Tail icing
 

Anyone got an opinion on why horizontal stab leading edges are not heated? Not on B737-200 and narrow body Airbus anyway. Had to get sprayed the other day for a very thin coating of ice on the stab leading edge. Nothing else anywhere and I thought it was a big waste of time/money. If the manufacturers aren't worried enoght to put in the plumbing.....
Anyone know anything about certification etc....

They are heated/protected on both the MD-80 Series and the DHC-8, and maybe almost every T-tail?

Anitice and deicing are two different things, T-tails generally had anti-iceing as well as some older jets. Guess it may be that lower airfoil tails do not ice in flight, possibly from jet exaust or probably design.

It a straight compromise. Big fin and tail that will still offer control when iced up or small surfaces with anti-ice system.

If it's a long way from the source of hot air to the surfaces it might be worth having bigger surfaces and no pipes. If the engines are right next to the surfaces it might be better to have smaller surfaces which are anti-iced.

If your stall characteristics are a bit iffy you might need both!

Tail surface anti-icing is absent from a lot of jet airplanes.
The L1011 is but one example.
Even the B707...it came from the factory with tail surface anti-icing installed, but it was disconnected by many 707 operators, with regulatory authority approval.

The primary reason that tail anti-icing is missing from many large jets (and some smaller ones) is that during certification flight testing, either with flights behind a spray aircraft, or with various shapped blocks glued to the tail surfaces, no adverse flight difficulties were found.

Thanks. I actually heard that Boeing secured 4x4 timbers to the stab leading edge of the 737 during certification to demonstrate that protection wasn't needed! We are so over the top in Canada about de-icing that even a skim left over from the last approach (nothing on the wing leading edge because WAI was on) must be removed! Ridiculous and expensive.

No. You are clearly out of place. Back to ground school reading about Dryden and Potomac accidents. The lessons learned together with exposure and expertise available from Canadian CAA helps other international operators stay safe.

Yes, it is costly and sometimes just "pro forma", but clean wing strategy cannot be underestimated. Once you treat your self to carry out ops outisde approved regs, you need to ask but one question: If good girls do go down to the floor, just how low will the bad girls go? Making one look smart for avoidng (euphesiasm) regulatory limits, brings consequences with spilled blood and twisted metal. Unlike lawyers and investment bankers, no pilot is payed enough to benefit from intentionally avoiding best practice procedures.

Once had a B757 arrive that had been crew training all day around Bedford (Thurleigh) in low cloud icing conditions, and both horizontal and vertical stab leading edges had approximately 6" thick ice extending the complete span and wrapping itself around the complete L/E section. I questioned the crew as to whether they had experienced any handling problems to which they replied no, once they saw the ice for themselves they were as surprised as i was. Still it was a good indicator of what little difference ice on the tailplane L/E's makes.

Are you sure you are correct? Firstly, we are talking about tail surfaces, secondly we are hearing that aircraft are appearing to be flying quite nicely when contaminated and lastly, nobody, absolutely nobody is suggesting that we shouldn't de-ice in the way that we are instructed. What is being discussed is "does the tailplane need to be de-iced?" and "if not why not?" and the fact that some of us have flown aircraft that have been contaminated in flight without the aircraft exhibiting any unpleasant flying characteristics.

Personally, I have been bitten (but not too badly) by a contaminated aerofoil. But to say that "ice will always kill" is patently wrong. All of us would be better off if we understood why some aerofoils were susceptible to suffering from ice and others were not. Until we have more knowledge though, we'll continue to piss away our company's cash being de-iced.

Leading edge devices
 

Has anybody ever heard of an icing accident involving an airplane with leading edge flaps/slats etc? All the t/o icing problems I recall are with hard L/E... short 9, F-28, etc. Seems like leading edge devices greatly reduce or eliminate the icing problem. Disregard the SAS MD & the DCA 737. Both of them flew, but failed to maintain flight due to lack of thrust.

BobM2: In the early `80`s the B737-200 had a series of well publicised significant wing drops after take-off which were I think attributed to assymetric leading edge ice contamination caused by the practice of crews using the reverses to control speed on taxying out. IIRC this resulted in a Boeing bulletin about early climbout pitch attitude.

