Minimum N1 in Anti-Icing - B737

[Zenj]

Hi,

This is my first post in this forum and I hope that I will get lot of benefits here.

In the Boeing 737-200 Limitations it's stated as follows

" Minimum N1 RPM for operating in icing conditions except for landing is , 40% when TAT between 0 and 10 degrees C,
55% when TAT below 0 degrees C, 70% in moderate to severe icing conditions when TAT below -6.5 degrees C."

Now my question is , do you put to 70% N1 when in any icing below -6.5 or it has to be this temperature plus the moderate to severe icing ?

What I mean here is that do you need both conditions for 70% N1 or just any of the 2 conditions stipulated ?

Thanks

Arif

[LEM]

Zenj, don't overthink it. If it says "moderate to severe" then it's moderate to severe!

Beware of people trying to reinvent aviation with some fancy personal interpretations.

If you know the rule and want to deviate, to be more conservative, fine.
But then don't tell other people the rule IS the way you see it.


Btw, check your Private Messages, I'd like to ask you something about an old Tanzanian friend...

;)

[lomapaseo]

Are you sure you are talking about the B737-200 and not a B737ng ?

The engines are quite different.

[Zenj]

Lomapaseo

Yes it's Boeing 737 , Series 200


Zenj

[Sawbones]

Moderate to severe icing - increase the N1 to the 70% as stipulated. Keep an eye on the wiper bolt as a reference point.

It's an abnormal situation for sure. In a normal descent through cloud you certainly wouldn't want to have to fight your way down with such a high engine rpm/EPR .. 55% is suffice most of the time.

[Cough]

As sawbones said, 70% N1 is unusual. As long as the wiper bolt isn't picking up vast amount (70% is not required for light icing) then 55% is enough.

Only went to 70% once in 5 years of operating the -200 around europe.

BTW - If you are high on the descent and you need icing on, go as fast as you can (turbulence permitting). The TAT rise may be enough for you to reduce N1 to 40%...