BOEING HAS warned operators of 757s about several engine-rundown incidents on aircraft powered by Rolls-Royce RB.211-535E4 s. About half of the 700 aircraft operated by some 60 airlines across the world are involved, but the indications are that only older examples are affected.
According to the US manufacturer, six incidents have occurred at the top of descent when engine thrust is reduced to low idle under autothrottle command, and one during acceleration from low idle. In addition, seven events have occurred after selection of engine anti-ice on between 30,000ft (9,150m) and 25,000ft in descent. All are reported to have taken place during adverse weather conditions, and particularly in potential icing conditions.
In a few instances, the remaining engine was found to have suffered a concurrent core-compressor stall. Although R-R refuses to comment, it is understood that modifications are being developed to increase the compressor stall margins through improvements to the bleed valve-control unit and the fuel-flow governor, but these will take some months to be implemented.
Boeing says that it advised operators of the issue in December, and it is "...working with Rolls-Royce to resolve it".
Airlines have initiated operating procedures to minimise the possibilities of further rundowns of one, or both, engines. These include selecting engine anti-ice on before entering icing conditions, and bringing one engine to stabilised high idle before selecting anti-ice on the second engine. Capt Bob Screen, flight-operations director at 757 operator Air 2000, however, suggests that the potential danger should not be overstated, as the RB.211 has a "superb in-flight re-lighting capability".
Source: Flight International