Help on B-747 Tech

[FlyBoy4781]

Hey Guys/Gals...

I tried looking in the tech long and couldnt find any anwsers on some 747 questions maybe some of you brillant CX guys and gals can help. :)

1. What is the diff. pressure on the 747?

2. What is the pressurization on the 747 run off of?

3. What is higher? VMCG or VMCA and why???

[Drunknsailor]

Ok, if you are studying for an interview, you are on shaky ground if you have not previously flown the 747. If they ask you stuff that in-depth about an airplane you have not previously flown and you try and pull the wool over their eyes, it will not bode well for you! Furthermore, if you answer the questions correctly and have the misfortune of interviewing with a current 47 guy, he will drive you into the ground. Better study on the conceptual stuff and be honest and say you don't know than try and have a bunch of random facts about an airplane you are not qualified on.

That being said, you should know where fuel is kept in all Cx's airplanes and GENERALLY in what order the fuel is burned, what kind of engines are on each, how much thrust(approximately), and I have heard of people being asked about gross weights. Again though, it is probably better to know APPROXIMATE values rather than exact figures. If you can have a general discussion about CX's airplanes and other heavy jet operations you will come across as a well-read and intelligent individual as opposed to a fact regurgitator.

[FlyBoy4781]

Drunkensailor,

Very good point. I totally agree with you on what your trying to get across. I know Im not a 47 driver ( just a little RJ driver) but I was just trying to find the anwser to some of those questions that were in the Capt X Y Z book. thats all mate.....

[DirectAnywhere]

1. Max certified diff is 9.4 PSI. Various systems regulate it a maximum 8.9 PSI and it's typically kept at 8.6 PSI.

2. Three air conditioning packs consisting of air cycle machines and associated plumbing. Air source is bleed air either from the APU on the ground or engines once they're up and running.

3. Vmca 3 is lower than Vmcg. It's actually well below the stall speed so it's of no practical significance. It's lower primarily because of the fact that Vmcg only allows use of the rudder for control whereas Vmca allows the use of other aerodynamic controls ie. aileron. Vmca2 is higher than Vmcg. Primarily becuse it's certified on 2 engines rather than 3 for Vmcg. Check out "Handling the Big Jets" (standard source) or do a google search on FAR 25 and research the differences in certification requirements.

There are also some good (and not so good!) discussions here:

http://www.pprune.org/forums/archive/index.php/t-136625.html

http://www.pprune.org/forums/showthread.php?t=71279&pp=15

The following site has an interesting discussion on takeoff performance for FAR 25 aircraft. There is at least one typo in this article though.

http://flightcrewtraining.us/_wsn/page2.html

[FlyBoy4781]

Thank you Sir for the info..... :D

[Drunknsailor]

I didn't mean to come down on you that hard. It's just that I've had some colleagues come back with horror stories from CX interviews saying they were asking obscure stuff about the -400. I didn't get anything like that so I can only surmise that they dug their own graves by acting like experts.

One pressurization question though: The -400 has a higher max. differential than the RJ what does that mean in the real world?

Have fun with HTBJ!

[FlyBoy4781]

Drunkin,

Hey no worries. I just really wanna do well on this interview. So I figured, who not study with all means possible. Thank you for your advice and help. I know its a long road to a job, but Im givin it my 100%:)

[FlyBoy4781]

DirectAnywhere,

Thank you for your Tech info.... I got all I need on that subject. Take Care

[FlyingSpanner]

Drunken Sailor, an increased max diff means that the aircraft can fly higher and still maintain an 8000 ft cabin altitude.

FlyingSpanner :ok: