B-737 HDG SEL for trimming

[Rusobalt]

Hello
What for we have to push HDG SEL before trimming?
10X

[Dufo]

Reason is not to turn, so you can eliminate the sideslip. I suppose you mean the 'primary rudder trim technique'.

[Banana Joe]

I did not get the question and I still don't. HDG SEL is an AFDS function, what kind of trimming are you talking about?

[CHfour]

The 738s that I fly usually need a bit of left rudder trim on takeoff and some right trim as we climb into cooler air. According to Boeing it's caused by the contraction of the control cables as the aircraft cools and should not be trimmed out. Some pilots are quite happy to sit all day with the control wheel skewed but I always trim it out. We're supposed to select HDG to assure the wings are level but I do it in LNAV provided we're not turning.

[Chesty Morgan]

The main reason to trim in HDG is because LNAV follows a track and, therefore, the heading will change with wind changes. You can’t then be sure that the reaction of the control column is due to you trimming or wind change.

In HDG this won’t happen.

[Rusobalt]

Originally Posted by Chesty Morgan

The main reason to trim in HDG is because LNAV follows a track and, therefore, the heading will change with wind changes. You can’t then be sure that the reaction of the control column is due to you trimming or wind change.

In HDG this won’t happen.

THANK YOU!