What happened
The aircraft had been parked overnight on the ramp, uncovered, during continuous rain. Following takeoff in heavy rain, the aircraft reached a cruise altitude of FL250. While operating in instrument meteorological conditions (IMC) with an outside air temperature of -20 degrees Celsius and light rime icing, the crew experienced engine power interruptions in both engines. Simultaneously, all airspeed indications decreased to zero. The flight crew initiated a descent and declared an emergency, eventually landing the aircraft safely at its destination. No injuries were reported.
The investigation
The investigation revealed that engine power interruptions under light icing conditions had been occurring since this aircraft type entered revenue service. Previous Airworthiness Directives (ADs) had been issued to prohibit revenue flights and later to restrict flights in icing conditions unless equipped with an auto ignition system.
Engine manufacturers determined that ice or slush could accumulate on the inlet particle separator, break off, and enter the engine, causing a flameout. This accumulation of ice/slush was not visible to pilots and was not mitigated by the engine anti-ice system. An auto ignition system had since been added to the aircraft to restart engines within two seconds of such an event.