ulisse

good day
I'm a bus driver and recently I was confused by the meanning of the run up in icing condition

as far as i know if you are experiencing some vibrations during the run up you should assume that the engine(s) are iced and to avoid damage due to ice shedding and ingestion you should keep at idle and return to gate to remove it in another way

any info is appreciated

thanks

lomapaseo

Do a search on this subject in this section and you will find lots of discussion on it

Of course you can return to bay to have the ice removed, however the SOP was developed to avoid this in most cases. The concept assumed that if you do the runup soon/often enough the amount of ice shed will not cause damage

nnc0

We've had a heck of lot of damage due to blade and inlet icing on the ground.

The shedding procedure throws off the ice from the blades via centrifugal force and flexing of the blades. It also serves to scrape away any ice buildup forward of the fan plane as the blades flex forward with application of more power

We've found that in the right conditions (moist snow with lots of slush on the ramp) ice will accumulate in the bottom of the nacelle barrel. At idle rpm, any ice in the plane of the blades will be scraped away. Any snow or ice forward of the fan plane however will simply accumulate and continue to accumulate there if the rpms aren't increased occasionally to flex the plane of the fan forward.and scrape that ice away before the build up becomes significant. If you don't increase the rpm and wait until application of take off power, the plane of the fan will flex forward and the blades will come in contact with whatever chunk of accumulated ice remains there. The damage to the blade tips will be substantial and you'll have a hell of an expensive repair. Ive seen the blade tips bent back 90 degrees or more. Pretty impressive.

Our tests were with CFM 56 engines and Snecma nacelles on A319s/A320/A321s. That the same engine doesn't seem to have any issue when installed on a 737 has me at a loss. I can only assume the nacelle geometry and airflow is slightly different.

I also can't explain why other A320 operators don't seem to have the same issues with tip damage that we do. I can say that our maintenance procedures are deficient in snowstorm conditions (not in compliance with AMM recomendations at least and we don't use covers or heaters, nor do they do a proper tactile inspection upon arrival or prior to departure.) I suspect that may be a major contributing factor

lomapaseo

Fan Blades are designed not to flex forward enough to make a difference. They of course do flex/untwist all of which is accounted for in performance.

If you are picking up bent blade tips than it would be spinner ice at taxi conditions which is supposed to be shed by timely spoolups during taxi before it gets big enough to cause damage. Check your other cold weather operators

Ice sheds on fan blades causes damage behind the fan in the outer casing and not to fan blades

nnc0

The individual blade doesn't flex forward, the entire fan assembly displaces forward under a thrust load. You can get a sense of how much just by looking at the wear plate. Or look at an enlarged dwg of the fan assy in cross section

ulisse

ok thanks for the info

but at the end wath if I do have high reading on eng vib values during the run up (5 or 6 n1 vib)
shall I continue the flight or suspect big engine ice contamination and return to gate.

rudderrudderrat

Hi ulisse,
You should wait until the vibs have returned to normal (within ??? secs whatever your manual says). As soon as the vibs are normal, you may assume the ice has been shed so can commence the take off.

We wouldn't take off if the the vibs were still abnormally high after 60 secs (RB211-22B time limit).

ulisse

ciao
I was not able to find such a description on the fcom

some one could give some reference about that

rudderrudderrat

ciao ulisse,

Refer to FCOM/SOP-09-AFTER START-Engine Anti Ice.
A320 says "accelerate engines to approx 70% for 30 secs.
....should be performed just prior takeoff with particular attention to engine parameters to ensure normal engine operation."

If you haven't got normal VIBs etc after 30 secs then go back to stand.