Wing Anti-Ice on Ground

[STBYRUD]

Hey folks, we recently had a debate at the company about the use of WAI on ground (737Ng in this case). I have trouble coming up with a scenario in which heating the inner three slats would be sufficient to protect the aircraft from icing during taxi - the way I see it is that in proper icing conditions on the ground there is no way around chemical anti-icing (which in turn of course would mean not turning on WAI). Same story during taxi in, keeping WAI on will keep roughly half the leading edge free of deposit but will also not save you from de/antiicing the bird before the next takeoff. Thoughts?

[Occy]

dunno 'bout the maggot, but on the b767 and b744 WAI is inhibited on the ground.

[SMOC]

The aluminum leading edge is not designed to be heated without airflow over it.

Which is also the reason the 747 cannot use WAI with the LE flaps extended as they mask the airflow over the actual leading edge. The tube which blows air onto the inside of the LE is made from titanium.

I believe 737s with the WAI 'test' position switch had ground WAI inhibited like the 747. Not sure what the difference in the system is between the two versions of WAi on 737.

[STBYRUD]

Thanks boys, that is part of the reason why I asked in the first place, I guess the 737 is quite unique in that Boeing explicitly allows using WAI on ground (SP-Adverse Weather)... And I just cannot see a good case for it.

[Kuchan]

The WTAI system may operate in flight or on the ground.
(Classic has a GND TEST position ).

The heated air flows to the three inboard leading edge slats.
Overheat switches in each wing leading edge, protect the slats
from overheat. This overheat protection operates only when the
airplane is on the ground.

When the wing thermal anti-icing system is used on the ground,
there is very little cooling airflow over the wing. In these
conditions, the wing thermal anti-icing system heat output can
overheat the wing leading edges. This can damage the heat
treatment of the leading edges devices.

Switches on the control stand close the WTAI valves when you
advance the engine thrust levers. This conserves engine thrust
for takeoff. This thrust conservation protection only operates
when the airplane is on the ground.

The air/ground logic gives the wing anti-ice system air ground
sense feedback. The engine and wing anti-ice module uses this
feedback to enable overheat and thrust conservation protection
for the wing anti-ice system. It also turns off the WTAI system
during takeoff.

[stator vane]

a certain airline, whose aircraft are blue and white with a bit of yellow on the vertical stab, still think that lives will be lost if one does not turn on wing anti-ice whenever you turn engine anti-ice on, unless of course you have recently been de-iced with type 2 or above.

but they are very good at creating lots and lots of things to do that don't really make sense.

and it is not good form to ask "why?"

much like going through security--

but i still keep asking "why?" whenever i am made to take my shoes off, or my ipad is scanned for explosives, or when they ask, "do you have anything sharpe on you?"

sorry, off thread a bit. most likely this will be removed soon. though all are definitely aviation day to day related.

one of the un-fathomable "THREATS" that we all are expected to cant like the Lord's prayer.

[Denti]

We actually had the same procedure even on our classics (300/500) as they had the same WTAI system as we now have on our NGs (and the same digital pressurization system too).

But i can't remember if there ever was a justification to heat up all slats (classic) or the inner three slats (NG) on the ground. But it's always a nice distraction to watch those nice blue lights toggling between bright and dim blue when being nr. umpteenth for take off.

[EW73]

I'd just like to clarify the abovementioned statement re the 737NG that says: "It also turns off the WTAI system during takeoff." referring to the thrust lever advancement for takeoff, whilst on the ground, which is a bit misleading as stated, as I read it, let me explain...

In essence the statement is correct, and is also highlighting one of the anomalies in the 737NG indicating system, IMHO.
Another statement further down, said "But it's always a nice distraction to watch those nice blue lights toggling between bright and dim blue when being nr. umpteenth for take off."
You may notice that 'those little blue lights' don't actually go out when the t/lever(s) are advanced, they go from 'dim' (valve open) to 'bright' (valve not in the position selected by the control switch), and stay at bright until either:
1/ the aircraft transitions to flight mode, at which time the control switch goes to OFF, and the bright blue lights immediately go out (since the valves are closed already), or
2/ the takeoff is aborted, at which time the t/levers are returned to the idle position, and both the bright blue lights return to dim, as the two WAI valves reopen, as directed by the control switch, which is still selected ON.

If WAI is deemed necessary immediately after takeoff, the system needs to be re-selected in the flight mode, which basically just bypasses the overheat sensors for flight operation.

So my clarification revolves around the WAI system is not really 'turned off' during the takeoff, as such, simply temporarily monitored off for the duration of the normal takeoff ground run!

The anomaly for me revolves around the fact that the WAI system is monitored off during takeoff as a part of the normal operation of the system, but the indication reflects the valves are not in the position required (bright blue), which is not really the case, as they are under the control of the throttle quadrant switch pack!

Just seems different, or maybe it's just me!

Cheers...EW73 :bored:

[Denti]

The cycling is usually a result of the thermal switch, not of TLA. I always see the bright blue as an indication that yes, there is a disagreement between commanded position and actual position, but there is a good reason why. For example too high temperatures or a TLA that will command the switches to off.

