Aircraft Landing

What is an Instrument Landing System?

An Instrument Landing System is used by a pilot in bad weather to bring down an aircraft in perfect line with an airport’s runway. Two radio beams are sent out by a ground transmitter. The “localizer” is a narrow, upright beam which positions the aircraft in line with the runway. The “glide path” is a thin, flat beam which gives the aircraft a perfectly angled approach path to the end of the runway.

In the case of large, busy airports such as London’s Heathrow, a pilot is in close contact with Air Traffic Control on his approach to the airport for, at peak periods, aircraft can be landing at 45 second intervals.

The ground control operator tells him to “lock on”, a phrase used to tell the pilot to switch on his Instrument Landing System. The pilot informs Control that he is “established”, which means that he has locked on to the two radio beams and is keeping them crossed. The point at which the beams intersect is the spot on the runway where the aircraft must land.