Wing anti-ice on the ground
 

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

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.

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

Sq

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)

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).

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

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?

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.

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.

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)

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Track ( Legro )

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.

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

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.

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

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:

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

411A is WRONG!

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:

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).]

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/aer..._textonly.html

Edited to add link to Aero 8

S & L

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