Yes I remember that bulletin & I have experienced it myself on a 200 basic. As I recall it wasn't a problem on the 200 advanced. Back then, it was a much looser deicing culture--no type 2, no specified hold-over times, wing anti-ice inop on the ground. You deiced at the gate, then sat 30 minutes in the lineup with precip falling & then you departed. Can't recall any accidents though--except on hard wing aircraft.

As for tail icing, the trimmable tailplane seems to eliminate this as a problem.

What has eliminated tailplane icing as a safety hazard is not a specific design feature (such as trimmable tail) but rather industry acknowledgment of the risk, and designing for it, and having to certify for it.

As mentioned somewhere higher up, many types do not have tailplane anti-ice or de-ice, but have had to demonstrate, during certification, freedom from hazardous characteristics with significant ice accumulation on the tail - up to 3" of ice is the norm for most requirements. If your design can't hack it with three inches of ice, then you aren't going to get certified today, so your only choice then becomes to add something to prevent that ice forming.

Yes, the tailplane needs to be de-iced, and indeed anti-iced if necessary. It is defined as a "critical surface" for every type in existence, so it's a binding, regulatory, requirement that the tailplane, as for the wing and everything else declared "critical", be clean for takeoff.

Don't assume that because you have successfully flown an aircraft which has iced up, on an aircraft with no tailplane de-icing, that this means that tailplane contamination is not a concern for takeoff.

During certification, safe flight and acceptable handling is demonstrated for ice on the tailplane, as I mentioned above. The same is in fact shown for ice on ALL the unprotected surface, and even for failure cases for the protected areas. BUT there is one major exception - all of these demonstrations are conducted on an aircraft which is ALREADY AIRBORNE. There are no certification tests undertaken to demonstrate that you can safely takeoff - and in fact when we do the takeoffs with artifical ice to do the in-flight tests, we go to great lengths to mitigate the takeoff risks, which are considerable.

Yes, we do get airborne. But not at limiting speeds, weights or cgs. We make damned sure we don't overrotate, or rotate early. We do all kinds of things to try to make that takeoff safe. We certainly don't do things like mistrim the aircraft - something we DO do for the normal takeoff cert.

In short, takeoff certification, and thus the safety of the takeoff, is predicated on the CLEAN AIRCRAFT CONCEPT - and if you don't get the aircraft into the condition that was assumed for certification, you just became a test pilot, because you're pushing the envelope.

Next time you deice, ask the deicerguy if he actually deices the lower surface of the stabilizer.
I did one time, and the reply was that they didn't even have the equipment to do underwing deicing.
Now what does a stabilizer do, and what would be dangerous if it didn't?
The thing is there to produce a downdraft. It works like a wing inverted. The important surface is the LOWER one, and noone on this earth even bothers to spray it. Everytime we get deiced; i kind of smile to myself.
Deicers, where I work, are able to call for more deicing, and I as the Captain may not turn it down. In turn I would only be allowed to ask for more deicing than suggested by the deicer.
So everyday thousands of tails get deiced, without the people responsible even knowing what it is there for, aerodynamically.

The CRJ I fly has a Ttail, and it has no iceprotection built in. I have flown it in ice as bad as it gets and never even felt the difference to it being clean. I still get the ice sprayed off the leading edges (and the upper surface of the sabilizer) as I do believe in a clean wing. If only it was done right...

Nic

There have been a handful of events involving 727 and 737 aircraft experiencing buffet after liftoff, and the 737 has had its history of pitch ups. There have been a couple of cases in which the 737 was unable to rotate, but inadequate deicing was not proven to be the case, only suggested. The compressor stall/FOD problem is huge; I have tracked quite a number of those, and the safety ramifications are clear when one considers the SAS accident.

A common occurrence in the data is to fail to deice the upper surfaces of the horizontal stabilizer, particularly on T-tailed designs such as the Dash 8 and ATR. This results in excessive pitch up tendencies, often using all of the trim as well as forward control displacement. Typically, the deice crew failed to adequately cover the tail, and the flight crew cannot see it under any circumstances.

It is true that all icing is not fatal; that is precisely the problem. Icing is highly variable in effect, and it is quite easy for a pilot to misinterpret his/her experience. Current research is being done, and has been done for several years now, on identifying critical parameters of ice shapes so that worst-case models can be built. We already know that a few thousandths of an inch of surface roughness can seriously outdo the large ice shape, so bolting two-by-fours to the wing probably doesn't tell us as much as we used to think. Some parameters under analysis are chord location of the horn, horn height and horn angle. It turns out that horn angle can have quite an effect, and I'd be willing to bet that regardless of your experience or eagle eyes, you can't see a few degrees difference between one ice horn and another. Neither can the icing tunnel engineers, which is why the measured data is what identifies the worst case parameters, as opposed to ten years experience working in the tunnel.

The upshot is that, like a lot of things in aviation, this is a matter of margins. Some guys end up using up all the margin and go off a cliff, which is reported in the papers the next day for all to see. A whole lot of guys operate with vastly reduced margins and never know it. Protecting the margins is what safety is all about, because you will never see the one coming that gets you.

Of course, to do that professionally, someone has to take the time to educate pilots on where the margins are and how they are constructed, so that he can make decisions specifically aimed at margin protection as opposed to single event avoidance. That is where the industry training is woefully inadequate. Lately we have seen ample evidence of this in landings which depart the end of the rather short runway, but the same principle is active in many, many icing events.

Is there a non-trimmable tailplane certified without ice protection?

Agree 100%. My thoughts not corrected, but better explained.

If regulatory guidance say "ice will always kill" and under clean critical surfaces concept stab is deiced always for petite leading edge contamination we need to stick to rules. "No cutting corners" is an important message with broader impact that needs to be repeated again and again.

However technical questions are open for free discussion. Same as you, I had seen 2 inches of bullhorn ice on THS LE post landing, which is certified for OEI GA, while 1 mm of hoarfrost is illegitimate for tkof. Let's go figure.

BTW: My employer together with Virgin Atlantic (hearsay) is pushing Airbus to allow some upper wing frost (cold soaked fuel), similar to what 737NG is allowed to. So there is a light at the end of a tunnel after all. :)

Yours,
FD (the un-real)

With all due respect Sir, that's BS that was fed to you by Boeing probably. The 737 was 'certified' that way after Boeing 'showed' the FAA that with shapes on the tail.

I've related my experience with tail ice on the 737-200 on here before and let me tell you there IS an adverse control problem with tail ice. I also commented on the Midway accident regarding probable [my word] tail ice being the primary cause. I submitted my first-hand experience with tail ice to the Board with no luck.

Suffice it to say, if the wings will ice up, then so will the tail !!!!!

My training suggested that icing development is linked to leading edge radius, i.e. the sharpest airfoils will build up ice first. WRT B737 classics, I would agree that once wings start to ice up, the tail (thinner airfoil) is already contaminated!

All I can say is that after my experience with ice, I added ten to fifteen knots to the approach speed anytime wing de/anti-ice was needed on the 737s.

I could NEVER understand the Boeing idea. There they had this nice big heater right there in the tail [the APU] that they could've easily adapted, but chose not to to save a few bucks. Oh well................

Negative.
Lockheed actually glued five inch typically shapped ice formations on the horizontal stab...and found no problems, whatsoever.
As in none.
Info directly from the guys that did the flight testing, at Lockheed.;)
737?
Can't say, never flew that small jet.:hmm:

Large heavy jets are simply in another category, altogether.

Well, I consider "my" DC-8 a large heavy jet, and it was a real airplane with a heated horizontal stab. Any airplane that has an un-heated stab is not a real airplane. Naturally, IMHO.

The only section of the A380 wing that has Wing Anti-Ice is Slat #4 on each wing. ie. the middle slat of the three slats between the engines. (No Anti-Ice on the tail)

Indeed it is...any problems with tail icing?
The B707, which is just as large/heavy...had none.
Even with the tail anti-icing deactivated, which was the norm with many operators.

The May-June 1962 issue of Boeing's Airliner magazine details the deactivation and removal of the 707 stabilizer ice protection system. It is quite a classic read from an icing standpoint, reflecting a number of misconceptions about icing that have since been severely challenged, such as cloud vertical extent and droplet distributions, as well as the frequency of severe encounters. However, the key statement is that during testing with a representative three inch ice shape, no changes in control forces or stability were noted. This is the most important aspect, although they then devote a lot of verbiage to things like fuel consumption and landing climb weight limits due to limited thrust in some airplanes.

The only real threat from ice on the tailplane, and it is a big one, is tailplane stall during slightly higher speed approaches with full flaps. The early stages of this threat are manifested by changes in the control balance of the elevators, resulting in stick force lightening or outright reversal. This has a devastating effect on longitudinal stability, and quickly leads to elevator snatch, driving the control column full forward with the resulting pitch down.

This problem is neatly solved with irreversible (powered) flight controls, which are quite capable of overpowering a change in elevator balance. Thus, nearly all large jets have none of this issue, ice protection notwithstanding, because the elevator can easily be re-cambered to avoid the stall. The L-1011, of course, is a different animal due to the full flying tail, but I suspect that the aerodynamic analysis required to support the operation of that design in various flap configurations probably included huge margins to deal with ice contamination.

The 707, however, does not have powered elevators, nor does the DC-8 or DC-9 and MD-80. I know little about the DC-8 beyond noting that Douglas, apparently, opted to keep their tail ice protected when Boeing dropped it. That ought to raise a red flag; the Douglas fellows probably knew something that did not encourage them to press for a similar de-activation. I do know that the DC-9/MD-80 fleet has a problem with tailplane stall, and there have been a number of incipient cases with full flaps selected. Boeing, on the other hand, had enough stall margin designed into the 707 stabilizer to preclude any issues with the tested ice shape, and there is no service history that I am aware of in the zillion or so hours it has flown. Boeing has continued to design in that stall margin on subsequent stabilizer designs, while arguing insufferably against any certification requirement to do so.

No.....didn't worry about it with a heated stab.

If "your" de-activated 707 didn't have problems, maybe you were just lucky. Seems like even though Boeing built/sold more a/c, the DC-8 outlasted the 707.

And, as "Mansfield" said: "...the Douglas fellows probably knew something that did not encourage them to press for a similar de-activation."

OK.....I'm outta this discussion. You guys go fly your unheated tails but don't tell me that airfoils can't ice up under the right conditions and lead to fatal accidents like the Midway one. Most of us in/near that one ALL agree that tail ice brought that a/c down. In my write-up here on this Forum I mentioned the portion of the Accident Report that said that there wasn't any ice on the a/c because Charlie Fox Dog [Chicago Fire Department] said that when they got to the scene there wasn't any ice on the a/c. Well...DUH...the aircraft was ON FIRE !!

Good night.

Anyone in the know on the 787 being a bleedless aircraft, no anti-icing?

re 787
 

I believe it has some electric protection, on parts of the wing. I'd be astonished if they are bothering to protect tha tail

There seems to be a horrible confusion in some people's minds between "no effect due to icing" and "no icing on the surface".

I don't believe anyone at an OEM in any way inviolved in the design for flight into icing would ever say "flying surface X doesn't catch ice". If they did, they need to find a new job, because every flying surface on every aircraft ever made collects ice. It's the basic physics.

But I do believe that they could easily say "there is no (perceptible/significant) effect of icing on surface X". By which they mean "a pilot can't (easily) tell if there's ice on that surface" so we can, in most cases, just ignore it. I know I can happily make exactly that statement for many of our aircraft, with respect to ice on the tail; unless you're really paying attention to the trim required, you'll never spot the effect of ice on the tail. Because by design the tail is nowhere near stalling anyway, so a slight shift in the efficiency of the tail is all you see, which just shows up as a shift in the stab trim you use.

And yes, if you really work at it, you can even defeat that assertion - go fly in SLD, for example, and all the OEM's work for icing certification is valueless, and your only defence is to get the Hell out of the SLD, because we have virtually no idea what will happen - but we're pretty sure it'll be nasty.

