descent in icing conditions

[jorgvaz]

hi, could anybody help me on this topic?

Operating CFM 56 engines idle RPM equipped, but without

Minimum Engine Speed Control system, during descent in icing

conditions, is necesary to maintain a minimum engine speed of

45% N1 in order to increase the engine tolerance to water

ingestion?

Thanks in advance for your help!:confused:

[Mad (Flt) Scientist]

Rather than to deal with water ingestion (which would be a factor in "visible moisture" rather than "icing") I suspect the minimum idle speed is specified to provide enough engine bleed air for the engine and airframe anti-ice systems.

[BlueEagle]

Many moons ago an Air Europe B737-300, with the CFM56 engine, had a double flame out due to water (very heavy rain) ingestion up near Thessaloniki in Greece. Fortunately they got them both started again.

Engineers familiar with the 737-300 may remember if a 'fix' was then issued or if operating procedures were changed?

[RHLMcG]

My recollection is that there were several 737 incidents in the early to mid 80s including one involving a deadstick landing.

Shortly thereafter a procedural change came out from Boeing requiring minimum RPMs for flight in heavy rain (bit long ago for my memory but 45 percent N1 lingers in the back of my head). Didn't seem to cause any problem other than those associated with unexpected heavy rain during descent requiring spin up and subsequent profile control problems. My recollection of the justification is along the lines of increasing the mass airflow to a level sufficient to prevent the deluge of water putting out the fires.

[lomapaseo]

The above covered the potential for water/ice/hail ingestion in descent quite well. However, there is still another less seriouo concern in icing conditions. That is at very low fan RPMs the blades themselves will ice up creating imbalance in all engines of concern to the crew.

This happens more often during ground operations and can be handled quite nicely by informed crews spooling up now and then to shed the ice during taxi. Unfortunately, if you do this in a flight environment it is considered a distraction by the Feds and not permitted under the icing rules FAR33 (the engine may not damage itself nor require pilot input while operating in icing conditions) Thus an automatic system was employed in an attempt to be completely transparant to the crew.

[seat 0A]

The problems with water ingestion were cured by installing modified spinners, somwhere in `92 or `93.

[B737CL/NG_Mech]

definetly yes, the CFM 56-3 Engine once had an front cone spinner. The spinner was redesigned to an ellyptical type. Now the inertia of the water/ice causes it not to enter the compressor section when deflected on the spinner.

yours,

[mono]

I've seen pics of a KC-10 carrying water instead of fuel 'flying the boom' to direct water directly into the engine inlet (CFM 56) and that is where the ellipsiod spinner was derived.

Don't know where to find the pics now but they were spectacular!!

:D :D