Boeing Icing Conditions Definition

[LEM]

Scenario: taxi and takeoff on a runway still wet after recent rain, but clear sky. Temperature 7°C.

This looks like ground icing conditions.

The exact statement is "....standing water..."

Now, do you think they mean "standing water" for what it is officially, that is more than 3 mm of water, or do they actually mean runway wet, with some water?

Depending on the points of view, egine antiicing could be mandatory, or not, for taxi and takeoff.

[BOAC]

As they say in the trade " that's why they pay you to be a Captain":D

[LEM]

Yes I know, mate, Captain judgement is not what I'm asking for,
I was wondering if a pedant knew the exact official meaning... if any. ;)

[The Greaser]

I always use icing-on for performance calculations if the runway is stated as wet and OAT < 10c. I have only flown with one captain who has not subsequently used the icing on. Seems to me that if it doesn't limit takeoff weight then better safe than sorry.

[BOAC]

With pedants hat on, this is a not uncommon paragraph for jet operators' manuals:

"Icing Conditions exist when OAT on the ground or TAT in flight is
+10°C or below and visible moisture in any form is present"

Good enough for me.:D

Time to raise the other, oft-forgotten rule? If the use of engine anti-ice is anticipated at any time before the aircraft is clean, it should be included in the RTOW calculations.

I was taught that many years ago and I've always worked to it, but it is amazing how many have never heard of it - or is it wrong.....................?

[Flight Detent]

Hi BOAC,

I've not heard of that one!

I've turned the engine anti-ice ON many times at around 300-400' after T/O, seems OK to me, works well.

But I take the point, a wet runway surface is not 'standing water' unless there are areas of, well.... standing water!

I'm talking Classic B747 here.

Cheers, FD :D

[BOAC]

I've turned the engine anti-ice ON many times at around 300-400' after T/O, seems OK to me, works well.
?? - you mean you did not crash? How do you know what your OEI performance would have been?

Well, we need JT or a similar wise-head here, but the reason, as I understand it, is that unless there is no loss of thrust with anti-ice on (ie 737-200 IIRC), then since your RTOW is predicated on obstacles up to the end of the acceleration segment, anything which degrades performance there has to be taken into acccount.

If it is not correct, I'll stop doing it!:D

Any performance experts around please?

[The Greaser]

Of course you sound absolutely correct BOAC, I must say that I have never seen this written down anywhere either.