Air Canada is probing an incident in which an Airbus A320 lost thrust on one engine as is passed through a mountain wave en route to Los Angeles.
The aircraft, with 146 passengers and five crew members, was operating from Toronto on 27 January, says the Transportation Safety Board of Canada.
It says the A320 (C-FLSS) was cruising at 36,000ft some 85nm southwest of Colorado Springs, in the Rocky Mountains region.
The aircraft passed through a mountain wave, oscillations in the atmosphere caused when air current flow is disturbed over high terrain.
Its left-hand CFM International CFM56 powerplant rolled back, says the board, from 90% of N1 to 60%.
"The aircraft started to lose speed, and started to [descend]," it adds. The crew informed air traffic control of the situation, requesting a change in cruise altitude to 30,000ft, but no emergency was declared.
While the left-hand engine showed "slight vibration", says the board, there was no alert from the aircraft’s centralised monitoring system. The engine recovered shortly afterwards and the aircraft landed without further incident.
Air Canada is assessing the event in an effort to establish the cause, says the safety board.