Hi,
Although the ILS uses the same instruments and nav equipment as the VOR on the flight deck, the equipment on the ground is completely different.
Put simply:
The equipment uses a couple of localizer beams on different frequencies which overlap one another. The NAV equipment in the aeroplane uses those beams to determine whether the airplane is in relation to the centreline by interpoling the two beams and then outputting the result to the OBS instrument on the flight deck.
Thus, in effect the ILS Localizer only sends out a signal on one course only, ie 123 degrees or 051 degrees, or any one of the 360 degrees possible. Thus if your OBS inbound course on the instrument in the flight deck is set wrong this will NOT matter to the NAV equipment as it disregards the OBS setting.
The ILS Localizer transmits on the lower band of frequencies that cover the ILS and VOR stations. Ie, 110.70 being an ILS frequency and 117.45 being a VOR frequency. So the NAV equipment knows what sort of equipment to expect...
The Glideslope transmits on a seperate frequency but is automatically tuned into the NAV equipment onboard the aeroplane when the appropriate Localizer frequency is dialled in.
The Glideslope itself also has two "beams" sent from a seperate transmitter to the side of the runway and abeam the touchdown of the touch down markers on the runway. The reason for for so far down the runway is to give the pilot enough clearance over the fence.
The NAV box in the aeroplane works out from these two beams (again varying frequencies) as to where the aeroplane is located on the glideslope and then transmits this through to the instrument display.
Normal Glideslopes are at a 3 degree angle. But they do vary, ie Exeter has one at 3.5 degrees. At 60 knots groundspeed this could give you a convenient 300' per minute descent rate.
The reason why you could have had "reverse" sensing of the ILS is that you could have been flying a back course... ie an ILS beam for the opposite runway which one can use for an approach to the other runway. This, however doesn't give you a glideslope.
If you want all of the technical information such as frequencies used etc then let me know and I'll provide it.
One of the best ways to fly an ILS is to work out an inbound heading taking into account the wind. So say you worked out you need a 10 degree correction to the left and the inbound course is 050 degrees, you would initially intercept 040 and see if the ILS Localizer needle moved. If it doesn't then good you're on the centreline but if it does turn left or right (depending) two degrees or so to see if that brings the ILS back into the centre. If it does then either ammend your original correction heading (known at the reference heading) or keep it the same (ie 040). Remember the localiser gets very sensitive near the runway. Use a max of 5 degrees correction at say 10 miles out but near the runway use one or two degrees at any one time maximum.
The glideslope is easily maintained by working out your groundspeed (IAS taking into account the wind) roughly and use the following formula: (Groundspeed / 2) * 10 - this will give you the approximate decent rate in feet per minute that you can obtain on your VSI... if the decent rate isn't enough or is too much then change it by 50 feet per minute or so... the glideslope is very sensitive...
Just a quick note that the instrument in the flight deck is 10 degrees wide either side of the centreline using a VOR but the same instrument using the ILS is only 2.5 degrees wide either side of the centrline.
I'm sure an IR instructor would give you a better explanation for flying ILSs than myself though.
Best wishes,
Charlie Zulu.