Iru 767
 

I was reading and it says that you need to align the iru before a flight.
I'm only a ppl but i am interested in flying these some day and i couldn't understand because if they recieve their co-ordinates from gps why do the pilots have to align it. Because i thought gps is automated.

Thanks muchly for your help:D

Inertial reference units are self contained devices that use a system of laser ring gyros to measure displacement of movement over the Earth. They are initialized so that they know where they are starting from. These units usually combine inputs from distance measuring equipment stations on the ground to compute an updated and accurate position where available via a flight management computer.

Global Positioning systems use cross fixes from satellites in synchronized operation above the Earth to establish a relative distance fix position. They naturally require input from 4 or more satellites to be effective.

You are confusing two different systems.

This will help with GPS
This will help with IRS
This will help with RLG's
This will help with basic research

thanks for your help and the links.
So i am guessing gps isn't available on the 767 or it is unreliable?

I've just read it says an accuracy greater than one metre has been accompished after saying the accuracy was 10-20 metres.
:D HAHAHA that last link was funny good job i had finished my dinner
Phil

GPS is used on some 767s
 

We have a 767 fleet that is about 50% FMS with GPS & IRS, and the other 50% FMS with IRS only.

On the jets with GPS, we align the IRSs (using the FMS) utilizing the more accurate GPS position.

On the jets without GPS, we input stored gate coordinates, or if unavailable, manual Lat/Long entries.

Regardless of where the coordinates info comes from, the other pilot is required to verify their accuracy using a separate source document.

philip - you need to do more 'reading' - suggestion (4) by 'Bealzebub' was not meant purely as a joke! Quote 'You are confusing two different systems'.

AFAIK, in the UK, GPS is not certified as a 'sole means of navigation'. This means that even with the best GPS in the world, you need the INS system to fly legally. Without it there are severe restrictions on what you can do. That is why it is 'aligned' before departure, indeed using the GPS position to do so (after confirming it is correct). Yes, GPS is accurate to a fine degree (assuming, of course, the signals are not interfered with as with the US military GPS system). The INS has at its heart an IRS system which gives attitude information amongst other things, which GPS cannot.

All these definitions are available on Google' and the 'Tech Log' forum has some useful links at the top.

Sorry yeah i should have checked if there was info out there first but thanks for the feedback anyway.:O

BOAC,
In principle, the CAA do allow GPS as sole means enroute navigation, although there is still a requirement to have NAV and DME receivers for approaches. In practice, you also rely on the traditional nav sources as the backup (and cross-check!!).
In order for it to be absolutely sole means (for oceanic ops) you have to do a pre flight check that RAIM will be available throughout the flight. Because there are rare occasions when the computer tells you this is not the case, in practice it is a bit of a nuisance. However, since the vast majority of aircraft that routinely fly oceanic routes have iru's anyway it's not normally a problem.
As an interesting aside, contrary to popular belief they also in principle allow GPS approaches, but since no-one has paid for any of the approaches in the UK to be recertified as overlays (let alone any new standalone ones) there are no published approaches to do.

But I do like the independence of IRS navigation!:ok:

So gps's can go wrong then so that's why we still use irs?
Thanks for all your responses.
:D

Thanks BJJ - did not know that.