Irish investigators believe engine icing on a departing McDonnell Douglas DC-8-63 freighter caused compressor stalls in both left-hand engines, prompting the crew to shut one powerplant down and return for an emergency landing.

The aircraft, operated by US carrier Murray Air on the Shannon-Doha route, had been climbing through 900ft in conditions "probably conducive" to engine ice formation, says the Irish Air Accident Investigation Unit.

Its engine anti-ice systems were not active during the climb and the outboard left-hand Pratt & Whitney JT3D engine experienced a compressor stall. The crew shut the engine down as a precaution, and called for an emergency return to Shannon, only for the inboard left-hand engine then to suffer a similar problem.

The crew started running through the four-engine failure checklist and, because the minimum-control airspeed for simultaneous loss of same-side engines was 208kt, began descending rapidly - at 2,600ft/min, down to 1,100ft - to maintain airspeed.

As part of the four-engine failure procedure the crew turned on the engine anti-ice. The engines subsequently stabilised, and the crew managed to restart the stopped powerplant before conducting an uneventful, albeit overweight, landing at Shannon.

Investigators concluded that rapid icing of the engine nacelles led to the problem. In the wake of the 28 March incident last year, the carrier - now known as National Airlines - changed its procedures to urge crews to use engine anti-ice during departure in certain cold-weather conditions.

Source: Air Transport Intelligence news