Engine stall. On 25 August 2010, a Boeing 757-200 being operated by UK airline Astraeus on a passenger flight from Freetown Sierra Leone to London Heathrow was in the cruise at night in IMC at FL370 when vibration levels on both engines increased. When the prescribed ice shedding drill was followed, one engine malfunctioned and vibration on the other remained abnormally high and so a MAYDAY was declared and a diversion to Nouakchott, Mauritania was made without further event. None of the 103 occupants were injured and there was no engine damage.