Cabin Pressure Differential: ATPL Exam Question

[Tee]

Can anyone confirm the correct answer to this ATPL Aircraft General Knowledge question?

Normal cabin pressure differential is:-

a. 3-5 psi
b. 18 psi
c. 7-9 psi
d. 12-15 psi

Thanks in advance!

[Siddique]

For say B747 or other public transport type a/c 7 - 9 pdi diff.

[sabenapilot]

answer c :cool:

[stevevanda]

Answer C for sure! :cool:

[ 29 November 2001: Message edited by: Stephen Wood ]

[moggie]

7-9 on both VC10 and HS125

[Shore Guy]

7-9 PSID is about right for transport aircraft. The 51000 foot Lears, etc. have PSID's above 10.0.
The best illustration I have heard to describe the forces involved is aircraft pressure vessels is as follows: The folks who design nuclear weapons consider the ring of destruction for (non-hardened) structures to be the .5 PSID overpressure ring surrounding the blast. We are running with differentials up to 20X that in our aircraft. That is why big people/things can go through small holes with a rapid D.

[JB007]

C is a defin.
This was in the Oxford feedback I managed to get hold of!

[twistedenginestarter]

This is how you would guess the answer.

Surface level is 14 psi. Assume 41000 feet (normal ceiling) is near to zero. The pressure drops to half around 10000 feet ie 7 psi.

Cabin altitude is typically 8000 feet so between 14 psi and 7 psi - let's guess 9 psi. This gives you (0 -9 ) as a maximum which rules out a couple of the options. I think it also rules out the low option as being too far from 9.

Ergo one answer left.

[Gedifroggy]

I confirm that cabin pressure altitude must (I repeat must) be kept at /or below 8000ft (This is also an ATPL question), and that the ceiling for most of A/C is around 40 000ft.So as stated in the previous reply typical diff pressure are around 7/9 psi

[sabenapilot]

This is BASIC knowledge for an airline pilot guys!

max cabin pressu: 7 to 9 psi
max ceiling: FL350 to FL 410
max cabin alt: 8000ft
normal rate of cabin climb: 500 to 600fpm
normal rate of cabin descent: 300fpm
etc. etc.

It's just one of those things that are the same on all planes. Maybe these numbers are not as well known, but still they are very important if you want to keep your pax (and yourself) alive up there.


Now, if I'd ask you what would be a typical N1 settng on a normal take off,
a: 25%
b: 60%
c: 90%
d: 105%
what would be your answer? Do you think this is a difficult question? Then what's the problem with this pressurisation question?

[sabenapilot]

Ok,
so how many commercial planes do you know of with a cabin altitude of 4,000ft, a cabin differential pressure of 13psi, a service ceiling of 60,000ft and a cabin rate of climb of 100fpm?
:eek:

[jtr]

tolipanebas, the guy is asking a genuine question. Yes he/she may be sitting his ATPL, but he/she may never have been in the pointy end of an 8.6psi can, let alone sat there staring at the cabin diff. dial for hours on end. Try asking 10 ATPL holder who have never been out of a light piston what the typical operating pressure of a hydraulic system is. Should we throw stones at those who don't know the answer?

Wind it in a notch son, not every one can be as good as you.

[wheelchock]

tolipanebas,

Regarding your question, de-rated or rated?


:D

[Bellerophon]

BIK_116.8

-.-. --- ..- .-.. -.. -. - .- --. .-. . .
-- --- .-. .

..-. --- .-. .. -. ... - .- -. -.-. .
--- -. -- -.-- .- .. .-. -.-. .-. .- ..-. -

-- .- -..- -.. .. ..-. ..-.
.---- .---- .--. --- .. -. - --... .--. ... ..

-- .- -..- .- .-.. -
..-. .-.. -.... ----- -----

.-. . --. .- .-. -.. ...
-... . .-.. .-.. . .-. --- .--. .... --- -.

:D :D

:( Ooops

[ 07 December 2001: Message edited by: Bellerophon ]

[sabenapilot]

I must admit that most of the knowlegde of an APTL pilot comes from staring at those instruments for hours....

:)

[sabenapilot]

Bellerophon,
what plane do you fly then?
Certainly not an airliner...

BTW, you forgot the "O" in NOT on the first line of your morse message...
:)

[jtr]

All right, I'll bite tol., how much of your ATPL knowledge do you use in day to day ops., and how much do you rely on experience gained post ATPL?

For me I'd say it's about a 5/95 ratio

Holding an ATPL doesn't make you an airline pilot, does it???

[sabenapilot]

Hi Guys-

It's not my view that's blinkered, it's the view of those ATPL examiners. Apparently they are the ones only considering Airbus and Boeing when making this kind of 'general' ATPL exam questions.

Please don't blaim me for this blunt generalization, I just wanted to give you the answer that is the only correct one on the exam + the basic idea (logic?) behind it.

Please don't work out your frustration about this kind of questions on me, simply because I managed to give you the correct answer off-hand. As said before, I just happen to have the 'luck' to be able to stare at instuments of planes which are considered as standard, whereas several colleagues of mine (flying Falcon or Gulfstream) see that their equally nice planes (and their operating values) are totally ignored.

[Bellerophon]

tolipanebas

Only two mistakes in your reply to me! :D

Firstly, I didn't miss out an "O", but I couldn't insert an apostrophe in Morse!

If English is not your native language; and I suspect from your name this may be the case; please forgive me for mentioning this. I really don't mean to criticise, as your ability with foreign languages undoubtedly greatly exceeds mine!

Secondly, it is very much an airliner that I fly, as several people on this forum could tell you. Tickets are readily available on it should you wish to fly LHR-JFK-LHR in a hurry. Enough of a hint? ;)

The point BIK_116.8 and I were trying to make is that one should be very careful when making emphatic statements such as:

"It's just one of those things that are the same on all planes."

Someone always comes along and proves you wrong!

Finally, another assumption from your name, if you are job hunting, I wish you good luck and hope that all goes well for you and you find another position soon.

Regards

Bellerophon

[sabenapilot]

Hi there,

No offence's taken!

Anyway, I think you can agree your plane is not really a standard plane like mine. :o
If we have to take this kind of planes into account when talking about commercial airliners, then there sure wouldn't be much general things around...

Anyway,
Is it me, or is there something wrong is this line too? (D = T)
-- .- -..- .- -.. -

As to my job,
I have found a new one with AirLib in France a few months ago (I saw the problems coming you know...). Very cool I must say, although I have done only 2 combinations so far. Did you know we even go all around the world? Paris -> Los Angeles -> Tahiti -> Paris for instance!!!! :eek:

[sabenapilot]

sorry, I ment to say D = L iso T...

Should stick to morse after all :)