Software link suspected in Airbus A220 engine blowouts
On the CF6-80C2 we had pilots turn on Anti-Ice, but it was for indirect effects. First off, at least on the Boeing installations, turning on anti-ice increases the idle speed (the CF6-80C2 ICI issue was typically during an idle descent - ice would accumulate in the compressor then shed when they accelerated to level off and the ice shed would quench the combustor - so higher idle was goodness). Second, the extra bleed for anti-ice made the engine run 'richer' which provided better flameout protection when the ice shed.
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They are trying to keep the fan shaft (really the LP compressor) out of a speed/flow condition that, with the recently implemented different stator vane schedule, puts an LP compressor blade stage into resonance. I suspect the reason for the anti-ice restriction at high altitude is that anti-ice puts a heavy bleed load on the engine, changes the flow/speed relationship within the compressor, and gets them into resonance as well. If they allowed anti-ice bleed at high altitude they'd have to further reduce the fan speed limit I suspect. High altitude climb is where fan speeds are typically highest, and reducing the allowed fan speed there is a heavy performance penalty.
So would they even be able to make FL350 at typical weight using 94%? That wouldn’t work for the aircraft that I've flown, but perhaps the values are different for this engine?
They are trying to keep the fan shaft (really the LP compressor) out of a speed/flow condition that, with the recently implemented different stator vane schedule, puts an LP compressor blade stage into resonance. I suspect the reason for the anti-ice restriction at high altitude is that anti-ice puts a heavy bleed load on the engine, changes the flow/speed relationship within the compressor, and gets them into resonance as well. If they allowed anti-ice bleed at high altitude they'd have to further reduce the fan speed limit I suspect. High altitude climb is where fan speeds are typically highest, and reducing the allowed fan speed there is a heavy performance penalty.
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I don't understand your comment because I'm not sure how pilot-to-engine-control interaction came into this. Could you elaborate or restate it please?
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Agreed - having the selection of anti-ice cause an engine failure in a very short period of time would create a threat of common cause failure of both engines on the same flight, and shouldn't be acceptable. I don't know how long this particular engine can withstand the resonance issue that is occurring, but I've seen some compressor blade vibration issues where it takes dozens of flights before the issue (a bent blade from ice impact in the case I'm thinking of) causes the blade to fail. This issue may be a case where the failure results from the cumulative exposure from a large number of flights, in which case probability of failure of both engines on the same flight from common mode failure is much lower. Again, while I'm aware that this is a blade resonance issue in part due to a vane schedule change, I don't have detailed knowledge of the issue and am speculating on the details.
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What Differences ??
I am wondering what might be the difference in engines on the BTI and LX fleet of A 220. While the former - according FlightRadar24 - operate the entire flight envelope of the a/c type, the latter still crawls around at altitudes not higher than 29000 ft. Any explanation ?
I am wondering what might be the difference in engines on the BTI and LX fleet of A 220. While the former - according FlightRadar24 - operate the entire flight envelope of the a/c type, the latter still crawls around at altitudes not higher than 29000 ft. Any explanation ?
