WHY are two autopilots required for a go-around...

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3WE
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WHY are two autopilots required for a go-around...

Postby 3WE » Thu Mar 31, 2016 2:58 pm

...when only one is required for a Category I ILS?

Seems like a valid question.

Verbal?
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Re: WHY are two autopilots required for a go-around...

Postby PurduePilot » Sat Apr 09, 2016 5:13 am

Which model?

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Re: WHY are two autopilots required for a go-around...

Postby Gabriel » Sat Apr 09, 2016 5:27 am

Which model?
B-737 NG

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Re: WHY are two autopilots required for a go-around...

Postby PurduePilot » Sun Apr 10, 2016 8:32 pm

Don't know... where did you hear that?

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Re: WHY are two autopilots required for a go-around...

Postby Gabriel » Sun Apr 10, 2016 10:29 pm

Don't know... where did you hear that?
One example.

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Re: WHY are two autopilots required for a go-around...

Postby PurduePilot » Sun Apr 10, 2016 10:56 pm

Below 200 ft you don't want to be on a single channel because there's not enough margin for the pilot to react to an AP error (e.g. unexpected pitch down). This applies in APP mode or GA mode. I'm not specifically familiar with the 737 setup but if you are in APP mode below 200 ft in dual channel mode and one channel fails, it probably allows you to continue on the remaining channel rather than having an unexpected disconnect at 50 feet AGL.

Newer models have 3 channel autopilots.

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Re: WHY are two autopilots required for a go-around...

Postby 3WE » Mon Apr 11, 2016 2:33 am

Hey Gabe...I'm thinking that it's kind of a black and white thinking thing...

Maybe we do want 2 autopilots for Cat III ish kind of stuff including a critical go around at 50 or 20 whatever feet....

...just for those 10 to 20 critical seconds...

So because of that, they designed it for all instances when the TOGA easy button is pushed, better have double Ottos, even if it's a non rocket surgery go around with hundreds of feet of buffer.

???
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Re: WHY are two autopilots required for a go-around...

Postby Gabriel » Mon Apr 11, 2016 4:07 am

Below 200 ft you don't want to be on a single channel because there's not enough margin for the pilot to react to an AP error (e.g. unexpected pitch down). This applies in APP mode or GA mode. I'm not specifically familiar with the 737 setup but if you are in APP mode below 200 ft in dual channel mode and one channel fails, it probably allows you to continue on the remaining channel rather than having an unexpected disconnect at 50 feet AGL.

Newer models have 3 channel autopilots.
Nobody argues that. The problem is what, at first sight, seems to be an inconsistency in the design logic.
HAL: Sorry Dave, I cannot flare and land on single AP.
HAL: Sorry Dave, I will not fly your plane on a single AP if you choose to go around below 2000ft.

But...

HAL: Fly an approach down to 50 ft in solid IMC on a single AP? Sure!!!

Maybe the question here is not why are 2 AP required for a GA below 2000 ft, but why is only one AP required for an approach down to 50ft (and maybe, why, according to the above document, 2 APs are not even allowed in any other phase of flight other than approach or GA, I guess that a sudden push down, or pull up, at 400 ft right after take-off would not be nice either).

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Re: WHY are two autopilots required for a go-around...

Postby 3WE » Mon Apr 11, 2016 6:20 pm

Below 200 ft you don't want to be on a single channel because there's not enough margin for the pilot to react to an AP error (e.g. unexpected pitch down). This applies in APP mode or GA mode. I'm not specifically familiar with the 737 setup but if you are in APP mode below 200 ft in dual channel mode and one channel fails, it probably allows you to continue on the remaining channel rather than having an unexpected disconnect at 50 feet AGL.

Newer models have 3 channel autopilots.
Nobody argues that. The problem is what, at first sight, seems to be an inconsistency in the design logic.
HAL: Sorry Dave, I cannot flare and land on single AP.
HAL: Sorry Dave, I will not fly your plane on a single AP if you choose to go around below 2000ft.

But...

HAL: Fly an approach down to 50 ft in solid IMC on a single AP? Sure!!!

Maybe the question here is not why are 2 AP required for a GA below 2000 ft, but why is only one AP required for an approach down to 50ft (and maybe, why, according to the above document, 2 APs are not even allowed in any other phase of flight other than approach or GA, I guess that a sudden push down, or pull up, at 400 ft right after take-off would not be nice either).
...being my normal lumpy self, I'd prefer a fundamental over-riding general rule to be 'always' two autopilots for any sort of halfway critical approach activity or anything done within 1000 feet of the ground/whatever....That you even need two autopilots to take over shortly after liftoff on a normal takeoff when you go click clack paddywhack in reverse?

