Tail icing
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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....
Anyone know anything about certification etc....
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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.
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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!
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!
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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.
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.
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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.
Only half a speed-brake
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.
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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.
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...but clean wing strategy cannot be underestimated.
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.
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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.
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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.
As for tail icing, the trimmable tailplane seems to eliminate this as a problem.
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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.
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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.
PM
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.
PM
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.
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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
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
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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.
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.
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Mad (Flt) Scientist
What has eliminated tailplane icing as a safety hazard is not a specific design feature (such as trimmable tail)
What has eliminated tailplane icing as a safety hazard is not a specific design feature (such as trimmable tail)
Only half a speed-brake
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.
PM
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.
PM
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)
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411A -
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.
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.
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 !!!!!
Only half a speed-brake
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!