Aircraft Icing

[Capt Wannabee]

Wondering if someone could help.

I was talking to someone this weekend who flies piston twins. He was saying that if you get significant ice build up and can't maintain altitude (through weight increase or engine loss) that you find what the stall speed of the aircraft has increased to and then try to fly just above it.
After thinking about it later on I was wondering about the ice build up. Surely it will not be uniform across the aircraft and you will get a different build up on each wing. Therefore the wings will have different stall speeds. As you try to find the stall speed couldn't you then find yourself in a spin as one wing stalls before the other?
Does every company have the same procedure for severe icing?
If you were already low would you want to risk stalling the aircraft in an unknown condition?

Cheers

Edited to remove mistakes caused due to a heavy weekend!! Cheers for pointing that one out GT!



[This message has been edited by Capt Wannabee (edited 02 July 2001).]

[GT]

Hi Capt Wannnabee,

"...stall speed of the aircraft has reduced to...", surely 'increased to'?

Regards, GT.

[Genghis the Engineer]

The main hazard of icing is that the LE ice formation changes the aerodynamic properties of the wing. This will certainly reduce available climb rate, etc. as well as increasing stall speed. Other interesting affects, which will vary with aircraft type, include loss of AoA indication, tailplane stall, loss of pitch stability with flap selection, etc. etc.

If an aircraft is cleared for deliberate flight in icing, then there should be a section or supplement to the manual stating the correct handling techniques and quantifying the performance degredation. The correct answer is in there for a particular, but I can't see that sitting just above the stall, with potential for further icing and further increases in Vs is particularly clever.

G

[Genghis the Engineer]

Just another thing. "Finding what the stall speed..." generally means stalling the aeroplane. With ice all over the wings, probably, affecting handling, stalling characteristics, incipient spin, etc. etc. this could potentially prove your first and last sortie as a test pilot, or just your last sortie.

G

[Capt Wannabee]

That was my point. I thought it sounded pretty daft. My original post was asking if you do stall in the aircraft couldn't you end up in a spin due to the uneven ice build up, like you said its the last spin you will ever be in!
I was wondering what other companys do. The more I think about what this person told me the more crazy it sounds.

If you have heavy icing on an aircraft that is affecting your aircraft to the point that you are struggling to maintain altitude what do you do?
Stalling the aircraft to find the new stall speed and then trying to stay above it and maintain your new best glide speed dosen't sound too safe to me as won't that stall speed keep increasing anyway?
Do you just come belting down making sure you don't stall under any circumstances?

[Capt Wannabe]

Well, I was told today in no uncertain terms that this is a load of crap. I wouldn't quite have put it that way myself, but the much more annoying point is that I was accused of starting this topic.

[This message has been edited by Capt Wannabe (edited 03 July 2001).]

[Capt Wannabee]

Sorry for posting a load of crap. I was genuinely wondering about this, as I know nothing about aircraft icing and what to do should you encounter it. I was just going of what I was told by someone and wanted more info. Sorry for trying to find anything out!!

Sorry the original CW for causing you grief.

Posted by the impostor not the original! :)

[Genghis the Engineer]

Captain Wannabee,

This is the sort of conversation that aught to go on between aviators, professional or otherwise, if we're ever going to learn anything. The approach to dealing with icing may be poor, but your attitude in asking intelligent questions is correct. It also seemed perfectly clear to me that you didn't know, had heard some advice you were uncertain of, so were asking for more advice.

Anybody who is criticising you for asking intelligent questions about a safety related subject, probably has a point of view less valid than your own.

G

[Capt Wannabe]

Sorry if I was misunderstood, re-reading my post, I see I did not make myself clear.
I am of the opinion that there is no such thing as a stupid question if you do not know the answer.
My point was that somebody came to me personally and accused me of posting a load of crap, when in fact I had not even looked at PPRuNe for several days.
Genghis, I totally agree with you, but unfortunately this opinion is not shared by all professional aviators.

[Capt Wannabee]

GE and CW I am glad you understand and thanks for sticking up for me. I am a bit disappointed that someone actually came up to the original CW and told him the post is a load of crap.
Professional aviators probably don't want to read these kinds of posts - hence why I posted it in Wanabees and not in tech log or anywhere else.
I was unsure of something I had been told and would have liked to hear opinions on dealing with icing from more experienced wanabees or professionals who look on wanabees and therefore don't mind giving advice.
If someone came to me at work and asked me a question about something and they were totally wrong but were just repeating or going off what they had been told I would not say that is a 'load of crap'. As a professional I would be glad that they had the sense to go and ask someone for advice, as they were unsure. I would then (if I knew) tell them the correct way of doing things as everyone needs to learn and you only learn by asking.
To all the professional aviators (particularly those who had a go at the original) who were annoyed by my crap posting I apologise and assure you that I shall refrain from posting anything in the future that asks for advice on something I am unsure about.

Sorry for the outburst but most of us on here are here to learn, pick up tips and ask advice, probably why it’s called wanabees not professional experienced aviators forum!!

P.S If anyone can tell me what to do in extreme icing I would really appreciate it or am I taking the piss now!! :rolleyes:


[This message has been edited by Capt Wannabee (edited 04 July 2001).]

