FAO Gabriel The Aeroengineer

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FAO Gabriel The Aeroengineer

Postby flyboy2548m » Mon Jul 24, 2017 1:45 am

You know, Gabe, EVERY time I try to think you actually might know something, you go and ask a question so asinine, I damn near feel like crying.

How is it that an aerodynamicist of your immense caliber doesn't know this?
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Re: FAO Gabriel The Aeroengineer

Postby Gabriel » Mon Jul 24, 2017 8:39 am

Thanks!

Does the HI ALT LANDING pb-sw also increases the cabin altitude that will trigger the high cabin altitude warning?
Would the pilots be required to use the O2 masks, since they would be operating at a cabin altitude above 10000ft? (until somewhere into the climb for departures, as the cabin altitude descends from the field elevation to 8000ft, and since somewhere during the descent/approach for arrivals, as the cabin altitude climbs from 8000ft to the field elevation)

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Re: FAO Gabriel The Aeroengineer

Postby 3WE » Mon Jul 24, 2017 5:49 pm

Just being a smart-donkey (or a smart squid)

But shouldn't the wording be that the masks drop if the pressure goes BELOW 14,000 feet?

Or if you want to use the word 'exceed'...then if the cabin altitude exceeds 14,000 feet (16K when the switch is on).

:ugeek: :twisted: :lol: 8-)
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Re: FAO Gabriel The Aeroengineer

Postby Gabriel » Mon Jul 24, 2017 9:54 pm

Just being a smart-donkey (or a smart squid)

But shouldn't the wording be that the masks drop if the pressure goes BELOW 14,000 feet?

Or if you want to use the word 'exceed'...then if the cabin altitude exceeds 14,000 feet (16K when the switch is on).

:ugeek: :twisted: :lol: 8-)
You are absolutely correct. Maybe it's a bad translation from a French crackerbox manual.

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Re: FAO Gabriel The Aeroengineer

Postby flyboy2548m » Mon Jul 24, 2017 11:14 pm

Thanks!

Does the HI ALT LANDING pb-sw also increases the cabin altitude that will trigger the high cabin altitude warning?
Would the pilots be required to use the O2 masks, since they would be operating at a cabin altitude above 10000ft? (until somewhere into the climb for departures, as the cabin altitude descends from the field elevation to 8000ft, and since somewhere during the descent/approach for arrivals, as the cabin altitude climbs from 8000ft to the field elevation)
Now you're just playing with me. Not interested, sorry.
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Re: FAO Gabriel The Aeroengineer

Postby Gabriel » Tue Jul 25, 2017 3:25 pm

Thanks!

Does the HI ALT LANDING pb-sw also increases the cabin altitude that will trigger the high cabin altitude warning?
Would the pilots be required to use the O2 masks, since they would be operating at a cabin altitude above 10000ft? (until somewhere into the climb for departures, as the cabin altitude descends from the field elevation to 8000ft, and since somewhere during the descent/approach for arrivals, as the cabin altitude climbs from 8000ft to the field elevation)
Now you're just playing with me. Not interested, sorry.
I am not. These are honest questions for which I guess (based on reasoning) that the answer would be "yes" but that I don't know for fact.

I was surprised that the part of the manual that you shared says what the high alt landing switch does with the cabin masks but not with the high cabin altitude warning. Perhaps there are other explanations. Perhaps when you select a field altitude, the high altitude warning will be inhibited unless the cabin altitude is above some margin above the selected field altitude. That would make sense on one hand, but on the other hand you would lose the "reminder" for the pilots to don their masks for the time that the cabin altitude goes from say 10000ft to 14000ft (field elevation). Because I suppose (but don't know for fact) that the pilots will need to use supplemental O2 during this brief part of the operation.

If you want to answer me and educate me, you are welcome and much appreciated, but I am not playing with you and I will not enter in the futile arguments of the past.

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Re: FAO Gabriel The Aeroengineer

Postby flyboy2548m » Tue Jul 25, 2017 5:00 pm

I am not. These are honest questions for which I guess (based on reasoning) that the answer would be "yes" but that I don't know for fact.

I was surprised that the part of the manual that you shared says what the high alt landing switch does with the cabin masks but not with the high cabin altitude warning. Perhaps there are other explanations. Perhaps when you select a field altitude, the high altitude warning will be inhibited unless the cabin altitude is above some margin above the selected field altitude. That would make sense on one hand, but on the other hand you would lose the "reminder" for the pilots to don their masks for the time that the cabin altitude goes from say 10000ft to 14000ft (field elevation). Because I suppose (but don't know for fact) that the pilots will need to use supplemental O2 during this brief part of the operation.

If you want to answer me and educate me, you are welcome and much appreciated, but I am not playing with you and I will not enter in the futile arguments of the past.
For the record, I don't believe you, but let's set that aside for the moment. As I'm sure you're aware, I'm not real big on spoon-feeding, particularly when engaged in conversation with a specialist of your caliber, so, instead, I'll give you some homework.

It seems you'd do well to research transport-category aircraft pressurization systems in general, pay special attention to the concept of pre-pressurization (that's a Boeing term, but the idea applies across the board). You seem a little confused on what happens and when.

You also seem real hung-up on the O2 mask issue. So, in your research, see if you can figure out how long it would take for the cabin to descend back to 8,000 (or at least below 10,000). I think you'll find it's a non-factor.

Lastly, you might want to research how FWCs work and which warning are inhibited and when.

And yes, the above panel is for a 320-series aircraft.
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Re: FAO Gabriel The Aeroengineer

Postby 3WE » Tue Jul 25, 2017 6:56 pm

***You seem a little confused on what happens and when.***
Whenever whatever happens, I am sure it is somewhat related to a type-specific checklist.
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Re: FAO Gabriel The Aeroengineer

Postby Gabriel » Wed Jul 26, 2017 2:42 am

For the record, I don't believe you, but let's set that aside for the moment. As I'm sure you're aware, I'm not real big on spoon-feeding, particularly when engaged in conversation with a specialist of your caliber, so, instead, I'll give you some homework.

It seems you'd do well to research transport-category aircraft pressurization systems in general, pay special attention to the concept of pre-pressurization (that's a Boeing term, but the idea applies across the board). You seem a little confused on what happens and when.

You also seem real hung-up on the O2 mask issue. So, in your research, see if you can figure out how long it would take for the cabin to descend back to 8,000 (or at least below 10,000). I think you'll find it's a non-factor.

Lastly, you might want to research how FWCs work and which warning are inhibited and when.

And yes, the above panel is for a 320-series aircraft.
Thank you very much for the cues. I will try to see what I can find online and will come back here with my findings.
The first thing that I had to research was what's FWC, because I had no idea. It seems to be a quite common acronym, but I found one which seems to be a good match for the context of this conversation: Flight Warning Computer (I didn't even know that such a thing existed).

I am sorry that you don't believe me. I don't know why you think that I think that I am a specialist of such a caliber in everything aviation. As anybody else, I know some things better than others (and airliners systems is not a strong one), I don't know everything there is to know of any specific subject, there are things that I don't even know that I don't know (the subject of this thread was one of them, I had never reflected on this before so I wasn't even aware that it existed), there things that I think I know but I am mistaken, and there are things that I am very confident of my knowledge (which still doesn't mean that I cannot be mistaken) and for which I have a stronger position. Now, you take the things that I argued vehemently (what I did because on those I think I had a strong position and good knowledge) and take that as if that was my behavior in everything, and that's not the case. I know that there are things I don't know well and when I find them interesting I ask or try to find information about them, and I know that I am mistaken at times with things that I thought I knew, and I LOVE to be corrected (with explanations, not by imposition of credentials) because I don't want to have "wrong knowledge". You can see that I respond in the same way. I never said "this is like this because I say so and I am a hell better aeroengineer". (I did say that I am a hell better aeroengineer, but not that that was the reason why I was right, I gave a full explanation on the subject, that if I remember correctly was about stalls).

So that's it, that's me. You still can say that you don't believe me, and well, I don't like it but I am not willing to fight it either.

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Re: FAO Gabriel The Aeroengineer

Postby Gabriel » Thu Jul 27, 2017 4:40 pm

So here is the results of my internet research (partially successful I would say)
It seems you'd do well to research transport-category aircraft pressurization systems in general, pay special attention to the concept of pre-pressurization (that's a Boeing term, but the idea applies across the board). You seem a little confused on what happens and when.
That was very interesting, thank you. I found only few references and all of them where in internet forums, but one of them looked particularly reliable since it said that it wa based on Boeing's manuals.
So it seems that in some aircraft types the plane starts to pre-pressurize when TLA exceeds a certain somehow-high setting, that would be, when the pilots advance the thrust levers for take-off. So the cabin altitude increases at a rate of about 300/500 ft/minutes during the take-off (and the cabin descends below the plane's and field elevation) but this is limited to just about 200ft until the plane lift-off as detected by the WOW switches (according to some comments that small pressure differential would not even prevent the opening of the doors in an emergency evacuation). A similar pre-pressurization happens shortly before the landing, where the plane would pre-pressurize so it lands with a cabin altitude about 200 ft below the field elevation, and this accumulated pressure is released after touchdown at a rate of 300/500 fpm.
So 2 takeways related to the discussion in the "other" forum:
- Operating in a field at 13 or 14K ft, this pre-pressurization is very small to be of any significant impact on the cabin altitude for the sake of high cabin altitude warning, O2 masks deployment (that Flyboy already explained), or the need of supplemental O2 for the pilots.
- On departure, this pre-pressurization starts to happen only at the beginning of the take-off roll (and gradually). In my research I also found that the outflow valve remains open with the airplane on ground until this pre-pressurization happens, so I don't find any evidence that 3BS's accounts of the airplane starting to pressurize as soon as the doors are closed, as measured by his Mark IV carbon-based pressure sensors, is anything more than an illusion.
You also seem real hung-up on the O2 mask issue. So, in your research, see if you can figure out how long it would take for the cabin to descend back to 8,000 (or at least below 10,000). I think you'll find it's a non-factor.
I admit that in this case I was thinking more in Evan's black/white legal procedural prescriptions terms rather than in the practical effects.
I guess that the procedures say that the pilot will don the O2 masks whenever the cabin altitude is above 10000 ft without many "fuzzy" indications regarding how much or how long above 10000 ft. Except that there might be a special prescription for high-altitude fields ops. I just don't know and I couldn't find anything in the internet.
On more practical terms... I found that cabin VS seem to be restricted to 750 fpm in normal circumstances, but is typically lower than that. So let's take a sort of worse-case and say that the field is at 14K ft and the cabin descends at 500 fpm, it would take 8 minutes to reach 10K ft.
The time of useful consciousness is "30 minutes or more" at 15000 ft, and it will be infinite for most people at 15000 ft and even more at 14000 ft. However, reaction times, mistakes likelihood, and judgement, all start to be impacted well below those altitudes (even if only so much and not nearly enough to render you unusefully conscious). In the case of the departure, you have been exposed to 14000ft for maybe a day or two. And you will be starting the engines and running many critical tasks and checklist well before the cabin altitude starts to descends. So maybe it would not be a bad idea to go on O2 as soon as the pilots get into their seats and start with all these critical flight preparation tasks and checklists.
Again, even if it is not necessary from a practical point of view, that doesn't mean that it is not mandatory as per the procedures (again, I don't know).
Lastly, you might want to research how FWCs work and which warning are inhibited and when.
For this one, unfortunately I didn't find any useful information in my internet research. I would appreciate you shedding some light on this, if you will.

But in any case, thanks for the hints. The research was very interesting and I did learn some things that I had no idea about (especially regarding the pre-pressurization).
Last edited by Gabriel on Thu Jul 27, 2017 4:44 pm, edited 1 time in total.

