Arming both ap for approach
 

Hello folks,

Regarding arming the autopilot for approach: why do we arm both autopilots for a normal cat I approach? On the 737 we always flew with the pf autopilot the ils. So is it because we could forget it?Or any technical reason?
Thanks!!

I don't know for which aircraft are you asking but on 737 if you arm both AP for approach, you get quite a bit of nose-up trim at ~ 400ft RA to help the aircraft with flare in autoland and could come as a nasty surprise as you disconnect the autopilot at Cat 1 minima in marginal weather for manual landing. I believe this is the reason why most operators choose to fly ILS approaches with only one autopilot unless conducting autoland.

For the 737 Classics anyway there was never a Boeing requirement to use both AP for a Cat 1 ILS. It was two autopilots only for an autoland which is not required for a Cat 1. Some chief pilots are very fond of publishing their own particular egos in company operations manuals. Sounds like the problem exists in your operation. :E

Because that is standard Airbus factory sop.

At least on the classic 737 fleet, flying the ILS with 2 APs will give you the chance to do a go around with autopilot. So must guys that fly ILS with the 2 APs do so to reduce workload in case of a go around, it wasn't a SOP on my previous outfit but rather a personal choice.


Cheers

It was a SOP in the airlines i have flown the 737, both the classic and the NG. Originally the reason given was to prevent an aileron hardover, a few of which happened before that SOP was introduced. But of course the easier auto-go around is another reason. And of course, the only chance for an FO to fly an autoland was during CAT I conditions, which is an approved procedure.

What could be more simpler for the average pilot than an all engines manual GA? No chance of an aileron hard-over there. After all, a one engine inoperative GA is flown manually so what's all the sweat about a two engine manual GA? You don't need a flight director for either. Unless of course one is the victim of automation addiction.

What could be simpler? Pressing one button.

Why? I mean, automatic go around is available in a one engine inoperative scenario, same as autoland to CAT IIIa standards.

And yes, of course a dual engine go around is simple enough to fly without any help, but is very rarely trained and very uncommon in normal flight operation. And then, it is not that simple anymore if the last time you did it was 10 years ago during your initial type rating...

I'm curious why Speedwinner asks the question on here and not to the in-house training dept. When the answer is given please inform us; plus was type you are on. It always help to be complete with the specific type in questions.

Sorry! A320! Have been on the 737 and now 320

not recommended in the FCTM or mentioned for a normal cat 1.

would be hesitant to do it.

views?

Again...on which type?

So the goal of my question was: why do we arm on a a320 Airbus aircraft both ap in a cat1 approach?

Pure guess here...so shoot me down....haven't looked it up....(A320 related by the way)

Could it be so that in the case of an FMGC failure (FMS), and one AP 'kicks out', that we automatically have a downgrade from CAT 3 DUAL, to CAT 1 using the remaining AP (1 or 2) and still able to continue the auto flight regime down to CAT 1 minima....

I'll get my coat lol....

F/o

What defines a "classic" 737? Seems like that would be the old clunker that had only one primitive auto-pilot. I never flew any model of the 737 but I did fly the 727. It had a lousy auto-pilot. Then, the advanced 727 came along with a slightly less lousy auto-pilot that was supposedly good for limited CAT III with a DA. It didn't auto-land. It just flared (sort of).

classic = 737-300/400/500 series.

it has an advanced autopilot capable of autoland, unlike the original series 737-100/200

BOEING 737 NG

Follow the FCOM and company policy.
 

Follow the FCOM and company policy.

In the NG it is virtually always best to use the best and full protection of the AP which is derived from using FAIL OP (with EDFCS) or dual channel FAIL PASSIVE for pre-EDFCS APs without LAND 3 capability.

The failure tolerance and protection against AP anomalies is vastly superior when using the best AP mode possible, which is achieved by using both APs.

Bottom line is follow the FCOM and company policy.

On the NG, ...EDFCS with using either LAND 3, or LAND 2 is an amazing robust system... and even the earlier dual-channel Fail Passive system was quite good.

Fairly sure I have been in a -200 (jurassic BTW...) for a Cat III autoland.

As for A320, I don't think it matters for CAT I conditions. However, if you arm both for every approach, muscle memory means you'll arm both when it counts (real CAT IIIb conditions...)

This discussion becomes rather irrelevant in more modern Boeings...:ok: