Wing anti-ice on the ground

[CaptainSandL]

Has anybody else heard that using thermal wing anti-ice on the ground after de-icing can invalidate the holdover time? Does anybody else use wing A/I after start in icing conditions either with or without a fluid de-icing?

S & L

[static]

We never use wing anti ice on ground (737).
On certain types it doesn`t even do anything on the ground, either disabled or simply not efective (e.g. 747).

I could imagine it "blows away" the protective glycol layer on the leading edge, just as a gale force wind would. This also shortens hold-over times.

[CaptainSquelch]

Glycol, not unlike other alcoholic beverages seems to evaporate when it get warm. That's why I hate "gluhwein"

Sq

[m&v]

Normally 'wing'heat is generally disallowed on the ground through the 'squat'switch to avoid o/heat/performance considerations.
The 320 can run a 30sec test if selected on the ground.Performance penalties apply on liftoff(bleed opens)

[Hew Jampton]

CAA Flt Ops has been asked time and time again why it is that one major UK B737 operator expressly requires wing a/ice on during taxi out in icing conditions, whereas another major UK B737 operator expressly forbids it. It's probably in their 'too difficult' tray (which presumably is bloody huge).

[Track]

Our Boeing (737) AOM states that WAI should always be ON on the ground if icing conditions exist. Only if deicing fluids types II and IV are used you can leave it off. I would think this is the same for every 737 operator or not?

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Track

[static]

Hi Track,
Since I operate in The Netherlands as well, also on 737`s I`m surprised. We never use WAI on the ground. On most of our 737`s it`s even inhibited. Air/ ground sensor prevents WAI valves from opening on the ground!
Weird eh?

[TopSwiss 737]

Our instructors teach us to switch on the Wing Anti-Ice together with Engine Anti-Ice on the after start scan, if in icing conditions... The WAI valve closes when thrustlevers are advanced beyond Take-Off Configuration Warning position, the switch trips off when weight comes off the main gear.

[static]

Topswiss,

Sounds the same as our 737-300`s.
The rest of `em only have a ground test possibility, this opens the WAI valves for 30 sec.

[Track]

Static, you fly for van Wijk I guess.

I must say I find such differences in use of WAI very strange. Especially since our use of WAI on the ground ( if not de-iced )is based on the Boeing flight manual and therefore SOP. (737-800)

-----------------
Track ( Legro )

[static]

Track, Let me check with the desk-jockeys.
Don`t expect any fast reply, though. Average answer out of their little kingdom takes weeks, if any at all.

[Track]

Got my OPS check coming up next week with our tech pilot. I'll question him about it.

[Hew Jampton]

Further to my earlier post, I know that one of the "major UK 737 operators" to which I referred does not have a squat switch inhibit for WAI on the ground, and I'm fairly certain that the other operator doesn't either. I find it hard to believe that this switch is a Boeing option, as usually Boeing are fairly dogmatic about how to operate their a/c, but it seems from other postings that it is indeed an optional extra. At the option of each airline, or each licensing authority? If the latter, what about JAA?

Boeing has no objection to use of WAI after anti-icing; the previously-thought idea that WAI bakes the fluid into a solid coating is not correct, apparently the fluid dries into a fine powder.

[CaptainSandL]

Thanks for your answers. I am now told that Boeing state that “wing anti-icing should compliment ground de-icing”, which would suggest that it should be put on with the engine A/I after start. Either way, it is apparent that not all of us 737 operators are using the same procedure. I was just curious if there had been a recent change of policy that I was not aware of.

PS Does anyone know if the wing A/I logic (thrust lever position, squat switch, etc) is the same across all series?

S & L

[411A]

In spite of what some may think/believe, wing anti-ice AND engine anti-ice do NOTHING on the ground without adequate bleed air, and this requires MORE that idle thrust. So, taxying around with all these systems selected ON provides NO protection. End of story :rolleyes:

[Hew Jampton]

411A, I wish it was the end of your story. What you say is incorrect, at least for the 737 -300/400/500.

[static]

411A is WRONG!

[411A]

For those that think that idle thrust will provide ADEQUATE bleed air for COMPLETE anti-icing protection for wing anti-ice or engine anti-ice on the ground will end up like "Palm 90", in the Potomic river. Wake up guys! :rolleyes:

[Hew Jampton]

I am tempted to ignore 411A but as a flight safety matter is under discussion it is important that his misleading information is not taken as gospel by anybody. Although I bow to his greater experience of the subject (of course they have much more icing in his Arizona than here in Northern Europe), his assertion that thermal anti-ice does "NOTHING" at idle is plain wrong. I note that his second posting modifies this assertion more than somewhat.