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Re: FAO Gabriel The Aeroengineer

Postby Gabriel » Thu Jul 27, 2017 4:43 pm

Duplicated

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Re: FAO Gabriel The Aeroengineer

Postby flyboy2548m » Fri Jul 28, 2017 2:55 pm

That was very interesting, thank you. I found only few references and all of them where in internet forums, but one of them looked particularly reliable since it said that it wa based on Boeing's manuals.
Well, as long as it looked reliable because of what it said, certainly all is well in the world.
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Re: FAO Gabriel The Aeroengineer

Postby Gabriel » Fri Jul 28, 2017 4:06 pm

That was very interesting, thank you. I found only few references and all of them where in internet forums, but one of them looked particularly reliable since it said that it wa based on Boeing's manuals.
Well, as long as it looked reliable because of what it said, certainly all is well in the world.
Well, not only that. I read through it and used my [finite] knowledge, [non-mistake-proof] reasoning, [fallible] intuition and [imperfect] common sense to judge it reliable. Now, I am 100% sure it is reliable? I am not. That's why I said "looked reliable".
As a counter example, I have never given any information to any email requesting it just because it claimed to be from my trusted bank.

Judge by yourself:
https://aviation.stackexchange.com/ques ... the-ground

This one also claims to cite an AMM:
http://www.pprune.org/tech-log/545406-b ... round.html

And, in any event, when I asked you a question, you gave me homework, and I did the best I could with the resources I had. Fell free to (and please do) correct any mistakes in it, or to provide additional information.

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Re: FAO Gabriel The Aeroengineer

Postby flyboy2548m » Sat Jul 29, 2017 3:08 pm

It sounds to me like the next thing you might want to research is cockpit oxygen systems, particularly how long the O2 supply will last if it's being used for all operations above 10K or whatever (engine starting, decision making and all). Maybe then you'll rethink the whole "not a bad idea" etc, O the Beacon and Candle of Argentine Aerodynamics.
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Re: FAO Gabriel The Aeroengineer

Postby Gabriel » Sun Jul 30, 2017 4:32 pm

It sounds to me like the next thing you might want to research is cockpit oxygen systems, particularly how long the O2 supply will last if it's being used for all operations above 10K or whatever (engine starting, decision making and all). Maybe then you'll rethink the whole "not a bad idea" etc, O the Beacon and Candle of Argentine Aerodynamics.
Well, it seems that a full bottle of O2 will last about 30 minutes at 100% O2 for 4 crew members. That would be about 1 hour for 2 crew members I guess. Now, that's 100% O2. Select N and you will be breathing a mix of O2 from the bottle and cabin air, with the amount of O2 regulated automatically in function of the cabin altitude. I guess that at 14000 ft of cabin altitude, the O2 will be much much less than 100%, and hence the duration of the bottle will be much much more.

In any event, that's not really relevant. IF pilots are REQUIRED to use O2, then they are required. If the bottle is not big enough, then put a bigger one. In the same way that special high-speed tires are sometimes installed in airplanes operating at high altitude airports, you could install a bigger or additional bottle, or provide some other source of supplemental O2 independent of the normal one. Or get an exception from the aviation authorities. In some way or another, you need to comply with the regulations.

I found this:
PART 121—OPERATING REQUIREMENTS: DOMESTIC, FLAG, AND SUPPLEMENTAL OPERATIONS
Subpart K—Instrument and Equipment Requirements
§121.329 Supplemental oxygen for sustenance: Turbine engine powered airplanes.

(b) Crewmembers. Each certificate holder shall provide a supply of oxygen for crewmembers in accordance with the following:

(1) At cabin pressure altitudes above 10,000 feet, up to and including 12,000 feet, oxygen must be provided for and used by each member of the flight crew on flight deck duty and must be provided for other crewmembers for that part of the flight at those altitudes that is of more than 30 minutes duration.

