Draft AC Offers OEMs Guidance on Induction Icing

 - September 2, 2010, 12:24 PM

The FAA yesterday issued Draft Advisory Circular 20-147A, which provides new guidance to aircraft manufacturers on compliance with regulations covering engine induction system icing and engine installation ice requirements. The new guidance will replace AC20-147A, which was last revised in 2004. Comments on the draft AC are due by November 1 and can be sent to the FAA's John Fisher. One of the key changes in the draft AC is mixed phase or ice crystal icing conditions, which "has caused more than 100 turbine engine power losses," according to the FAA. These conditions "occur when supercooled liquid water droplets and ice particles coexist in a cloud, often around the outskirts of a deep convective cloud formation." This is the first time the FAA has introduced compliance methodologies for these conditions and is likely a response to instances of power rollback that have caused engine flameouts. Indeed, the AC goes on to state that the aviation industry believed that turbine engine susceptibility to mixed phase or ice crystal conditions was "minimally consequential" with the exception of pronounced inlet bends and high-solidity, high-turning front-stage compressor stators. The FAA is also recommending that ice-detection systems be evaluated for TAT probe malfunctions during icing events.