Captain SandL is, I believe, on the right lines that thermal anti-ice complements externally-applied measures, but it remains odd that some operators/states have radically different procedures and equipment options for the same aircraft (B737).

If 411A doubts the effectiveness of thermal anti-ice at idle I suggest he starts up a 737 CFM engine without a squat switch inhibit, selects engine anti-ice on, idles the engine for a minute or so (albeit it might be necessary to open the thrust lever momentarily by a small amount to open the valve at the beginning of the period, but then idle can be resumed), shuts down the engine and then puts his bare hands on the engine intake lip. If his hospital Emergency Room has email facilities, perhaps he'll let us know the result. I don't have the manuals to hand to check the details of which stages are involved, but on the CFM 737s, if bleed air from the 'normal' stage is insufficient at idle, bleed air from another stage is added. 5th and 9th stages ring a bell. Perhaps pilots of other a/c might like to add their experience/knowledge.

I can't be bothered to check the original accident investigation report just for the benefit of 411A, but I recall that a crucial factor in the Potomac accident to which he refers was that thermal anti-ice was not selected on at all, hence the erroneous EPRs etc (200 series a/c?).

[This message has been edited by Hew Jampton (edited 01 January 2001).]

[CaptainSandL]

411A

Nobody is suggesting, “idle thrust will provide ADEQUATE bleed air for COMPLETE anti-icing protection for wing anti-ice or engine anti-ice on the ground”

If you re-read my original post, you will see that we are discussing a known history of possible adverse effects vs benefits of using wing anti-icing on the ground. Over the years the advice for its use has changed, possibly more than once. The ambiguity this has created is demonstrated by the fact that operators are still divided as to its correct use.

For you to dismiss this subject in the terms you have done so, demonstrates a worryingly ostrich-like mentality and, unless you simplified your explanation for us, a poor understanding of either the system or the problem.

As I understand it, with wing A/I selected on, hot bleed air will flow to the leading edges unless either an overtemp/overpressure condition exists or if either thrust lever is advanced beyond the T/O warning setting, a thrust lever angle that I guess would probably give at least 50% N1. Even with normal taxy power settings, the leading edge will heat up. Early last year there was much discussion about the thermal stability of thin layers of de-icing fluid (see article in Aero 8, Oct 1999). The upshot of it was that because of differences in SAE and ISO standards of all, but particularly type IV, fluid it could not be guaranteed that the fluid would not have partially dried out before the hold-over time had expired.

My question is: Has this issue been sorted out yet and if so what was the conclusion?

S & L

http://www.boeing.com/commercial/aeromagazine/aero_08/deice_textonly.html

Edited to add link to Aero 8

S & L

[This message has been edited by CaptainSandL (edited 02 January 2001).]

[static]

Hew, you`re right, with the CFM 56, 9th stage compressor bleed air supplies enough pneumatic pressure at low power settings.
At higher power settings only 5th stage bleed air is used.

[FE Hoppy]

One thing no one has mentioned yet on this topic is the term "blow back" where leading edge heat simply causes moisture to run back over the wing and freeze further along the chord. This I believe is why on most? types wing de-icing is used rather than anti-icing.
This has certainly been the case on both types I have flown.

[static]

Track,

Just got a reply from our FLT TECH department.
According to them Boeing states in their manual (quote):'WAI may be used as a de-icer or anti-icer in flight only.'
This applies for 733, 734 and 738, 739

Wonder what the guys from Legro say?

[This message has been edited by static (edited 02 January 2001).]

[Silky]

And just for the sake of "correctness" the A320 family does allow wing anti ice to be selected on the ground for test purpose only and to correct m&v if I may it is for 10 seconds only. There is no limit to the amount of tests..... :) :) :)

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Gravity always wins....

[Eff Oh]

On the Boeing 757-200: (From Aircraft Manual)
WING ANTI-ICE SYSTEM
"The wing anti-ice system provides bleed air to three midwing leading edge slats on each wing. Wing anti-ice can be operated in flight ONLY. It is inhibited on the ground."
It may vary, but I would have thought all Boeings are the same?
:)
Best wishes
Eff Oh.

[JD]

Air ground sensing is there to prevent wing TAI operation on the ground,& to prevent wing structure overheat & possible failure due to lack of airflow!!! Also on B757 you can get up to 30* temp drop at the eng. inlet requiring 50% N1 every 15 min. to shed ice from the LP stators, so obviously the engine TAI is not doing the full job!!!!!!!!!!!

[ron kirkland]

Static,

The same B-737 manual states in the Adverse Weather Section, under Wing Anti-Ice Operation on the Ground,

"Wing anti-ice must be ON during all ground operations between engine start and takeoff, when icing conditions exist or are anticipated."

