View Full Version : Cathay interview questions--stumped!!
5th Jul 2005, 19:52
Hey ive been all over this site, I have used the search fuction, I have the hotmail account info, and I still cannot find the answer to these three questions. Please help. Im looking for a basic way to explain the fuel usage in the 747 and the A340. The info I have from the hotmail account is great, but lacks clarity in this area. The second is with regards to what are IRS and Omega navigation systems, i cant find anything on either of these two, except for the fact that Omega was discontinued in the US in 1997. Last but not least is with regard to takeoff climb segments. Are the questions tailored to FAA part 25 requirements or to some ICAO standard, and what they with respect to gross and net takeoff performance. Thank You in advance for all the information. This forum rocks, and has been a tremendous help in my preparation for the interview processs.
The below are simplified a bit, but they are not going to want specifics.
CWT and Tanks 1 + 4 for T/O
CWT once flaps up
30 Min after T/O HST transfers to CWT
Once CWT empty, tanks 2 + 3 feed all engines
Reserves transfer to Mains 2 + 3 when a certain level reached
When Qty in 2 or 3 is the same as 1 or 4, "Tank to Engine"
Bit rusty, but I think the order of use is
Aim is to keep the C.G as aft as possible for as long as possible.
Take off Segments.
Jars-Ops is likely the safe bet, but if you are from the US and don't know FAA stuff it may seem a bit odd.
Omega Loran etc. NFI. Can't believe they are still asking that crap.
6th Jul 2005, 02:28
You'll be able to find detailed answers to your questions in the tech form. Also, I found good descriptions of the A340 and 744 fuel systems in the "Airliner Tech" series books. The systems are similar in that they both use the horiz stab for fuel storage, but in the A340, fuel is moved fore and aft to optimize C of G, whereas in the 744, it can only be moved forward. A picture of the 744 fuel system can be found at:
Omega is an obsolete navigation system and reference to it can only be found, it seems, in outdated Cathay interview study guides. I doubt you'd get a question on this and if you did, saying "the system has been obsolete and unapproved for aviation use by ICAO member states since 1997" would surely be a sufficient answer.
On INS and IRS, again, search the Tech forum, or have a look at a basic avionics textbook. A really thorough explanation of IRS can be found at:
On take-off climb segments, I found that the criteria were not significantly different between FARs and JARs, as long as you can find the most current documents.
6th Jul 2005, 03:43
Is the Tech forum mentioned above is the Tech Log in the first few forums?
6th Jul 2005, 03:45
Yes, this one:
In search, just restrict your search terms to this forum.
13th Jul 2005, 22:01
Any brief explanation about 747-400 and A340 Press. and a/c systems as an interviewer would like to hear? (ACM, Freon etc.)
14th Jul 2005, 08:35
Keeping it simple:
With the ACM, hot bleed air from the engines is piped through usually 2 heat exchangers (cooled by RAM air). Then it goes into a Compressor where it is compressed to a high temperature. Then goes through another heat exchanger where it cooled slightly. Then goes through an expansion turbine (connected to the compressor) where the process of expansion will greatly reduce it's temperature. It's now cool enough to go into a mixing box, where it is mixed with either hot bleed air or recirculated cabin air so that it is the correct temperature for going into the cabin.
The type of Q's you might be asked would be:
Where does the air come from for the Air Conditioning ?
How does it cool the air ?
At what point do you think the air is the coolest ?
Freon is slightly different. I don't know on what aircraft they use Freon machines but i thought some smaller turbo props might have them.
A Gas (Freon) is compressed into a pipe, it's temperature increases (as does the pipe), the gas is now allowed to expand where it's temperature drops (as does the pipe). Air that needs to be cooled is blown over the cooled pipe (as a result of the expanding gas inside). The fridge in your kitchen works like this.
27th Jul 2005, 11:28
OMEGA/VLF is a long-range, random-route navigation system based on Very Low Frequency (VLF) transmissions from a small number (8 stations originally, now???) of very powerful land based transmitters, each capable of providing signal coverage at distances as great as 11,000 NMs. It is an enormously complex system in nearly every sense and is somewhat vunerable to atmospheric distortions. I consists of computers and atomic clocks and combines principles of dead reckoning with ground based electronics. It is a very very technical system and therefore most average operators are incapable of using it properly leaving room for gross navigational errors.
The system consists of two separate systems, OMEGA & VLF. Each exists for entirely different reasons. OMEGA for navigation and VLF for communication. (VLF is a very high powered communication system operated by and for the US Navy primarily for direct comm with submarines anywhere around the world with a range of 6000 to 11,000 NMs. VLF signals are an excellent source of navigation, since they are very stable and predictable with worldwide coverage.)
OMEGA is in simple terms ground baesd GPS, consisting of 8 stations located around the world. The signals travel along the earth's surface all the way around the earth, in fact the Omega recieves two sets of signals from each station, one traveling the long way around the world which if not disregarded by the OMEGA reciever will cause one of the many propogation anomolies called "wrong way propogation".
Each of the eight OMEGA stations transmits a series of three freqs. These are always broadcast in the same order, with the same interval(0.2 secs) between each freq, but with a different interval after the last freq and the begining of the new cycle. The complete cycle for each station, including the unique interval between stop and start, lasts exactly 10 seconds and is repeated continiously. The OMEGA reciever can identify each station by it's trasmission pattern, however each station alse transmits a fourth freq for more positive and rapid ident.
OMEGA's advantage over IRS (INS) is that via the ground station signals it regularly computes and updates it's present position, unlike the pure INS/IRS system which is a self contained setup of gyros & accelerometers and no matter how accurate it will drift over time and without updates it will eventually provide erroneous data. These updates for the INS/IRS are provided via GPS, DME, VOR, etc... normally a combination of the above making it full proof. But in the old days (pre-GPS) long-range overwater oceanic flights with no VOR, no DMEs around had to either rely on INS drift accuraccy (very complex system as well but much easier to use than maintain) or OMEGA/VLF with it's regular auto updates providing more accuracy. Omega/VLF was subject to many differrent propogation anomolies which required very high operation proficiency & system operation knowledge to recognize and compensate for.
OMEGA/VLF onboard systems were much cheaper and lighter than comparable INS systems and were much less prone to mechanical breakdowns.
I'm now dizzy having just remembered all that. I'm surprized anyone still asks about this ancient system at interviews, it's not even in use anymore as far as I know.