744 icing detection x actual icing condition
 

Hi,

Have a question concerning 747 A/I operation:

Scenario

- EICAS alert message: >NO ICING

However ...

- TAT is inside 10ºC to -40ºC range, there is visible moisture, etc.

Should nacelle anti-ice be on or off?

Thanks.

In descent, ON.

In climb or cruise, AUTO if available. ON if Auto not available; also a good option especially if you can't see the nacelle to check visually (cloud is too dense and/or wing lights don't work).

I agree on descent, in this case with visible moisture, leave it on. EICAS will prompt ' >ANTI-ICE' if TAT greater than 12C. I've had that ' >NO ICING' flick on and off many times when still technically in the range.