Wing anti icing

[Icing]

I was wondering if somebody on this forum has experience with icing conditions on the Boeing 747. The AOM states that during icing conditions in a holding, the holding should be performed without slats extended. The reason for this is that the effect of your wing anti ice system is neglectable with slats extended. Therefore my question is what happens during the approach in icing conditions, where flaps (slats) must be extended. The same counts for take-off, where icing conditions start at ground level (assuming that the anti-ice fluid will leave the aircraft during rotation).

I hope somebody can help me regarding this "topic"

Thanks in advance

[Flight Detent]

Hi Icing,
My experience here is that if icing is encountered during the descent, you use the engine anti-ice systems as advertised, with the minimum N1 RPM (depending on the engine type).
With the de-ice systems, either one of the pilots, (with the FEs promting), looks out and checks the wings LEs (retracted), for the build-up of ice, and uses the bleed air to dislodge that ice, then turns off the bleed, and wait for more build-up, that way, the ice only builds up on the LE, not the upper/lower surfaces.

I agree, holding in icing conditions, no LEs, and use de-icing system as required, each 'burst' of LE bleed air lasts only for about 20-25 seconds to do the job.

Anticipation is the secret here, when you are manourvering to start the approach, just prior to selecting flap one, give the LEs a de-ice cycle, and that has to last until touch down.

Cheers

[Intruder]

In almost 5 years on the 744, I've never had to use wing anti-ice.

However, in the rare cases where you do need it, holding and descent should be done with flaps up, and flap extension delayed as long as possible to minimize your time exposure to icing conditions without anti-ice available. Generally, approach holding is at a weight where max holding speed can be accomplished with flaps up. If icing is a problem and holding speed is lower than flaps-up maneuvering speed, tell ATC you need a higher airspeed. Declare an emergency if necessary.

Icing (especially moderate-severe icing) usually occurs in relatively narrow altitude bands. Once you start the approach, you will more likely than not descend out of the icing you had at holding altitude.

[Icing]

Thanks so far for the replies!!!
Really interesting to hear how you deal with flap (slat) extension in icing conditions. Does somebody have experience with the same "problem" on other aircraft types.

All info is welcome!!

Greets,
Icing