In an 'emergency', then you could do your single autopilot ILS, but the EVAN emergency memory checklist would call for super incredible extreme monitoring and the warning that all other automatic stuff (like what comes next if we go missed or the actual landing), is done manually....

(Just going after nuances...I hate unnecessary nuances when guys are busy shooting approaches in tough weather when they are dog tired...(because I understand human factors more than Evan does)).

All that being said, did I read correctly that the conditions around the Flydubious crash were such that they were supposed to hand fly the approach anyway???...it's sad if confusion over one versus two Ottos at the time of go-around is a contributing factor...and it's still easy for me to imagine something like that...Ok, positive rate, gear up, and I pushed the easy button...yawn...oh shit. :-(
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Re: WHY are two autopilots required for a go-around...

Postby PurduePilot » Mon Apr 11, 2016 10:58 pm

Gabriel, where do you get the idea that you can go below 200 ft on a single channel?

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Re: WHY are two autopilots required for a go-around...

Postby Gabriel » Tue Apr 12, 2016 3:37 am

Gabriel, where do you get the idea that you can go below 200 ft on a single channel?
For example, same link as before. Where do you get the idea that you can't? Or, at what altitude do you suggest that the single AP flying the ILS approach in solid IMC would or should self disengage? I would not see that as a good idea either.

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Re: WHY are two autopilots required for a go-around...

Postby 3WE » Tue Apr 12, 2016 3:51 am

Gabriel, where do you get the idea that you can go below 200 ft on a single channel?
For example, same link as before. Where do you get the idea that you can't? Or, at what altitude do you suggest that the single AP flying the ILS approach in solid IMC would or should self disengage? I would not see that as a good idea either.
Brad (and Gabe):

Don't get hung up over 200 feet vs. 50 feet...

At issue is that (according to Gabe's link) if you hit TOGA below 2000 (that's two thousand) and you are only on one autopilot, it will disconnect.

There seems to be at least some lack of logic to that- If one autopilot will do an ILS to whatever altitude (500 feet just for argument), what's so damn tricky about a healthy transition from an 800 fpm descent to a 2000 fpm climb with a 500 or 1000 or 1,500 ft buffer?

There's an unsubstantiated parlour talk speculation theory that the AP switched off when the Flydubious pilots hit TOGA and they either missed it and/or it tripped them up / into disorientation and loss of control.
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Re: WHY are two autopilots required for a go-around...

Postby flyboy2548m » Tue Apr 12, 2016 4:21 pm

I would not see that as a good idea either.
Nobody cares what you see as a good idea, Gabriel. In fact, nobody cares what you think period.
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Re: WHY are two autopilots required for a go-around...

Postby Not_Karl » Tue Apr 12, 2016 5:10 pm

In fact, nobody cares what you think period.
I do.
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Re: WHY are two autopilots required for a go-around...

Postby Gabriel » Tue Apr 12, 2016 5:12 pm

Nobody cares what you see as a good idea, Gabriel. In fact, nobody cares what you think period.
You want to say something to me? Then go on and say it.

Just please, for the sake of respect, don't put your words in everybody's mouths. You don't know what everybody care or don't care and nobody appointed you as everybody's representative.

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Re: WHY are two autopilots required for a go-around...

Postby 3WE » Tue Apr 12, 2016 5:56 pm

...You want to say something to me? Then go on and say it...
Well @#$T%! Since I seem to be looking for hidden meanings so much these days:

Maybe what Flyboy and ITS and Boeing Bobby and others have said to you and me and Evan and others (more than once) is, "Go easy on the pontificating about what's wrong and the things we* need to fix in aviation. Not only do we* try hard to keep things safe, we've* usually already thought about this stuff and made a sound decision of what's best (albeit not perfect for all circumstances)...and as a result of this, aviation is extremely extremely safe."

*We is we insiders who actually devote 100% of our time to aviation and safety, we is NOT YOU (Gabe, 3BS, Evan, Tee Vee, others) who parlour talk on aviation forums and act like big experts.

I try, with limited success, to express this subtle difference in attitude.
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Re: WHY are two autopilots required for a go-around...

Postby flyboy2548m » Tue Apr 12, 2016 7:19 pm


Just please, for the sake of respect, don't put your words in everybody's mouths.
I don't owe you any respect, Gabriel. Neither does anyone else.
"Lav sinks on 737 Max are too small"

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Re: WHY are two autopilots required for a go-around...

Postby flyboy2548m » Tue Apr 12, 2016 7:23 pm

...You want to say something to me? Then go on and say it...
Well @#$T%! Since I seem to be looking for hidden meanings so much these days:

Maybe what Flyboy and ITS and Boeing Bobby and others have said to you and me and Evan and others (more than once) is, "Go easy on the pontificating about what's wrong and the things we* need to fix in aviation. Not only do we* try hard to keep things safe, we've* usually already thought about this stuff and made a sound decision of what's best (albeit not perfect for all circumstances)...and as a result of this, aviation is extremely extremely safe."

