Avoidance of High Altitude Ice Crystal Icing Conditions – FAA Airworthiness Directive, No 2013/24/01, affecting Boeing 747-8, 747-8F and 787-8 aeroplanes powered by GEnx engines – Potential Implications for ATC
High altitude ice crystal icing (ICI) conditions have been a known threat to the operation of some aircraft engines for a number of years. However, prompted by new reports of engine damage and thrust loss events as a result of flying in high altitude ICI conditions, the United States FAA has recently adopted an airworthiness directive (AD) concerning Boeing 747-8 and 747-8F and 787-8 series aeroplanes powered by GEnx engines. The AD makes mandatory the operating procedures contained in Boeing's previously published operator messages, as well as recently updated Aeroplane Flight Manuals for airplanes with GEnx engines. Specifically, the AD requires aircraft operators to advise flight crews of potential ICI conditions at high altitudes i.e. above 30,000ft, and prohibit operation in moderate and severe ICI conditions.
More definitively, the AD includes immediate mitigating procedures for the affected aircraft which prohibit flight within 50nm of amber and red radar returns that are displayed below the aircraft's flight path during operations at or above 30,000 ft, when approaching, or in, IMC or visible moisture.
Note: Boeing has also published an updated Flight Crew Operations Manual Bulletin with specific operating procedures for flight crews.
Potential Implications for ATC
All 747-8 aircraft and some 787-8s are powered by GEnx engines. ATC will not know which 787s have GEnx engines, so it is impossible for controllers to know when a GEnx 787 or 747-8 is approaching weather conditions that may give rise to ICI. Nevertheless, air traffic controllers should be aware of the potential that if these aircraft types are flying above 30,000ft and they encounter the meteorological conditions described previously, they may need to:
- make larger deviations than other traffic to avoid certain weather – i.e. deviate by at least 50+nm; or
- make even larger reroutes (100 – 150 nm minimum) around groups of thunderstorms/convective weather.
Pilots may also opt to descend below FL300 depending on the circumstances.
Other Remedial Actions
- Boeing is working with its customers and GE to address the ICI issue and remove any operational restrictions; only a small number of GEnx engines have experienced the ice-crystal icing issue in-flight.
- GE will introduce the improvements necessary to return the engines to expected performance levels.
Your Attention is Required
- Air Navigation Service Providers and Aircraft Operators are invited to note the subject, consider the relevance to their operations and share any operational experience.
- Supplementary information including the background rationale for the AD can be found at: FAA AD – Directive No 2013-24-01 effective 27 November 2013.
- Boeing Aero Magazine article: Engine Power Loss in Ice Crystal Conditions
- SKYbrary article: High Level Ice Crystal Icing: Effects on Engines
- EUROCONTROL Safety Alerts: