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boofhead
18th Feb 2008, 20:29
I don't remember seeing anything official about takeoffs with the ice on the wings polished instead of removed. It is done though, in some conditions it is the only way to do it since some temps prevent removal of the ice completely (using hot water gets the ice off but it freezes in turn and all you can get is a smooth surface, with a small layer of ice remaining).
If the ice is light rime or frost it is easier to rub it smooth than to scrape it off or wash it off with hot water and it seems to work, but is that covered in any country's rules?

mustangsally
18th Feb 2008, 20:44
Danger Will Roger, Danger!

Never but never fly any airplane with any kind of ice on any flying surface, PERIOD!

I do know that it sometimes maybe done, but risk is on the wing. It is not worth it, take a couple of hours off, maybe the day or the week. But, before you wing it again have a clean, ice and snow free aircraft.

Ice is heavy, not to mention airflow problems, just don't do it.

Way to many demonstration of dumb aviatiors, learn from your fellow aviatiors mistakes and not from your own crash.

The Air Florida out of Washingtion DC is a prime example and that aircraft got deiced, but should have gone back for another.

Live long and go to the bar instead.

G-ALAN
18th Feb 2008, 21:48
What mustang sally said!

boofhead, just out of interest mate, where did you hear that ice can be polished? I had it hammered home to me from day 1 never ever to fly with ice on the wings, too many accidents have demonstrated why.

matt_hooks
18th Feb 2008, 22:01
A little in the way of explanation is called for I guess.

Ice on any lift-generating surface is a BAD thing. The reasons are manifold, but the main two are the addition of weight, and the change of the aerofoil shape. Even a fairly thin layer of ice can cause quite substantial changes in the lifting ability of an aerofoil section, and most often this will be in the form of a reduction in available lift. Add to that the extra weight of ice and you are looking at a dangerous situation, especially when attempting a take-off close to MTOW.

Additinally, if the ice accretion on each wing, or even along the length of one wing, is uneven then you can end up with a seriously off balance aircraft.

The problem with ice usually has very little to do with form drag due to an uneven surface, and everything to do with parasite drag caused by an inefficient aerofoil shape.

It's rather simple really. I wouldn't attempt to fly an aircraft with any ice on any surface.

As for using hot water to de-ice, that's not a good idea. If you've ever seen the effect on an iced up car windscreen of pouring hot water on you'll understand the problem. Differential expansion of the heated side can cause huge internal tensions to be created. The effect on glass in such a situation is often that the forces become too great and it cracks or shatters. Now the same effect can happen with aircraft skins, granted to a lesser degree due to the better thermal conductivity of the metals, but it happens nonetheless. Aircraft de-icing on the ground is carried out using a de-icing fluid, which consists of a chemical that causes the freezing point of the water to drop, thus preventing re-icing. Even then there is a limited "hold-over" time before a re-application is necessary.

MarkerInbound
18th Feb 2008, 22:02
(using hot water gets the ice off but it freezes in turn and all you can get is a smooth surface, with a small layer of ice remaining)

There's a reason you use de-icing fluid. The freezing point has to be below ambient.

yrvld
18th Feb 2008, 22:05
Air Florida crashed mainly because they did not use the engine anti-ice, therefore getting erroneous thrust readings and less thrust than commanded, not because they did not deice or because they should have gone back to do it again.
About polishing the ice.. i heard a lot of crazy things, this sure stands as a good one. you sure it's not a joke?

Mad (Flt) Scientist
19th Feb 2008, 01:06
Frost polishing is actually referred to in a (IMO stupid) FAA document. The AAIB report on the Challenger 604 crash at Birmingham England a few years ago made specific (and, IIRC, scathing) reference to the FAA document in question...should be easy enough to track down....

Ah, here it is ....

AAIB Report (http://www.aaib.gov.uk/cms_resources/5-2004%20N90AG.pdf)

for example:

1.18.5.1 US Federal Aviation Administration Regulations

The following US Federal Aviation Regulations (FARs) dealing with icing of aircraft on the ground were relevant:

FAR Part 91.527: “No pilot may takeoff an airplane that has:···· (2) Snow or ice adhering to the wings or stabilizing or control surfaces; or (3) Any frost adhering to the wings or stabilizing or control surfaces, unless that frost has been polished to make it smooth.”
(my emphasis)

During the investigation, attempts were made to determine the definition of ‘Polished Frost’ and indeed how to polish frost. Nothing was found and the conclusion was that the explanation could have been lost in aviation history.

However, when considering why the crew of N90AG did not de-ice the aircraft, despite evidence that there was frost on the leading edge of the wing, the anomaly of ‘Polished Frost’ may be a factor. The existence of such a concept in both FAA and company documents gives an indication that some form of frost is acceptable and this may have influenced the attitude of this crew.

Enquiries were made of other national organisations to establish if the concept of ‘Polished Frost’ was widespread; neither UK nor Canadian Authorities recognise the concept. It is considered that the concept of ‘Polished Frost’ is particularly inappropriate and potentially dangerous to modern aircraft types and detracts from the importance of strictly observing the clean wing principle.

Accordingly, it has been recommended that the US Federal Aviation Administration, and all Authorities who follow FAA practice, delete all reference to ‘Polished Frost’ within their regulations and ensure that the term is expunged from Operations Manuals. (Safety Recommendation 2003-54).

Again, my emphasis.

Mad (Flt) Scientist
19th Feb 2008, 01:23
matt hooks
The problem with ice usually has very little to do with form drag due to an uneven surface, and everything to do with parasite drag caused by an inefficient aerofoil shape.

I'm not sure I'd agree with that. Ice's main effect comes through roughness rather than the shape changes - even the rather extreme double horn shapes used in certification don't do as much damage as you'd expect, but a layer of roughness - similar to sandpaper on the wing - can be horrendous on the leading edge. Because it's very much scale dependent larger aircraft can to some extent get away with roughness (though they shouldn't, of course, try on that basis) but smaller aerofoils can be seriously affected.

The effect is not just in drag but in significant changes to the stall behaviour in some cases, which can in the extreme turn a relatively docile, certifiable aircraft into an uncontrollable beast at much lower angles of attack (and hence higher speeds) than you may expect. This is really a flow breakdown mechanism - it's as if some evil genie snuck up and glued a bunch of random stall strips on your leading edge, in effect. Not something you want to find out about at 50ft AGL or thereabouts ....

galaxy flyer
19th Feb 2008, 08:12
Well said, MfS. I refer you to the thread on the Yerevan CRJ accident on R&N. The old wives tales on ice coated wings could a fill a very dangerous book. I especially like the "lots of speed before rotation" and "full thrust will power us out" ideas. The old bags should be put to death.

GF

I just checked and that silly regulation is STILL there! It's a wonder anyone listens to the FAA. Oh, they don't? Good.

matt_hooks
19th Feb 2008, 14:10
Agreed MFS, surface roughness is a big problem with ice. And yes, the mechanism is as flow separation. Hence many hypersonic missiles have, counterintuitively, a roughened nose surface. This means that the air flow separates and becomes turbulent close to the nose of the missile meaning, again counterintuitively, less drag-production by the rest of the body.

I would still suggest that any significant ice accretion is likely to have the effect of changing, adversely, the lift producing characteristics of an aerofoil section. And the big problem is that this is entierly unpredictable, leading to flight with an unknown envelope which can readily lead to problems.

And yrvld, I seem to remember something to do with reverse thrust being used on the ground to back out of the gate, causing ingestion of large amounts of slush and ice into the engines. This exacerbated by the omission of engine anit-icing use. Of course, to try and isolate one cause is stupid and counterproductive, but it's a very interesting example of the holes lining up!

bookworm
19th Feb 2008, 17:02
The AAIB report on the Challenger 604 crash at Birmingham England a few years ago made specific (and, IIRC, scathing) reference to the FAA document in question...should be easy enough to track down....

Strangely enough, I recently found and quoted the same passage on a different forum. I think the CVR captured an exchange that sums it up nicely:

Commander: “GOT A (????) FROST ON THE LEADING EDGE, ON THERE, DID YOU-ALL LOOK AT IT?”
Handling pilot: “HUH?”
Commander: “D’YOU (????) THAT FROST ON THE LEADING EDGE – WINGS?”
Handling pilot: “ DID I FEEL ‘EM?”
Commander: “YEAH, DID YOU-ALL CHECK THAT OUT?”
Handling pilot: “YUH”

They lived for a further 14 minutes.

Pugilistic Animus
19th Feb 2008, 19:44
Polish The Ice,= :mad: Th pooch

boofhead
21st Feb 2008, 16:46
Thanks for the reference. A bit hard to counter it if the FAA approves the procedure.
It is not always possible to find deice fluids, and there is a push to restrict the use of most fluids due to the contamination they cause to the local environment. Hot water works, and that is a major part of Type 1 fluid, which is approved for light airplanes. Hot water and a couple of towels will get the airframe clean, although it takes a bit of time. Wing covers would be the best option.
I put my little airplane ( a biplane with plastic wings) in the hangar to thaw it out, was left with water on the wings which was pooled in big drops because I had (stupidly) polished the wings thinking that would help remove any ice (it did not, made it stick harder). I figured the water would blow off on takeoff.
The OAT was just below freezing.
After takeoff the airplane flew real squirrelly, lost all its stability, in pitch and yaw. Made me sit up straight! Had to be real careful, although lift off speeds were fine and also high speeds. Only the mid range speeds were affected. Landing was normal.
After shutdown I found that the water droplets had all frozen in place when the lower pressure due to lift being generated caused the temp to drop so fast the water instantly turned to ice. They were like Hersheys Kisses in shape, all over the wing and tail. So hard and sharp that if I had run my bare hand across them I would have gotten my palm cut. I was amazed that the airplane even flew.
I cleaned it all off to return to home base, the temps had remained low all day. I was left with frost, and could not get it all off, no matter what. As I cleaned one part, previously cleaned areas would frost over. There was mist in the area and although it was not being called, I think it was approaching freezing fog conditions. I got it all off except a few areas that I figured I could do without and polished them smooth.
The airplane flew pretty well, only a tendency to yaw instability (and this airplane has such a problem even when completely clean). It is an amphib and often flies with water on the wings, I normally do not experience any extra problems when operating on water, but I guess the water does blow off under those conditions.
Anyway, it is an interesting subject.

Grunf
22nd Feb 2008, 00:26
Woman, Child Lost In Maine C-525 Downing


Pilot Reported Instrument Problems After Takeoff

A successful businesswoman and her son were the victims of the Friday night downing of a Cessna 525 CitationJet near Augusta, ME.



Jeanette Symons and her 10-year-old, Balan, were the only persons onboard the Citation, which took off from Augusta State Airport (AUG) at 1745 local time Friday, bound for Lincoln, NE. Symons, the founder and CEO of the youth-oriented social networking website Industrious Kid, was the owner and pilot of the aircraft, reports the Augusta Sun Journal. The plane's registry was N102PT.



Flying under an IFR flight plan, Symons made radio contact with departure control at Portland International Jetport after takeoff. Soon thereafter, with the jet at about 3,000 feet, she declared an emergency due to apparent instrument failure. The paper says the pilot reported a problem with the aircraft's altitude indicator.



FAA spokesman Jim Peters said the controller attempted to vector the Citation (type shown below, right) back to Augusta, but lost contact with the jet and then saw it descend rapidly on radar. The plane impacted terrain roughly 10 miles from AUG, leaving a debris field about 300 yards long.



Weather conditions at the time of the accident were less than optimal, according to AUG airport manager John Guimond, with freezing rain from a passing storm blanketing the area. "Taking off in that may have been a bad idea," he said.



Tim Donovan, co-founder of Industrious Kid and a friend of Symon's, said Balan was the inspiration for the launch of the company's social networking site, Imbee.com. The site provides blogs and social posting for children, that can be monitored by parents.



"Her kids wanted to be online, but she wanted to be in control and that is where Industrious Kids came from," Donovan said.



Symons and her son reportedly arrived in Maine last weekend, for a week-long ski camp at Sugarloaf USA. Her eight-year-old daughter was at home in Steamboat Springs, CO, during the trip.

boofhead
22nd Feb 2008, 00:33
Happens too often.
At least I don't try to fly IMC! (haven't got any IFR instruments anyway).

Say again s l o w l y
22nd Feb 2008, 01:20
As has been mentioned, don't mess about with any ice of any kind.

Some figures I gleaned from those fairly intelligent people in research at NASA were that the weight of ice is minimal compared to it's other effects. For example using their Twotter test aircraft and wind tunnels, they found that drag increased by up to 40% and lift decreased by upto 30% when iced up.

Pretty significant figures. However, even more alarming was the movement of the centre of pressure and especially the effects on the tail of the aircraft. Approach speeds were all to cock obviously and the stalling characteristics became "interesting". The test pilots definition not mine. Mine would have been terrifying......

There is some good stuff out there to read up on, but the simple rule is the best. If iced up, have it removed fully and by the correct method. If you can't go back to the bar and fly another day.

speedrestriction
22nd Feb 2008, 09:29
Our AFM allows us to fly with a small depth of ice/frost on the underside of the wing. Anyone have any thoughts on this?

411A
22nd Feb 2008, 11:24
It would seem that we have some folks here who are, shall we say, new to aviation, and are not aware of past procedures on many older types.
While it is true that many new(er) types will not tolerate frost on the wings (polished or not), many older types (DC-3, as an example) can be flown quite safely with well-polished frost.
As for frost on the underside of wings on jet aircraft, B707's (again, as an example) had no restrictions whatsoever in this regard, so a few youngsters who, having never flown older types, will more than likely be unaware.

Say again s l o w l y
22nd Feb 2008, 11:48
The more critical wing shapes we use now are far less tolerant of ice than the barn doors of old. The accident statistics show that modern practices of de-icing and being incredibly cautious of any ice, is the correct one.

I'm sure you cn "get away with" an awful lot, but why take the risk and where do you draw the line?

Ice under the wing has a smaller effect on the aerodynamics than on the top surface and if your Op's manual says it's OK and you are happy, then off you go, but when there is ice underneath, there's ice on top, so if the top needs to be deiced anyway, why not get the whole lot done?

742
22nd Feb 2008, 21:01
Here is the FAA's view on their own polished frost regulation:

http://www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/safo/all_safos/media/2006/safo06014.pdf

Bottom line--they don't like it and it is going away.

punkalouver
23rd Feb 2008, 01:25
While it is true that many new(er) types will not tolerate frost on the wings (polished or not), many older types (DC-3, as an example) can be flown quite safely with well-polished frost.
As for frost on the underside of wings on jet aircraft, B707's (again, as an example) had no restrictions whatsoever in this regard, so a few youngsters who, having never flown older types, will more than likely be unaware.

What about the big......Aaaaah Lockheed?

411A
23rd Feb 2008, 01:35
What about the big......Aaaaah Lockheed?

The big Lockheed three-holer must be de-iced...however, frost on the underside of the wing (as you might find when the aircraft is landed in a humid climate after a long flight), no problem whatsoever.
None, zip, nada.

Speedbird48
23rd Feb 2008, 15:24
Here we go again getting back into history, and a modern generation that seem to have missed something on the way up.

The procedure was "To remove FROST from the surfaces" It did not say ICE. Various parts of the world are prone to heavy frost, and may not have freezing rain or large snowfalls.

On the older big pistons, DC-3, DC-4, DC-6 etc. and various English and other airplanes there was a procedure to remove "FROST" from the surfaces by passing a length of dry fire hose from front to back, or coarse rope, and with a see-saw motion it would polish the "FROST" off. Been there done that etc. back in the '50's and '60's.

Those old wing sections were nowhere near as critical as the new ones with rivits and bits sticking up or stuck on the top surface. Big propellers passing large amounts of air over those surfaces made for lift as well, not so today with your jets.

When you have a wing such as the CRJ that has a peformance penalty for any sealant that may be missing from behind the leading edge section where it is fixed to the wing, and no dents allowed in that leading edge section, or "bondo" repairs, you have a problem airfoil, otherwise known, and proven to be, critical.

We have come a long way with our knowledge, unfortualty as seems to be too frequent in this business at some great cost in lives and machines, but we do need to remember that we have not yet reached perfection although we are trying hard.

We have new rules, "if it has frost ice or snow on it, don't fly it".

The younger generation could do well to read some of the history that came with the experience that has got them where they are today, and they may then understand a bit better without the ridicule that seems so often to come in some Pprune threads. It is not all in school books and "on line". It is experience!!

Speedbird 48.

galaxy flyer
23rd Feb 2008, 23:15
Absolutely right, Speedbird 48.

Mad (Flt) Scientist
8th May 2008, 23:16
FAA NPRM (http://www.faa.gov/regulations_policies/rulemaking/recently_published/media/PolishedFrost.doc) now released to remove references to "polished frost".

SUMMARY:
The FAA is proposing to remove provisions in its regulations that allow for operations with “polished frost” (i.e., frost polished to make it smooth) on the wings of airplanes operated under parts 125, 135, and certain airplanes operated under part 91. The rule would increase safety by not allowing operations with polished frost, which the FAA has determined increases the risk of unsafe flight

galaxy flyer
9th May 2008, 04:08
Would "it is about time, FAA", be too harsh!!

GF

OutOfRunWay
9th May 2008, 08:20
Ice builds up on ice which is already there faster than on clean surfaces. If you polish frost, you may actually be able to fly, BUT there is now a layer of ice where the anti-icing can't get at it, and where ice can now build up when on a properly de-iced surface, it wouldn't.

Do your de-icing properly, and watch your holdover times! Accept no substitute.

OORW