000 feet apart.
The cruise pilot, although not designated as the flying pilot, responded by engaging the autopilot, but without indicating that he was taking over. The first officer continued to operate the side controller, causing the autopilot to disengage again.
Investigators add that the cruise pilot was “shocked” by the changes in airspeed and “observed” neither vertical speed nor altitude loss.
The aircraft reached a nose-down pitch of 5.3° and descended at up to 5,700 ft/min, losing 1,540 ft before the first officer’s side stick released and the cruise pilot’s side stick registered a nose-up entry. The autopilot was subsequently re-engaged and the aircraft recovered about 2 minutes after the initial disturbance and climbed back to its assigned altitude.
Neither pilot followed specific procedures for handing over or taking over control of the aircraft, the inquiry said.
“The excursion pilot and the first officer as operational flight crew did not demonstrate the expected level of competence,” he adds. “There was poor crew coordination during the incident.
Although the cruise pilot informed air traffic control in Jakarta of the altitude deviation, the pilots did not fully inform the captain after returning to the cockpit. The cruise pilot did not engage the first officer in the discussion, briefed the captain in Sinhala – the non-accepted aviation language – and did not mention the exact extent of the altitude loss.
The seriousness of the incident was only discovered during routine monitoring of flight data.
Mandatory incident reports were filed on April 2, nearly two weeks after the incident, and all three crew members were immediately grounded pending an investigation.
Both the flight data recorder and the cockpit voice recorder had already been overwritten by this point and the query had to rely on information from the digital access recorder.
None of the passengers – only nine passengers and seven crew members – were injured and the aircraft (4R-ALR) was undamaged.
The investigators recommended improved turbulence recovery training and awareness of incident reporting criteria, particularly for loss of altitude in RVSM airspace. SriLankan Airlines, the query adds, should put in place procedures for handing over control of the aircraft when serving meals.