I would agree. Clearly ice can accumulate anywhere, and if I think about how quickly ice can form on a flat, heated windscreen, then I dont want to think how fast it can collect on the tail of my 737. But surprisingly I've never seen large accumulations of ice on the tail after landing (after an approach in severe icing conditions), not much more than a light coat of rime ice on the leading edge without any noticable change in handling characteristics.

Something I recently read - Airbus chose to equip the mighty A380 with wing anti-ice, but actually the only part of the wing that is heated is the number four slat on each wing, nothing more. Is the airfoil designed in such a way that ice either has great difficulty in forming or that it can just take a lot of ice on the leading edge? Seems half-hearted to me, a bit like the 737-NG WAI where the outermost slat isn't anti-iced (just more extreme)....

You cant design an airfoil to not accumulate ice - if its stuck out in the breeze, it accumulates ice.

What that implies is that they have designed the wing so that ice on the rest of the slats/wing doesn't degrade the handling or performance enough that they need to antiice anything except the $4 slat. Usually there is a critical part of any wing - if you can protect the critical part, the rest can be left to fend for itself. The question is, how much do I have to preotect - it can be "all but a little bit", or it can be " just a little bit". Depends on the rest of the design.

I submitted a picture I took to our Safety Board for submission to the NTSB for use in the Midway accident investigation. It was a picture of our horizontal stab on a 737-200 that I took at the gate TWELVE [12] MINUTES after leaving icing conditions. There was FOUR INCHES of rime ice still on the leading edge of the stab. We took that into consideration during the approach and landed at VREF + a lot !!

Not nice to mess with Mother Nature !!

I'd think that it's a similar situation as with gust envelope protection --engineers and pilots do the best they can do based on data, statistical analysis and experience, while knowing that if She thus pleases; She can always shoot you...:\:uhoh:

B737NG?
 

Very interesting thread is this.

One comment puzzles me however.

My understanding is that even though Boeing consider it ok, the FAA (and every other NAA too) have insisted on the clean wing policy. I'm sure there's a directive somewhere.

Unless I'm just out of touch of course, again. :O

In a marked area on the upper wing is thin hoarfrost allowed, ice build up is very common there especially if the fuel is cold from the previous flight. We had serious problems in the beginning because the planes iced up in the canaries and it took up to 8 hours until the frost was completely gone, no deicing equipment there of course. Boeing OKed it and our local EU-authority is happy with that.

On the lower side of the wing icing up to 3mm is allowed as it was already on the classics.

As they should be, frost from cold fuel is common...it seems the new guys who haven't been around in airline flying very long have a fit about it.
Nothing new, either.:ugh:

Now, lets look at wing anti-icing on large (heavy) swept wing jet aircraft.
I flew the 707 in command for seven years, and did not once use wing anti-ice
No problems noted.
Now, after flying the L1011 for thirty years, used wing anti-ice perhaps half a dozen times...and only then because the airplane is equipped with an airframe ice detector, and the new First Officer bacame agitated and thought we would fall out of the sky, otherwise...gotta keep the co-pilot happy.:rolleyes:

I don't think any of us are questioning the way ice is formed (due to cold soaked fuel).

I was just trying to determine whether or not FAR121.629, with regard specifically to the B737NG had been revoked.

For those not familiar here it be....

I had seen this argument before, sounds honestly valid. Still, my understanding is that some NG operators are cleared for UWF within certified limits.


PS: Dunno about NG, but Airbus SA suffers UWF due to structural cold-soak on reinforced undercarriage rib. Indeed, tankering fuel won't help.

Turin,

I discussed this with the FAA yesterday...they do not allow any exception to 629. The 737 upper wing frost allowance was, apparently, based on an allowance by Transport Canada for West Jet (there may be other authorities involved, I'm not sure). The FAA was asked to look at it, but turned it down flatly because they cannot identify a reliable method for the evaluation of upper wing frost, i.e., 1/8 inch or 1/4, how can you tell by looking out the cabin window at night...

Frankly, I think they're spot on. A failure to detect upper wing ice during the preflight inspection is pretty common, particularly around the wing root area which is not visible from the cabin windows. I'm not sure how anyone can accurately assess a frost presence beyond determining that it is, or is not, present, and even that determination is not always reliable...