Warning: Ground use of the wing anti-ice is intended to complement, and not replace, ground de-icing/anti-icing and inspection procedures."

[static]

Ron,

Thanks for the info. The thing is, my company doesn`t use the Boeing manuals off the shelve. They write their own manuals, based on the Boeing books, ofcourse, but with a lot of other things added. Now it seems they may have left something out (?).
Could you give me page numbers or other references out of the Boeing manuals? Another question: is that for Boeing 733 or 732? Or NG?

Thanks

[CaptainSandL]

Eff Oh

Not only are all Boeings not the same, but also not all 737-300’s are the same! See Statics reference to a ground test position on some -300’s. Although I suspect that the rest of the system is the same.

Re JD’s comment above, again I can only speak about the 737 classics, but the air-ground sensor will only bypass the duct temp and thrust setting logic when on the ground. It does not shut off hot air to the wing simply because you are on the ground. The wings are heated on the ground, although not to the same extent as in-flight. Why else would Boeing need to change the procedure for its use on the ground if the switch position did not matter?

S & L

[Track]

Static,

My company's tech pilot referred to the same text as Ron quoted:

"Wing anti-ice must be ON during all ground operations between engine start and takeoff, when icing conditions exist or are anticipated."

BUT with the following added:

"If deicing fluids types II or IV are used WAI may be left off"

So for us the procedure is :

Icing conditions NOT deiced: WAI on
Icing conditions and deiced: WAI off

ref: Boeing 737-800 AOM Supplementary procedures, SP 16.5.

--------------------------
Track

[static]

Thanks Track,

What penalty does it give you on take off performance if you use WAI?

[ron kirkland]

Static,

The manual quoted was for an NG (-700) supp. procedures 16.5


Cheers

Ron

[CaptainSquelch]

What I've missed in the discussion so far is a bit in line with F/E Hoppy's remark on blowback. Wing Anti Ice systems normally only heat up the Leading Edge of the wing.

During operation on the ground the ice collects on the entire top of the wing during precipitaion and all the cold parts (top and bottom) of the wing during frost conditions. As we all can see every now and then during flight ice starts to collect at the leading edge, possibly spreading a bit further aft but hardly ever more than about 10 percent of the cord. Wing Anti-Ice systems are designed to clear this "In-Flight" buildup of ice. They do keep the forward 10 percent of the wing clear of ice while operating on the ground but this is not nearly enough. Before T/O I'd like to have the entire wing or at least the top free of ice, leaving room for a light frost on the bottom.

A proper de-icing treatment clears the entire wing and protects it for the length of the holdover time. If I then heat up the leading edge the glycol evaporates and I lose this protection of the forward 10 percent and trade it for thermal Anti Icing.

Apart form company rules that seem to differ on the subject: What do I loose, what do I gain? Anyone?

Sq

[pullupnow]

...please allow me to bring even more confusion to this very enlightening dicussion:
the FPPM (flight planning and performance manual) available from boeing itself for all B737 versions is calling to substract 1350 kgs (as far as I recall) from the FIELD LIMIT WHEIGHT, when using WING AND COWL ANTIICE !
Strange enough if u consider that the wing antiice valves close automatically with the application of TO thrust on all our 737,s(300,400,600,800). So it should never effect the field limit, should it ?
Obviously there there is more than one customer option flying along giving us these respectable headaces.
Whatsoever, Bombardier forbids the use of TWAI after deicing to prevent clogging (as u figured it, Sandy), and for the boeing case I am in TRACKS team, check your six !

[Hew Jampton]

Pullupnow, are you sure that decrement doesn't refer to landing? There is a 200kg decrement to RTOW for engine anti-ice, none for WAI because it trips off.

[This message has been edited by Hew Jampton (edited 08 January 2001).]

[Track]

We also correct for WAI and EAI for takeoff performance calculations:

250 kg for EAI, 1350 kg for WAI and EAI together.

The reason for the correction on WAI is not clear to me. Either Boeing thinks the trip off mechanism might fail or they think we are fast enough to switch the system back on again after liftoff but before 35 feet, since this is the end of the takeoff for performance calculations.

I'm gonna practice on the last possibility :)
--------------------
Track


[This message has been edited by Track (edited 08 January 2001).]

[pullupnow]

hehe, track, u name it.
I personally like the idea that boeing does'nt thrust it's own equipment and giving us data to cover it's s..t, but, by the way, where is our iknoweverythingaboutboeing officer on duty ?
and ,jessir, i'm shure it's not the landing field lenght.
...check your six !

[CaptainSandL]

Pullupnow & Track,

There is no reference to a wing anti-ice correction in our FFPM and, on checking the 300 CAA AFM there is no correction for field (or any other) limits. Can you find a reference for it & post it up, if it does exist we should know.

S & L