By Elan Head | November 28, 2013 Estimated reading time 2 minutes, 49 seconds.
Prompted by incidents of ice crystal icing (ICI) at high altitudes, the United States Federal Aviation Administration (FAA) has issued an Airworthiness Directive (AD) for Boeing Model 747-8, 747-8F and 787-8 airplanes powered by General Electric GEnx engines.
The AD, which is effective immediately, prohibits operation in moderate and severe ICI conditions. It also requires inspection of the engine after any ICI event is detected by the flight crew.
Over the past decade, incidents of ICI have prompted the release of ADs on various airplane models equipped with General Electric CF6-80 engines. A type of icing that does not appear on radar due to its low reflectivity, ICI can lead to ice crystals accumulating in the core gas flow path of the engine. In previous events, this ice has shed during throttle transients and in the descent phase of flight, causing temporary thrust loss.
However, the incidents that prompted the new AD — all of which occurred during 2013 — were more serious, occurring during the cruise phase of flight and causing permanent damage to the engine compressor in addition to loss of thrust. The events occurred on 747-8, 747-8F and 787-8 airplanes, during cruise flight at 33,000 feet or above. All of the events occurred either within or after the airplane traversed a large mesoscale convective system — an area where several thunderstorms had merged, driving a significant quantity of moisture in the form of ice crystals up to or above the tropopause.
After evaluating the incidents, the FAA concluded that the threat posed by ICI warranted immediate action. “Unrecoverable thrust loss on multiple engines, due to operation in high altitude clouds containing ice crystals, could lead to a forced landing,” it states in the AD.
The FAA describes the AD as an “interim action,” with further rulemaking to be considered if a final action is later identified. As reported by Reuters, General Electric said it had a software fix for the engine that it will put into effect early next year.
To read the complete AD on the FAA website, click here.
