FAA proposes replacement of P&W 4000-series electronic engine controls

The FAA is proposing that US operators of 730 PW4000-series engines with 94in (239cm) fan diameter inspect, identify and, over time, replace certain defective electronic engine controls (EEC) on each engine.

Aircraft models powered by PW4000 engines with those diameters include Airbus A300s/A310s, and Boeing MD-11, 767-200s/300s and 747-400s.

The proposed airworthiness directive, issued today, is the result of a May 2006 in-flight shutdown of a Pratt & Whitney PW4152 turbofan due to defective EEC pulse-width modulator (PWM) microcircuits that degraded over time, says the FAA.

Investigators determined that the dual redundant circuits were defective when built and both failed over time due to thermal cycling within the certified operating temperature range of the engines.

"Based on a risk analysis provided by P&W which we reviewed and concurred, this condition, if not corrected, could result in uncommanded in-flight engine shutdowns, which could result in loss of thrust and prevent continued safe flight or landing," says FAA.

The FAA says the defective PWMs "are the result of a change from the original PWM design introduced by a single microcircuit supplier before 1993", adding that the manufacturer returned to the previous, correct designs between 1993 and 1994.

The FAA estimates the work will take one work-hour per engine to inspect, categorize, and mark each of the 730 EECs, and one work-hour per engine to replace as many 730 EECs over a period of one to six years, depending on the results of the inspections. Estimated total cost to U.S. operators of $467,200.

Source: Air Transport Intelligence news

Fonte: Flight Safety Information 19/08/2008.