B737 Classic- A/T de-select speed

[Mansfield]

The word "prohibit" should only appear in the Limitations section. You know, like "Use of aileron trim with the autopilot engaged is prohibited". Otherwise, I've never seen Boeing "forbid" or "prohibit" anything. This is really a social convention...in which, when you haven't got a good enough argument for why you argue some point, you default to a higher authority. Otherwise known as "appeal to authority", or argumentum ad verecundiam, a logical fallacy common enough to be discussed by St. Thomas and John Locke.

But it greatly warms my heart to see that my own training department is not alone in their ignorance of what this thing does and why...

[RAT 5]

Otherwise, I've never seen Boeing "forbid" or "prohibit" anything.

Indeed. I've flown only Boeing airliners, of various types and for various operators in different countries. It was interesting to see the differences in some procedures and use of this or that. When I asked how XYZ was allowed here, and not in my previous airline, the answer was, "we asked Boeing if they had any objection to this or that and they said no." So a 'not recommended' or some such became an OK if you asked properly.

If anyone can accept a little drift I have a few other technical questions regarding other 'not recommended' and wonder about what operators do.

[Lancelot de boyles]

After over a decade of hearing rigid responses regarding vague, or maybe 'broad' recommendations, a little thread drift might help clarify a few others.

[tdracer]

"we asked Boeing if they had any objection to this or that and they said no." So a 'not recommended' or some such became an OK if you asked properly.

Not quite - when I was still working we'd often get requests to do something other than the Boeing recommendations. We'd look at it, and if we couldn't find a reason to prohibit it, Boeing would provide an "NTO" - No Technical Objection. NTO is not the same as an OK - the NTO give Boeing plausible deniability if something does goes wrong (you didn't follow our recommendations, even though we didn't tell you that you had too). While the difference may not be important to the pilots, it's very important to the lawyers.

[RAT 5]

tdracer: Indeed, that is correct and I was less than accurate in my choice of words. It sounds like you may be able to answer some other ones then.

Back to Lance: On previous Boeings our 2 eng GA procedure was the same as a normal takeoff. An engine out acceleration was the same. i.e. a stressful less practiced manoeuvre was the same as the everyday well practiced low stress one. There are 4 profiles, takeoff EFATO, 2 eng GA, SE GA. They could all be the same but our B737 SOP's had differences. Takeoff has SOP to engage A/P at 1000'. Low stress if in crowded or claustrophobic airspace. 2 engine GA SOP to fly manually until flaps up. High workload for PF & PM, perhaps in unfamiliar airspace and with a WTF moment. Why not use A/P? Done it in the sim and it works fine: did it once on the line for airmanship reasons and it worked fine. The result is that MCP speed bug controls speed and not the flap lever, the profile is the same as a normal takeoff and the workload in an unusual manoeuvre is reduced. (And, if you have flown an A/P ILS and then GA the A/T stays engaged and the A/P disengages, are we supposed to disconnect A/T during acceleration to standardise?) SOP guys said it was due Boeing recommendation.
A common story in all my companies, and on prune, is the most screwed up simple manoeuvre is the all engine GA. Why make it different to a normal takeoff? If it was as similar as possible then perhaps less screw ups. (the same is true with RTO SOP's & calls v normal landing SOP's & calls; but that's a discussion for another day)
Same with engine failure. In sim I tried it, engaged A/P at 1000' accelerated like a normal takeoff (with less V/S) and concentrated on navigation and balancing the rudder. It was so easy to manage the NNC operation like that with a clear head. SOP was manual flight until Flaps up. Same with SE GA. You might be flying an A/P on A/T off ILS then GA manually. !000' A/P on if you require. Not allowed. Same reason given for rushing to retract flaps above 400' instead of a relaxed 1000'. Qeh? It's allowed, technically, but it's not a recommendation. Don't rush is the recommendation. Why? Boeing recommendation. Yet the ops manual suggested full use of automatics as required to improve overview and management of the operation.

I may be not quite correct with "Boeing recommendation", but that was the answer given. There maybe a Boeing 'not allowed', but that wasn't said. However the AFDS allows its selection, and it works fine in the sim, and if it reduces workload and improves overview and thus safety, why would it not be allowed? Some behind the buttons guidance and knowledge would be appreciated. Thanks.

[Centaurus]

However the AFDS allows its selection, and it works fine in the sim, and if it reduces workload and improves overview and thus safety, why would it not be allowed?

Horses for courses Rat 5. I have never understood the almighty rush to engage the autopilot after take off in normal ops, single engine go-around and non-normal like engine failure after V1. Perhaps it because the pilot is under-confident of his instrument flying ability; especially if the vast majority of his line flying is with the comfortable crutch of the automatics; whether company imposed or out of personal choice.
It becomes a matter of personal opinion but is the workload so intolerable that immediate automatics relief is necessary lest the crew cannot cope.

Forever etched in my mind was the CVR of the Middle Eastern captain screaming to his equally frightened first officer as their 737 rolled into a fatal IMC spiral dive soon after take off, of "ENGAGE THE AUTOPILOT" repeated in a flat panic, because he lacked the basic instrument flying competence to hand fly out of his self imposed unusual attitude.

[sonicbum]

Originally Posted by RAT 5

2 engine GA SOP to fly manually until flaps up. High workload for PF & PM, perhaps in unfamiliar airspace and with a WTF moment. Why not use A/P?

My guess is that a combination of high energy and low go around altitude could inhibit the AP from entering ALT ACQ, especially if the stabiliser is not properly trimmed and the pilot is "pushing" on the wheel during the manoeuvre. The pilot could then be distracted by trying to engage the AP unsuccessfully without trimming the aircraft appropriately. Of course there must be a combination of all these adverse factors but I believe Your operator wants to consider the worst case scenario. Maybe the same considerations can be applied for the remaining points.

[Denti]

It does it quite well if you did a dual channel approach. Which was the norm according to those SOPs that i have flown with. After all, one click on the TOGA button for reduced go around thrust is quite enough, especially with a low go around altitude.

[RAT 5]

The point is I've done them all in the sim; I've done it, 2 eng GA, on the line because the circumstances warranted it. The look on the F/O's face was magic. Afterwards he asked, "are we allowed to do that?" Answer, "what did you think about? It worked didn't it? Was it a good idea or not" I'm not an advocate of transferring command to the automatics; absolutely not; (control is not the same as command), but, when it is better to do so and 'manage' the scenario with a clear head then for me it is a tool. To be prohibited to use it when it is available, either by an SOP or a 'not recommended' is the discussion i want to have. I was taught to control the a/c via tactile dexterity or automatics. Taught and well practiced being the operative words. Being forbidden to do what I choose to be the best option, and is technically possible, is a retrograde step. I think we've been here before, many times. Perhaps I should retire quietly & gracefully, but having to teach, or in fact not teach, cadets on the TR courses is becoming more depressing by the session. The S.S S & S calls, loudly, I feel.

[1+F]

Agree with all that galdian has said. We used A/T ARM too, worked perfectly, no incidents, its function understood by the crews and the benefits outweigh the so called risks. Boeing just playing the lawyer game.