Two cabin crew members on a Ryanair flight fell to the floor and one broke an ankle after the pilot pulled too hard on the aircraft's manual controls when it began to "overspeed" during a descent in a jetstream.
The Boeing 737-8AS registered to Ryanair in Dublin was descending into Manchester Airport on the evening of January 14th, 2017, when the incident occurred, according to a report by the UK's Air Accidents Investigation Branch (AAIB).
It said that while descending into a high altitude jetstream, an associated rise in headwind caused the aircraft to overspeed.
“The commander disengaged the autopilot and used manual control inputs to stop the speed increasing, but in doing so applied a significant nose-up pitch input on the control column. The resulting manoeuvre caused two cabin crew members to fall, and one of them sustained a broken ankle. The operator (Ryanair) has issued additional guidance to its pilots regarding overspeed recognition and recovery,” the report said.
The 31-year-old commander, who had flown 4,997 total flight hours, reported that “because the autopilot appeared not to be correcting the condition, and thinking that he had little time to react, he simultaneously pressed the autopilot disengage button on his control wheel and pulled back on the control column”.
“His intention was to avoid the overspeed as smoothly as possible using manual control inputs.”
Force changed
The investigation found there were “marked changes in the normal acceleration of the aircraft over a short period”. Technical data showed that in the one second during which the autopilot was disengaged, the force exerted on the control column by the pilot changed from -0.51 lbs to +42.76 lbs.
“The commander reported that he was aware of the possibility of encountering a jetstream in the descent, but had not seen the airspeed increase to this extent before,” the report said.
He suspected that a phenomenon known as “startle effect” had caused him to exert more force on the control column than intended. This effect is described as a reflex action elicited by exposure to a “sudden, intense event that violates a pilot’s expectations”.
Since the incident, both pilots on the flight had undergone simulator training focused on overspeed recovery, the AAIB said.
Boeing, the aircraft manufacturer, had also indicated it was aware of other similar occurrences.
In March 2017, a Boeing 737 encountered an increasing headwind during descent which resulted in indications that the aircraft would overspeed, the report said.
The pilot in control responded with a manual control input which caused the autopilot to disengage. Two cabin crew members suffered injuries during the resulting aircraft manoeuvre.
The commander on the January 2017 flight told the investigators he had learned from the experience, particularly in relation to the handling sensitivities of the aircraft at high altitudes.
In its conclusions, the investigation body said the serious injuries suffered by a cabin crew member occurred “because significant manual control inputs were applied in response to an impending overspeed, which resulted in the aircraft manoeuvring abruptly”.
“An increasing headwind associated with a jetstream had caused the airspeed to rise. The narrow speed margins and handling sensitivities of the aircraft at high altitudes were contributory factors.”
Boeing said it was considering a revision to the overspeed guidance in the 737 flight crew training manual.