Originally Posted by
fire wall
Fortunate to have flown all 3
GEnX is my pick, it just delivers.
Eng Ice Crystal Icing events a concern but suspect much the same for all power plants.
Interested to hear your thoughts on this tdtracer.
I assume you mean the CF6-80C2 (unless you've also flown the 747-8)?
Ice Crystal Icing (ICI) is an interesting phenomenon. Our understanding of ICI is way better than it was 30+ years ago when it first raised it's ugly head on the CF6-80C2, but I still wouldn't say that it's well understood. For the uninitiated, 'conventional' icing involves super-cooled liquid water droplets - liquid water that is well below freezing so it's just looking for something to freeze to like a nice cold wing or inlet leading edge. It's readily addressed by adding heat to the susceptible surfaces. ICI is fundamentally different - ICI is literally very small ice crystals - and they simply bounce off cold surfaces. BUT, warm surfaces can present an issue - the IC hit the warm surface and melt. If the ice crystals are present in sufficient quantities, additional crystals hit the liquid water and cool it sufficiently that it re-freezes - resulting in ice accumulation on surfaces that would normally be considered way too warm to ice. In testing, we saw ice accumulation in areas of the compressor where the air temp was as high as 85 deg F/30 deg C!
There seems to be something about the GE compressor design practices that make it more prone to ICI than Pratt or RR. For a long time, the CF6-80C2 was the only engine that had issues with ICI, although eventually the PW2000 suffered a few ICI events (but nowhere near as bad as the CF6. The GE90 had minor issues with ICI (no shutdowns, but some minor compressor damage events) but ICI hit the GEnx hard. We had a 747-8/GEnx-2B event fairly early on that - although the engines re-lit and ran fine for the balance of the flight, there was severe compressor damage on 3 engines. GE came up with a fairly ingenious method of detecting the presence of ICI and opening the compressor bleeds to send most of the ice overboard and that effectively solved the ICI issue with the GEnx.