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[oxford blue]

I'll answer Q5. Someone else can pick up the rest.

I have to say that I do wonder why you're posting some of this stuff. It is you who is supposed to do the work to become an airline pilot, not me. I've had my career. I did it by hard work, application, and thirst for knowledge, not by setting other people up!

That said, I'm always pleased when people are interested.

IRS (Inertial Reference Systems) are a development of INS (Inertial Navigation Systems).

IRS is a 1990s technology. INS was a 1965-70 technology. There are 3 main differences. (1) System Integration. (2) Laser Gyros. (3) A virtual platform instead of a real one.

I am assuming you know what an INS is. If you don't, then you really are just using us.

(1) If you were an airline which had bought an INS in 1970, it would have been an add-on extra in your Boeing 707 or Caravelle. A new navaid to supplement your VOR/ADF/DME. Sure, it would have had a set of damn fine gyros, but it wouldn't have replaced your ADI/HSI/radar scanner gyros.

These days, we bring the system designer in early. As INS/IRS needs such a good gyro to make it work, why have tacky old ADI/HSI/radar scanner gyros as well? Take everything off the IRS and save duplication.

(2) Laser gyros are cheaper and more accurate than huge rotating lumps of shaped iron. If you want to know more, enrol on the Oxford course.

(3) It's not necessary to have heavy electrical engineering to keep a platform level. Expensive, well-engineered analogue control systems might please engineers, but they go wrong quite often. Why not, instead, bolt the gyros and the accelerometers to the floor instead of trying to keep them level? You can then sort out the directions in 3 planes by complicated computing. That way, all you get is a lot of little 1s and 0s rushing about in a computer processor which is a virtual model of which way is up, instead of the real thing.

IRS isn't 'better' than GPS. GPS is acually more acurate - most of the time! However, it has a different type of reliability. If you have 2, or even better, 3 IRSs on board and you have a system of cross-checking, as each one is totally independent, it's very unlikely that all of them will be wrong to put you in precisely the same (wrong) place. GPS isn't like that. When it's good, it's very very good. But if it's wrong all of your GPS receivers will be the same amount wrong, so you'll never spot the problem. More importantly, on a bad day, you just might not be able to get a sufficiently reliable GPS signal for the thing to work at all.

And don't forget the bottom line. On a bad day, the US Government might just decide to switch GPS off for political or military reasons. Even though one hopes that that's pretty unlikely, the world is an uncertain place and you can never be sure. However, no-one can switch IRS/FMS off. It is totally self-contained within the aircraft. It depends on no-one.