THE CREW of a Loganair flight bound for Sumburgh needed three attempts to regain safe airspeed after ice formed on the plane's wing following take-off from Edinburgh Airport in June last year.
In a report published on Thursday, the Air Accidents Investigation Branch (AAIB) said the Saab 340 with 36 people board suffered significant performance loss during the incident.
Investigators found that the pilots did not "initially address the problem sufficiently".
After departing from Edinburgh at 2.02pm on 5 June, the aircraft initially encountered light turbulence in cloud. This suddenly intensified and ice began to form quickly on the aircraft.
The stick shaker - a warning device - was activated and the autopilot disconnected.
Normal procedure is to manually reduce the pitch attitude to accelerate the aircraft. However, the pilot had to do this three times and eventually descend the aircraft by 500 feet to regain speed.
The AAIB report said: "The severity and extent of ice accumulation on the upper wing surface led to a significant performance loss, which meant the aircraft was unable to maintain the selected airspeed at the aircraft altitude and a descent was necessary to regain lost airspeed."
"The crew actions did not initially address the problem sufficiently and the stick shaker occurred again. Following the third activation of the stick shaker the crew descended the aircraft to regain a safe airspeed.
"Although maximum power was not set, the aircraft did accelerate and the crew were able to clear the icing and turbulent conditions before continuing their fight without further incident."