[Chuffbaby]

The standard procedure in heavy icing is to leave the FL that is causing the problem. If that leaves you below safety altitude or above your performance ceiling then you have left it a bit late - declare an emergency and get radar vectoring towards your nearest suitable airfield.

Prevention is a lot better than cure - most aircraft considered fit for flight into known icing conditions will have a weather radar fitted - this will be used to avoid areas where severe icing is likely.

------------------
You know when you've been CHF'd!

[Zeke]

CW

This is not a silly topic, it has caused many deaths, the problem is not only associated with smaller pitson aircraft.

A number of inidents come to mind that were a result of icing, I understand that ATR have had a number of stall spin fatal accidents in the states.

As a result of this they test flew some ATRs behind a modified C130 that would spray water to aircraft to build up ice to see the effect of it on the aircraft. I understand they improved the de-ice capabilities of the aircarft after this.

The MU-2 also had a nasty habbit of icing up it underside whilst on night freight. The autopilot would keep trimming back to maintain altitude until it reached it limit, disconnect and kill the pilot. The MU-2 does not have ailerons, it used spoilers for lateral control.

I think the Australian ATSB is about to release today (announced on the SAAB web site) a report of an investigation into a SAAB 340 that was holding near Melbourne, whilst in the holding pattern ice built up, it went into an inverted spin, the guys got the aircraft out (just) and landed ....nice work.

Aircraft certified for flight into icing conditions normally have a big notice in the flight manual, not certified for flight into severe icing conditions. On turboprops its normally goverened by ice build up on the spinner, windscreen, of ice build up in exceess of the cycle of the de-ice boots.

Z

PS would the real CW put his/her hand up :)

[Pilot Pete]

CW

I think you will find that you are right to question what you'd heard. Flying in icing conditions is a serious matter and I think you specifically mentioned this in relation to piston twins. I have considerable experience of flying pistons for Public Transport purposes up and down the UK and into Northern Europe.

The first thing to consider is the equipment fit of the a/c. Is is equipped for icing conditions (boots, prop heat etc etc). If it is not then the simple answer is;

1. Don't go into icing conditions
2. If you find yourself in icing conditions get back out of them. (Consider 180 turn, descent below zero degree isotherm, diversion etc etc)

If the a/c is equipped for icing conditions then you may fly in icing up to (or should that be down to?) the 'stated' categorisation (ie equipped for 'moderate' icing). Simply, this means that if the de-ice/anti-ice equipment is managing the ice build up sufficiently then you are ok. If it is not you must follow the steps pointed out above for getting out of the problem; that's a command/experience decision. Your original question was about the 'procedures' a piston twin pilot should follow.

In the company where I worked flying C310,402 & 404's the procedures were pretty similar accross the whole fleet (all piston/unpressurised)and they were, upon entering icing conditions;

1. Prop heat on
2. Power and prop levers up to the 'top of the green' band
3. Operate the boots as soon as a build up of ice occurs on the leading edges (there used to be an idea of leaving the build up to 1/2-3/4 of an inch, but this theory has been superceded)
4. Monitor the situation and consider what options are available should the situation worsen.

From the above points, the first is self explainitory, but the second requires a bit more detail. Pushing the levers forward to the 'max continuous' settings does a number of things;

1. Increases prop RPM's and helps to 'fling' the ice off the props.
2. Increases TAS and lowers the nose slightly thus presenting less of the 'underside' to the icing. This was imperative on the C402 & C404 which were extremely prone to getting heavier as the ice built up, leading to the autopilot trimming the nose up to maintain the altitude, causing the speed to decay and presenting more of the underside to the relative airflow/icing leading to more build up of ice on areas that are not equipped with de-ice/ anti-ice and thus the situation getting worse and worse VERY QUICKLY.
3. The increased airspeed keeps you further away from the stall speed, which as stated will be incresing with ice build up.

So, what you heard is indeed VERY DANGEROUS in any aircraft; flying around at just above the stall is not something you want to be doing in crap weather conditions, think about what is going on in point 2 above and you can see that it is a sure recipe for disaster.

Also remember that flying piston twins generally means that you will be flying around 'in' the weather (especially if unpressurised - below FL100) so you are more likely to be exposed to icing and quite often you are being bounced and battered around at the same time.......it's not for the feint hearted, and contrary to what someone else said, piston twins do not generally have Airborne Wx Radar fitted. Some of our fleet did but they were the exception. It needs to be stressed that it comes more down to a command decision process rather than just a procedure. Keep your options open and really look at those wx charts and zero degree level in relation to MSA's before you go and look for the areas that might cause problems and think about enroute diversion airfields etc etc.

Otherwise it was always jolly fun half way accross the North Sea in the middle of the night in imbedded CB's with no wx radar and hail pounding the screen with your seat belt strapped as tight as you can get it and just a piece of urgent freight to keep you company!

Safe flying

PP

[Capt Wannabee]

Thanks for taking the time to reply. It was very informative.

[Tinstaafl]

At night, without Wx Rad. or a stormscope you really appreciate whoever thought up those intermittently, internally illuminated clouds so you can find the TS! :)

[Zeke]

Tinstaafl

An ADF will point to TS, they are a poor mans stormscope

Z

[ 07 July 2001: Message edited by: Zeke ]