NG: Use of wing anti-ice above 35,000 feet may cause bleed trip off
 

Hi

I know you enjoy this but why to the above.

Is it because the volume of bleed air for wing anti ice and pressurisation at the same time is to much?

Thank you.

wing anti ice
 

Wing anti- ice at that level would surely be outside of the aircrafts limitation?
The solution would immediately freeze and block the capilliaries.

No, it is not outside of limitations, but the bleed demand might be too high. Which supposedly is the same reason why the outer slat isn't de-iced. So you may use it if required, but you might encounter other problems after that.

Oh, and of course it is about the 737(NG) which uses hot bleed air to de-ice wings, not any kind of solution.

I guess boeing sees the likelyhood of needing wing anti-ice at that altitude as very slim. Even ice crystal icing only seems to affect engines and heated probes.

Remember also that WAI is in fact a de-icer. To use it as an anti-icer can be very dodgy. As Denti says ice accumulation on wings LED's in ice crystal regimes is highly unlikely, and if it happens should be very minor. Once cracked off the LED should stay clean. Leaving WAI as a anti-icer, once the LED is clean, is a)unnecessary, & b) could cause flow back problems. Unlikely, but could.

I think the reason for this is the possibility of triggering a bleed trip off.

When the bleed air is insufficient or the demand is too high, more and more bleed air is taken from the 9th compression stage. This air has a higher pressure but also a considerably higher temperature hence the risk for a trip off.

This is because as we go to higher altitudes, the density of air decreases and so the engines will have to work a lot more amount than usual to cater to the bleed air requirement for anti-ice operation. Which in turn leads to an overpressure or overtemperature condition, leading to BLEED TRIP OFF light.

It's temperature that trips it.
There is a Bulletin in your FCOM which explains it.