*We is we insiders who actually devote 100% of our time to aviation and safety, we is NOT YOU (Gabe, 3BS, Evan, Tee Vee, others) who parlour talk on aviation forums and act like big experts.

I try, with limited success, to express this subtle difference in attitude.
Isn't it amazing that an agronomer understands that but one of our time's leading aerodynamicists does not?
"Lav sinks on 737 Max are too small"

-TeeVee, one of America's finest legal minds.

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Re: WHY are two autopilots required for a go-around...

Postby Not_Karl » Tue Apr 12, 2016 7:51 pm

Guys, pretty please, be nice and play it friendly (or was it "be friendly and play it nice"?) :mrgreen: .
Let's try to enjoy this little place Monchie selflessly keeps for us ;) .

Don't force 3WE to use his red pen :mrgreen: ,

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Re: WHY are two autopilots required for a go-around...

Postby Gabriel » Tue Apr 12, 2016 10:10 pm


Just please, for the sake of respect, don't put your words in everybody's mouths.
I don't owe you any respect, Gabriel. Neither does anyone else.
Well, that clearly marks the contrast between us. I think every body deserves respect from you or anybody else.

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Re: WHY are two autopilots required for a go-around...

Postby Gabriel » Tue Apr 12, 2016 10:33 pm

Well @#$T%! Since I seem to be looking for hidden meanings so much these days:

Maybe what Flyboy and ITS and Boeing Bobby and others have said to you and me and Evan and others (more than once) is, "Go easy on the pontificating about what's wrong and the things we* need to fix in aviation. Not only do we* try hard to keep things safe, we've* usually already thought about this stuff and made a sound decision of what's best (albeit not perfect for all circumstances)...and as a result of this, aviation is extremely extremely safe."

*We is we insiders who actually devote 100% of our time to aviation and safety, we is NOT YOU (Gabe, 3BS, Evan, Tee Vee, others) who parlour talk on aviation forums and act like big experts.

I try, with limited success, to express this subtle difference in attitude.
f*** you. Now, look for the hidden message there.

I don't know if you noted that he said "Nobody cares what you think period".

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Re: WHY are two autopilots required for a go-around...

Postby Gabriel » Tue Apr 12, 2016 10:38 pm

...You want to say something to me? Then go on and say it...
Well @#$T%! Since I seem to be looking for hidden meanings so much these days:

Maybe what Flyboy and ITS and Boeing Bobby and others have said to you and me and Evan and others (more than once) is, "Go easy on the pontificating about what's wrong and the things we* need to fix in aviation. Not only do we* try hard to keep things safe, we've* usually already thought about this stuff and made a sound decision of what's best (albeit not perfect for all circumstances)...and as a result of this, aviation is extremely extremely safe."

*We is we insiders who actually devote 100% of our time to aviation and safety, we is NOT YOU (Gabe, 3BS, Evan, Tee Vee, others) who parlour talk on aviation forums and act like big experts.

I try, with limited success, to express this subtle difference in attitude.
Isn't it amazing that an agronomer understands that but one of our time's leading aerodynamicists does not?
Well, if that was really what you meant to say, then let me remind you that this is an open internet forum called Airdisaster.info.

Can you or somebody else please spoon feed me and tell me what is the purpose of this forum? Because if it is that nobody can express their opinion, or that nobody cares about anybody's opinion, then I don't see the point.

Why to you bother to participate at all to begin with?

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Re: WHY are two autopilots required for a go-around...

Postby flyboy2548m » Wed Apr 13, 2016 7:06 am

Well, that clearly marks the contrast between us. I think every body deserves respect from you or anybody else.
You're wrong. Respect is earned, and in the 10+ years that I've been reading your priceless compositions you've done absolutely nothing to earn mine.
"Lav sinks on 737 Max are too small"

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Re: WHY are two autopilots required for a go-around...

Postby 3WE » Wed Apr 13, 2016 1:56 pm

...Now, look for the hidden message there...
Sadly, there are several.
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Re: WHY are two autopilots required for a go-around...

Postby 3WE » Wed Apr 13, 2016 2:54 pm

Isn't it amazing that an agronomer understands that but one of our time's leading aerodynamicists does not?
We need to do a better job of growing healthy, organic, non-GMO, fertilizer-free and pesticide-free food...of course what sometimes happens when we use beautiful, natural, hormone- and antibiotic-free BS to fertilize lettuce?...You should see the crap on the Professional Agronomist Rumor Network discussion fora!
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