engine lip ice in flight - Page 3

Yariv · 07-26-2008, 11:34 AM

the airfoil shaped portrusion is called a strut, and it houses a magnet that creates the vibration. it has no aerodynamic function, nor is ice detected on the strut. airflow over the strut or over the probe is irrelevant. ice is detected on the probe, which extends 1 inch from the strut. there is no reduction of ambient temp. the reduction of the compressibility effect (due to being about 1.5 inches away from the fuselage) is negligible and certainly not close to 10*c.

which is why the cfm on other airplanes with nearly identical detectors (though not all airplanes... but on the one I'm flying now) says that you do have to manually turn on engine a/i. Ice will not build up on the detectors when TAT is >0*c, but it will theoretically build up in the intake when TAT<=10*c.

carry on...

kidicarus5897 · 07-26-2008, 12:51 PM

All right, new procedure- everyone has to turn on the ENG LIP A/I in flight if the TAT is 10 degrees or less or you are willfully putting all lives on the aircraft in danger. Obviously the engineers don't know what they are doing and it is just luck that we have all diverted disaster up till now! Good god, I feel like I have let everyone down!

lonestarwings · 07-26-2008, 01:40 PM

Quote:

Originally Posted by Yariv

the airfoil shaped portrusion is called a strut, and it houses a magnet that creates the vibration. it has no aerodynamic function, nor is ice detected on the strut. airflow over the strut or over the probe is irrelevant. ice is detected on the probe, which extends 1 inch from the strut. there is no reduction of ambient temp. the reduction of the compressibility effect (due to being about 1.5 inches away from the fuselage) is negligible and certainly not close to 10*c.

which is why the cfm on other airplanes with nearly identical detectors (though not all airplanes... but on the one I'm flying now) says that you do have to manually turn on engine a/i. Ice will not build up on the detectors when TAT is >0*c, but it will theoretically build up in the intake when TAT<=10*c.

carry on...

I believe you, but what's the point of giving the "strut" an airfoil shape if it isn't designed to simulate conditions on the wing/engine lip?

I realize that little nipple is what's vibrating, but how far into the strut does it go? If part of that nipple extends into the strut, couldn't ice accretion on the airfoil shaped strut affect the nipple's vibration enough to turn on the anti-ice?

CFM 2-15-15 page 1 Code 02

"The ice detector was designed to pick up ice quickly. Therefore in most cases, ice will be detected before it can be noticed by the crew."

To me this means the ice detector will pick up ice before the engines are affected by ice accretion. I'm sure we've all had plenty of flights when there hasn't been a trace of ice on the nose or windshield yet the automatic anti-ice system is triggered. It doesn't take much (.020 inch) for the A/I system to be activated automatically.

Don't get me wrong, I respect your right to follow the manual technique, I'm just presenting the argument why letting the automatic system take care of it is probably OK (otherwise I'd imagine we would have seen your technique referenced in CFM vol. 1 by now). I also don't know much about how that ice detector is constructed, just attempting to justify my own technique and the technique of the other 150 or so captains I flew with before I upgraded.

Yariv · 07-26-2008, 04:20 PM

all right, I'm being a hard as$, that seems to be my self appointed job here.

I'm not trying to change the book or change what you do. just forcing you to think a little. just because the book doesn't require it doesn't mean it's safe not to do it. just because there hasn't been an incident doesn't mean we haven't come close or won't have one eventually.

the simple fact is that ice can build in the nacelle while the ice detectors are not detecting ice. lonestar gave it a good try, much better than saying 'but the book doesn't require it' or 'but nothing bad happened so far'. unfortunately the mx manual explains that only the probe is vibrating, and the strut is fixed. I'm not sure why it's airfoil shaped, other than to say 'what shape would you make it?' it is NOT supposed to simulate pressure drop thru the nacelle, to the best of my knowledge and research. the ice detectors detect ice when it is building on the airframe, i.e. visible moisture, temp below freezing (TAT).

how much time do you spend flying with TAT between 1 and 10*c and moisture present? not much. so this is not a big deal and the chance of an incident is small. airplanes without ice detectors (and some that do have them) have a requirement to turn engine a/i at <=10*c w/ vis moisture. our ice detectors DO NOT detect ice above 0*c. so why aren't we turning engine a/i on between 0-10? that's all I ask. "because it doesn't so say in the book" isn't good enough, although it does get you off the hook.

fly safe!

kidicarus5897 · 07-27-2008, 02:11 AM

Quote:

Originally Posted by Yariv

so why aren't we turning engine a/i on between 0-10? that's all I ask. "because it doesn't so say in the book" isn't good enough, although it does get you off the hook.

fly safe!

Hey man, that was my origional question.............get your own

lonestarwings · 07-27-2008, 02:50 AM

Good discussion, and I can definitely see why it'd be good to cover your bases by turning it on manually with tat < 10* and vis. moisture.

Yariv · 07-27-2008, 12:47 PM

Quote:

Originally Posted by kidicarus5897

Hey man, that was my origional question.............get your own

yes, it was yours! well done.

excuseme · 07-27-2008, 02:27 PM

Quote:

Originally Posted by Yariv

767 has automatic ice detectors very similar to the EMB. CFM sepecifically says, however, to turn engine ice protection on with visibile moisture and temp betweeen 10 and -40. so having an auto system means nothing.

Minor correction - SOME B767 are automatic. Some are not. As far as even thinking of questioning your EMB-145 systems knowledge... probably not

D-Luv · 07-27-2008, 03:37 PM

It's funny because we do this on T/O if it's <10 and moisture is present. But that's the only time.

Yariv · 07-27-2008, 09:32 PM

Quote:

Originally Posted by D-Luv

It's funny because we do this on T/O if it's <10 and moisture is present. But that's the only time.

lonestar tried to explain that by having airflow over the sensor at other times. airflow doesn't affect the sensor's ability to build up ice, and there is no temp reduction on the sensor probe itself. so your question is valid - why on t/o but not later?

excuseme, excuse me! I stand corrected. but the 762 and 764 that I fly (or at least qualified to fly... too junior to actually see them ) have detectors and cfm still says to manually turn eng a/i on if it didn't come on and it's <=10* w/vis moist.