Instrument Landing System

[grasscutter]

It can often be seen when an aircraft is on final approach the direction line is not in line with the centre line on the runway and as such the aircraft on the screen is shown landing adjacent to the runaway. Why should this be.

[RodBearden]

Hi Grasscutter

This will usually be on older airliners which only have inertial navigation systems and not GPS. This means that their reported position drifts over time.

For example, Usually, Boeing 737-300's show this problem, but 737-800's, with more modern equipment, line up perfectly with the runway.

Hope that helps

Rod

[Andy Frost]

Another reason might be that the ILS is out of service as it is at Manchester at the moment on approach to runway 23R. Instead pilots have to make a VOR/DME approach and have had to do so for a couple of weeks now. It is resulting in some rather interesting approaches as they pass over a mile from touchdown.