(2) At cabin pressure altitudes above 12,000 feet, oxygen must be provided for, and used by, each member of the flight crew on flight deck duty, and must be provided for other crewmembers during the entire flight at those altitudes.
Depending on the interpretation of "flight" and how you count the 30 minutes, it may be argued that the flight crew is required to use supplemental O2 since much earlier than lift-off (engine start? start performing flight crew duties?) until the cabin altitude reaches 10000 ft.

Yet, even with the most benign and naif interpretation, unless some other regulation specifies something different for high altitude airports, that means that flight crew is required to use supplemental O2 since lift-off at least for the few minutes it takes the cabin to go from say 14000 ft to 12000 ft.

Of course, you do know things that I don't, so please shed some more light on the subject.

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Re: FAO Gabriel The Aeroengineer

Postby flyboy2548m » Mon Aug 14, 2017 8:24 pm


Of course, you do know things that I don't, so please shed some more light on the subject.
Nah, you got your hands full with all that traffic at MIA, so I'll leave you be.
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Re: FAO Gabriel The Aeroengineer

Postby 3WE » Tue Aug 15, 2017 8:43 pm


Of course, you do know things that I don't, so please shed some more light on the subject.
Nah, you got your hands full with all that traffic at MIA, so I'll leave you be.
C'mon man...he was joking.

Bobby inferred that the airport was operating to the East, so a damn amateur landing on 30, against the traffic seems a bit unadvisable.
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Re: FAO Gabriel The Aeroengineer

Postby flyboy2548m » Wed Aug 16, 2017 11:05 pm

C'mon man...he was joking.

Bobby inferred that the airport was operating to the East, so a damn amateur landing on 30, against the traffic seems a bit unadvisable.
It's a controlled airport, they'll work him in.
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Re: FAO Gabriel The Aeroengineer

Postby 3WE » Thu Aug 17, 2017 1:12 am

C'mon man...he was joking.

Bobby inferred that the airport was operating to the East, so a damn amateur landing on 30, against the traffic seems a bit unadvisable.
It's a controlled airport, they'll work him in.
Hmmm...maybe vector him around a while until there's a traffic lull and he can get the feel of Bobby's handfuls of yoke and thrust levers. (I concede that 4 levers does use up most of a typical human hand)
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Re: FAO Gabriel The Aeroengineer

Postby Gabriel » Thu Aug 17, 2017 4:53 am

Or, I can declare emergency and announce my intentions, and let them move all other planes away from my path.

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Re: FAO Gabriel The Aeroengineer

Postby 3WE » Thu Aug 17, 2017 4:19 pm

Or, I can declare emergency and announce my intentions, and let them move all other planes away from my path.
In this forum of slightly higher understanding, I want to confess that I am conflicted.

I was definitely overly-bold in my confidence that I might be able to land a 'real' 747 simulator using robust speeds and attitudes and runways and visual approach slope tools and Mark IV, low-silicon, alignment, motion-analysis and prediction systems...and close (very close) attention to all the other related stuff....

Still, I recall your landing in a 'real' 737 simulator...most encouraging.

While it's just MSFS- I find it scary that my 'needed final approach length' vs. size if airplane closely matches Bobby's braggin' figures....that and the loose recreation of Delta 191 that so often puts me on the ground a bit short of 17C
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Re: FAO Gabriel The Aeroengineer

Postby Not_Karl » Sat Aug 19, 2017 9:45 pm

Or, I can declare emergency and announce my intentions, and let them move all other planes away from my path.
I would say that a non-commercial, Not_trained/certified on type pilot trying to land a very very very big simulated plane is a pretty good reason to declare an emergency :mrgreen: .
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Re: FAO Gabriel The Aeroengineer

Postby Gabriel » Sat Aug 19, 2017 11:59 pm

I would say that a non-commercial, Not_trained/certified on type, no multi rating, no complex rating,, not current for any flight activity, not holding an american licence while operating an N plane in USA, medical expired, last-hour-logged 18-years-ago, pilot trying to land a very very very big simulated plane is a pretty good reason to declare an emergency :mrgreen: .
Fixed.

But I do have my share of 747 experience in MSFS.


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