Beam Approach Beacon System
Encyclopedia
A blind approach beacon system or beam approach beacon system (BABS) is an automatic radar
landing system developed in the early 1940s.
It is a responder (or transponder
) mounted in a Hillman
van
and placed at the end of the runway
. In some cases fixed sites were installed and by the mid-1950s Standard 9 vans were in use. It was interrogated by a Rebecca
unit mounted in an aircraft
. It responded by transmitting dot
s on one side of the runway and dash
es on the other. The strength of the reception in the aircraft depended on the aircraft's position relative to the centre line of the runway. The aircraft's equipment could then determine its position relative to these dots and dashes.
This is an early version of the localiser from the more modern instrument landing system
(ILS). The localiser uses two tones (90 and 150Hz
) modulated on a carrier (108-111.975 MHz) and transmitted on a wide aperture antenna array, this can be seen at almost all airports at the end of the runway. The strengths of which (or Difference in Depth of Modulation) are detected by electronics in the aircraft and present the pilot with an indication to fly left or right and indeed up or down with a co-located glidepath (328.6 to 335.4 MHz) equipment. See instrument landing system
for further details.
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
landing system developed in the early 1940s.
It is a responder (or transponder
Transponder
In telecommunication, the term transponder has the following meanings:...
) mounted in a Hillman
Hillman
Hillman is a British automobile marque created by the Hillman Motor Car Company, founded in 1907. The company was based in Ryton-on-Dunsmore, near Coventry, England. Before 1907 the company had built bicycles...
van
Van
A van is a kind of vehicle used for transporting goods or groups of people.In British English usage, it can be either specially designed or based on a saloon or sedan car, the latter type often including derivatives with open backs...
and placed at the end of the runway
Runway
According to ICAO a runway is a "defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft." Runways may be a man-made surface or a natural surface .- Orientation and dimensions :Runways are named by a number between 01 and 36, which is generally one tenth...
. In some cases fixed sites were installed and by the mid-1950s Standard 9 vans were in use. It was interrogated by a Rebecca
Eureka beacon
The Rebecca/Eureka transponding radar was a transponder system used as a radio homing beacon by means of a Eureka ground emitter responding to queries from an airborne Rebecca interrogator.-Operation:...
unit mounted in an aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
. It responded by transmitting dot
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...
s on one side of the runway and dash
Dash
A dash is one of several kinds of punctuation mark. Dashes appear similar to hyphens, but differ from them primarily in length, and serve different functions. The most common versions of the dash are the en dash and the em dash .-Common dashes:...
es on the other. The strength of the reception in the aircraft depended on the aircraft's position relative to the centre line of the runway. The aircraft's equipment could then determine its position relative to these dots and dashes.
This is an early version of the localiser from the more modern instrument landing system
Instrument Landing System
An instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
(ILS). The localiser uses two tones (90 and 150Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
) modulated on a carrier (108-111.975 MHz) and transmitted on a wide aperture antenna array, this can be seen at almost all airports at the end of the runway. The strengths of which (or Difference in Depth of Modulation) are detected by electronics in the aircraft and present the pilot with an indication to fly left or right and indeed up or down with a co-located glidepath (328.6 to 335.4 MHz) equipment. See instrument landing system
Instrument Landing System
An instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
for further details.
See also
- Precision approach radarPrecision Approach RadarPrecision approach radar is a type of radar guidance system designed to provide lateral and vertical guidance to an aircraft pilot for landing, until the landing threshold is reached. After the aircraft reaches the decision height or decision altitude , guidance is advisory only...
- Instrument approachInstrument approachFor aircraft operating under instrument flight rules , an instrument approach or instrument approach procedure is a series of predetermined maneuvers for the orderly transfer of an aircraft under instrument flight conditions from the beginning of the initial approach to a landing, or to a point...
- Ground-controlled approachGround-controlled approachIn aviation a ground-controlled approach , is a type of service provided by air-traffic controllers whereby they guide aircraft to a safe landing in adverse weather conditions based on radar images...