Universal Instrument Landing System (ILS) interlock controller with remoting capability

Abstract

Instrument Landing Systems (ILS) provide vertical and lateral guidance to landing aircraft. The lateral guidance aligns the aircraft horizontally with the extended centerline of the runway while the vertical guidance ensures the proper descent angle for landing. This allows an aircraft to make a landing at an airport that cannot be seen from higher altitudes due to weather, clouds, and/or poor visibility.

The approach path provided by the ILS also ensures an obstacle free corridor. The ILS utilizes ground based electronics and an aircraft receiver. The ground based electronics radiates an amplitude modulated VHF signal through an antenna array. The combined signal in space has different modulation based upon its orientation to the antenna array. The aircraft receiver uses this signal to determine its alignment.

Due to safety requirements, Federal Aviation Administration (FAA) Orders, and International Civil Aviation Organization (ICAO) Standards, an ILS must use an interlock system to prevent more than one ILS from radiating opposite approaches to the same runway or when operation of more than one ILS causes an interference problem with the signal in space reception of the desired ILS signal. This interlock system interfaces more than one ILS and must be controlled by Air Traffic personnel.

Since there is not a common specification for controlling an ILS, individual manufactures are free to use different methods for interlocking their system. The Federal government buys ILSs from competitive bidding. The result is different vender equipment ends up at various airports causing unique interlock designs. Furthermore, until recently, interlocked ILSs were not remoted off airport. Therefore, a universal ILS interlock with remoting capability is needed.