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Old 19th Jun 2017, 21:16   #21 (permalink)
 
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I can see the attraction of doing things in advance. Pre-setting an altimeter has to be a good thing if a. It is recommended by the manufacturer and b. It doesn't change your path. But if it's not a recommendation and/or your flight path is changed then it's a silly thing to do. But some pilots like making up their own procedures and these DIY procedures are a bloody pain in the bum, especially in the sim. The torturers in there make your life difficult enough without you or partner scoring own goals. It's also not a good idea in the real thing.

With regard to your height encoding I'm not so sure this is affected by any settings made by pilots. The height information is always set on Standard. But many aircraft will rapidly change level with the autopilot on if the side in control side has its altimeter quickly flicked to another setting. And this will generate a TCAS alert.
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Old 19th Jun 2017, 21:20   #22 (permalink)
 
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Originally Posted by PENKO View Post
Which SOP are you referring to?
I really don't know what you're talking about . . . .
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Old 20th Jun 2017, 00:27   #23 (permalink)
 
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From Eurocontrol

https://www.eurocontrol.int/faq/how-...-and-other-qnh


How does ACAS II work if one aircraft is using the standard altimeter setting and the other QNH?

ACAS II always utilises pressure altitude information which relates to the standard pressure (altimeter setting 1013.25 hPa). ACAS II operation are not affected if aircraft are flying Flight Levels on the standard pressure setting, altitude on QNH, or height on QFE as the same pressure setting (i.e. standard) is always used.

The pressure selection by the flight crew does not affect the ACAS II system at all. Additionally, below 1750 feet ACAS II also uses radar altimeter data
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Old 20th Jun 2017, 08:31   #24 (permalink)
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Originally Posted by PENKO View Post
Nope. The AP will hold the memorized ALT. Besides, we wouldn't have this topic if the AP would chase the new indicated altitude.
That depends on type.
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Old 20th Jun 2017, 18:01   #25 (permalink)
 
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As mentioned,787 allows you to preset without actually referencing.
When is this handy,..in my mind,when over terrain with MORA above 10,000'
When the training captain enquiries why you have preset an area QNH rather than expected destination QNH,you answer.."In case of depressurisation sir!"..
He will then think.."Smart arse"... so be prepared for a hard time!
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Old 20th Jun 2017, 18:30   #26 (permalink)
 
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Originally Posted by Chesty Morgan View Post
That depends on type.
Sure, but since we are mainly discussing an Airbus specific subject in this topic...

Anyway, which aircraft chase the altitude in the window when in 'Alt Hold' mode'?

Quote:
Originally Posted by Basil View Post
I really don't know what you're talking about . . . .
Well, you were telling us to adhere to SOP's. To my knowledge there is no SOP that prescribes or prohibits preselecting QNH. Hence my question, which SOP's you want us to adhere to.

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Originally Posted by vilas View Post
Line pilots are supposed to follow SOPs and not devise their own procedures. Creativity in cockpit is fraught with danger. It's not airbus SOP. Besides it is very myopic action. What if QNH changes? If you get in the habit of pre setting you are likely to forget to change that to the new setting.
SOP's do not cater for every single step of operating an aircraft, pilots are left to fill in the voids. Your SOP-centrist view is just as much a risk as a more 'common sense' approach to SOP.

Last edited by PENKO; 20th Jun 2017 at 18:52.
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Old 20th Jun 2017, 20:34   #27 (permalink)
 
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PENKO, as I said: Any captain who fails to follow SOPs (without good reason) is making life difficult for his FO and reducing safety.

I don't know your experience or for whom you fly or if you are, indeed, a professional pilot but, in my experience of mil and several civil airlines, it was normal to have the correct subscale setting for the current part of the flight and we will just have to disagree.
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Old 21st Jun 2017, 06:28   #28 (permalink)
 
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What you consider 'normal' could be an opinion, practical drift, cultural preference, hopefully common sense, but not necessarily SOP.

Anyway, back on topic, our SOP's in one of the largest Airbus 320 operators in the world, actually cater for presetting the QNH in the cruise. For both the main altimeters and the standby altimeter. One of the restrictions: don't do it when you approach a level off because you risk an untimely ALT*

Last edited by PENKO; 21st Jun 2017 at 06:41.
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Old 21st Jun 2017, 13:23   #29 (permalink)
 
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our SOP's in one of the largest Airbus 320 operators in the world, actually cater for presetting the QNH in the cruise
As I said in #16: If it's SOP then that's what you do
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Old 21st Jun 2017, 14:28   #30 (permalink)
 
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Originally Posted by ADFUS View Post
If it's such a bad idea then why does airbus allow to preset the QNH without leaving the STD mode on their new jets?
Sorry felt compelled to intervene in this discussion. The Mode S transponder is completely unrelated to the main or standby altimeter subscales and settings.

It derives information from ADRIU and Air data system but its horses to suggest sub scale setting is a factor in TCAS for momentary finger trouble in Alt Hold mode.
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Old 23rd Jun 2017, 06:21   #31 (permalink)
 
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Originally Posted by Basil View Post
As I said in #16: If it's SOP then that's what you do
Yes and thereby you imply that if something is not covered by SOP you don't do it. Which is inherently false since SOP's don't cover each and every situation. If, like is the case in the thread starter's company, there is no SOP regarding preselecting QNH then at best you can say that this procedure is a grey area, perfectly open to discussion. i.e. you use your judgement.
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Old 23rd Jun 2017, 09:35   #32 (permalink)
 
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Originally Posted by Dogma View Post
...but its horses to suggest sub scale setting is a factor in TCAS for momentary finger trouble in Alt Hold mode.
That is not the necessarily the case. I used to fly a Fokker. In the cruise with STD set, you can (pre)set the altimeter subscale without upsetting the aicraft. But if you press the wrong button (Baro/STD) with ALT hold the aircraft will climb/descend to maintain the altitude associated with the numbers that the aircraft was holding. I now a fly a jungle jet with Mrs. Honeywell's most dreadful avionics (more bugs than rotten meat with worthless but very expensive customer (victim?) support) Change the subscale and the aircraft may pitch or bunt to get to the level that was associated with numbers that were being held. Do that at the wrong time...

But I fully accept not all aircraft will do this.
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