Navigation Services
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Ground-Based Navigation Group - Instrument Landing System Description
The FAA continues to support (ground based) ILS and will continue to procure and deploy new and replacement ILS for the foreseeable future. It is expected that ILS (ground based) will be eventually replaced with some type of GPS system in the future (see WAAS and LAAS). Presently the FAA has a contract with Thales, ATM to procure the Mark 20A ILS on a requirements contract. Since March 2000 until March 2004 approximately 150 ILS systems have been acquired on this contract.
In a similar manner as the localizer (just turned 90 degrees on axis), the glide slope sends two frequencies that aircraft instruments determine as above or below the desired glideslope. This is approximately 3 degrees to the horizon which give the aircraft a decent of approximately 500 feet per minute. For an ILS approach there are several components required. The Mark 20A ILS is the electronic and antenna component. You also need a runway (with proper lighting and markings) and approach lighting. Other components may be required such as RVR (Runway Visual Range) and Marker Beacons or LPDME. Note on the diagram the more precise the approach is (lower weather minimums) the more ground and airborne equipment may be required. Acquisition Lead:
Implementation Lead:
Contracting Officer: Bill Keller |
The ILS has been the mainstay of landing aids for well over 50 years. The modernized versions used by the FAA provide aircraft with precision vertical and horizontal navigation guidance information during approach and landing. Associated Marker Beacons and/or Low Power Distance Measuring Equipment (LPDME) identify distance to the runway. The attractiveness of ILS lies in the economy of its avionics costs and its wide international acceptance. Technology advances over the years have yielded great improvements in accuracy, dependability, and maintainability. 
The localizer generates and radiates signals to provide final approach azimuth navigation information to landing aircraft. The antenna sends 90-HZ and 150-HZ signals that the aircraft instruments determine as left and right of the centerline. The aircraft interprets the signal and displays them on the cockpit indicator guiding the pilot until the runway is in sight.