Still seems somewhat odd and most probably could have avoided with a more advanced cockpit layout in the NG which was sadly voided after southwest were against its, same for the coming MAX by the way.

[aterpster]

In addition to the issue of overheating and compromising the affected annealed wing structure WIA is ineffective on the ground because the snow or freezing rain that falls on the top of the wing is unaffected by WAI.

[ImbracableCrunk]

My company says that, if you need WAI on the ground, then you need fluid. If you have fluid, you don't use WAI. So. . . don't use WAI on the ground, just get sprayed.

I believe the airmode-unlatch for WAI is a customer option.

[Notso Fantastic]

Spent years flying 737 in BA always totally banned from ever using WAI on the ground. Then I fly for Ashtrays-r-us and it's a fail if you ever use engine de-icing on the ground without WAI. Totally confused. I always planned to enquire why one day, but they went the way of Globespan and XL (and others) to that place in the sky with 70 virgins! Indeed 'tis a mystery!

[Denti]

Interesting, as a subsidiary of BA it was the same as with Astraeus for us. Always switch on all or nothing on the ground. As i said above, dunno if there was ever a reason for that.

[BobnSpike]

WAI on the 777 is normally automatic, activated by the detection of icing conditions. Manual and automatic operation is inhibited on the ground.

Automatic operation is inhibited for 5 minutes after takeoff if the TAT is greater than 10C. It is also inhibited for 10 minutes after takeoff if the thrust is in a takeoff mode.

I flew an EMB 145 in a past life. The WAI was automatic on that as well. Operation was inhibited below 25 knots wheel speed on the ground so as not to overtemp the leading edges. When taxiing in greater than light frozen precip or even sometimes heavy rain, the ice detectors would sense icing conditions but the WAI valves would not open due to the speed inhibition. This produced a nuisance EICAS warning: ICE COND WING AI INOP (red with three bells). Usually this was not a big deal as it was a known issue, but it took 30 seconds to clear. When holding in position or cleared for takeoff it could be a pain.

[BOAC]

As with Notso and Denti, I did try to persuade Asparagus that using mandatory wing antice with an OAT of 9.9 degrees (in mist/rain) was a little odd but it fell on deaf ears.:)

[SMOC]

A mate fwd this to me.

Wing Anti Ice

Wing anti-ice (WAI) is very effective and is normally used as a de-icing system in-flight, in applications of 1 minute. On the ground it should be used continuously in icing conditions.

The WAI switch logic is interesting, on the ground, bleed air for WAI will cut-off if either thrust lever is above the take-off warning setting, but will be restored after the thrust is reduced. This allows you to perform engine run-ups etc without having to check that the WAI is still on afterwards. The switch is solenoid held and will trip off at lift-off, this is for performance considerations as the bleed air penalty is considerable.

Note that on early systems, ie those with a GND TEST position, with the WAI switch ON on the ground, the WAI is inhibited until lift-off ie "armed", This is opposite to the present system.

WAI, unlike engine AI, uses bleed air from the main pneumatic manifold, this is to ensure a source of bleed air during engine out operations. Only the leading edge slats have WAI (ie not leading edge flaps). The NG series outboard slat has no wing anti-ice facility (see photo) believed to be due to excessive bleed requirements. However in June 2005 it was announced that the 737-MMA will have raked wingtips with anti-ice along the full span. This is because the MMA will be spending long periods of time on patrol at low level where it will be exposed to icing conditions.

NB Where QRH ENGINE FAILURE/SHUTDOWN drills ask “If wing anti-ice is required:”, if icing conditions are anticipated, these actions should be completed in preparation for WAI use to prevent asymmetric application. There is no bleed penalty for this reconfiguration until WAI is actually used.

On the NG, if WAI is used for more than 5 secs in-flight, the SMYD will adjust the stick shaker speeds and manouvre speed bars to allow for airframe ice.

[STBYRUD]

Thanks folks, good to see that I am not the only one who questions this procedure... Thanks especially to IGh, I suppose you have found the reason for this nonsense! To recap, there is nothing to be gained from heated slats when the rest of the wing freezes up on ground until some CAA gives an operator a new clean wing definition that happens only to cover roughly half of the leading edge...

[Ice-bore]

The post 'Air Florida' mod, to enable the 737 to use WAI on the ground, was rejected at the time by a number of European Airlines, due to the effect that the hot surface (103 deg. C on the ground) had on the 'thickened' (Type II) de-/anti-icing fluids that were widely in use in Europe at the time.

The heated L/E rapidly evaporated the water present in the fluid, leaving a thick gel like substance on this critical surface.

[PantLoad]

No problem....

As long as a few slats are clear of ice, the airplane will fly just fine
with the other slats, all flaps, and the wings (proper) completely covered with ice and snow. Doesn't everyone know this!!!!!!!

And, of course, the above is perfectly legal, too!!!!!


NOT!!!!

You've got to be sXXXXXg me!!!!!!


Fly safe....or try to, if you can,


Pant:Load