B737NG 15degrees AofB

[Pin Head]

My colleague has it selected for the whole flight. Take off, cruise and approach.

I am sure he is break a rule of the air by not having 25 set.

Am I right?

[wanabee777]

Isn't there an "Auto" position??

[FlyingStone]

Ask him to read ICAO Doc. 8168 carefully and to tell you at which bank angle are all IFR procedures calculated. He might be quite surprised. On top of that, it only affects HDG SEL and VOR/LOC modes, so the autopilot will still bank up to 30° AOB in cruise while in LNAV.

[Denti]

Isn't there an "Auto" position??

Nope, it will use automatic adjustment of AoB in LNAV and VORLOC, but in HDG it will use the AoB selector setting, which is adjustable between 10° and 30° in 5° increments with the standard setting being 25°.

[olmedo]

The limitation does only apply if you are using HDG SEL during an Engine Failure or during the Cruise close to the Opt/Max Altitude. LNAV is AoB protected tough and will use whatever it needs even if you have it in 15 degrees AoB
It is a protection that couples with the F/D as part of the AFDS.

Hope you find it useful

[Pin Head]

Yes I understand all of that. They set it on departure just in case they get engine failure and need for emergency turn. But they leave it at 15 all the time.

I convinced that all sids and stars with headings are all worthless now.

Just need a reference to show him that he is wrong.

[olmedo]

Default setting for AoB selector is 25 degrees. During normal operation is not inteded to go beyond 25...max 30 degrees.

Each company SOP's may have different Default AoB, it is out of my scope.

[FlyingStone]

Nope, it will use automatic adjustment of AoB in LNAV and VORLOC, but in HDG it will use the AoB selector setting

I was under impression that AoB selector influences both HDG SEL and VOR/LOC modes.

Just need a reference to show him that he is wrong.

Well, a general read of Doc 8168 Vol. 1 (http://code7700.com/pdfs/icao_doc_8168_vol_1.pdf) wouldn't hurt, but table I-2-3-1 in Chapter 3 should be the main reference.

[B737SFP]

FlyingStone... And you were right.

The Bank Angle Selector DOES affect the VOR/LOC mode. Try capturing the localizer with the bank set to 10 degrees and see what happens.

(But don't try it somewhere with parallel runways, just a friendly advice) :ok:

[Centaurus]

My colleague has it selected for the whole flight. Take off, cruise and approach.


Just another gimmick for goodness sake. You don't need a flight director to tell you to fly a bank angle of 15 degrees. You can easily see 15 degrees on the PFD unless you are so totally automatics addicted that you need a flight director to fly an aeroplane.

The statistical chances of having an engine failure on take off at the exact position where a curved take off starts and at a speed where you need exactly 15 degrees angle of bank, are so small that you could go through your entire career without it happening. And to have the selector set to 15 degrees in all stages of flight is nothing short of puerile thinking. Superfluous SOP's are the bane of this industry.

If it does happen while your angle of bank limiter is set to the normal 25 degrees, it takes less than a second for the selection to be made to 15 degrees if you are unable to operate without the aid of a FD. :(

[latetonite]

Well that's a bit far fetched. In this case you are still in HDG SEL mode, not VOR/LOC.

[RAT 5]

PinHead: Ask your colleague to explain his reasoning behind this selection. Consider it and then come back here and tell us. Then we can make informed judgements and advise you.

[latetonite]

As long as people try to fly planes by SOP's only, without understanding the basics, I am afraid this type of questions will pop up more.