What is the Calvert system?
The British centreline-and-crossbar approach lighting pattern behind ICAO practice — a 900 m white centreline of 30 m-spaced lights with five crossbars, and red side rows added for Category II and III.
The Calvert system is the British centreline-and-crossbar approach lighting design, the model for ICAO precision approach lighting on ILS runways. Its full form is a row of white lights on the extended centreline, 30 m apart, running 900 m from the threshold wherever possible, with five white crossbars at 150, 300, 450, 600 and 750 m; the 300 m bar is 30 m long. The threshold carries green lights.
For Category II and III the same 900 m centreline and crossbars are kept and two red side rows are added, extending 270 m from the threshold. In the inner 300 m the centreline is white and the side rows are red.
ICAO Annex 14 sets a smaller minimum where the centreline is built from barrettes: only the 300 m crossbar for Category I, and the 150 m and 300 m crossbars for Category II and III. The lights are fixed, variable-intensity lights. The 900 m length is set to give guidance for Category I, II and III together; shorter systems may support Category II and III but can limit Category I.
Frequently Asked Questions
Q1What is the Calvert system?
The Calvert system is the British centreline-and-crossbar approach lighting design used with ILS runways. It is named after its British designer, E. S. Calvert, and its layout is the basis of the ICAO Category I and Category II/III approach lighting systems: a white centreline running back from the threshold, with crossbars across it.
Q2What does the Category I pattern look like?
A row of white lights on the extended centreline, 30 m apart, running 900 m back from the threshold wherever possible, with white crossbars at 150, 300, 450, 600 and 750 m (the 300 m bar is 30 m long). Where the centreline uses barrettes, ICAO needs only the 300 m crossbar. The threshold itself carries green lights.
Q3What do Category II and III add?
The same 900 m centreline and crossbars plus two side rows of red lights extending 270 m from the threshold. With a barrette centreline ICAO needs only two crossbars, at 150 m and 300 m. Where the required serviceability of the lights can be demonstrated, the side rows may stop at 240 m instead. In the inner 300 m the centreline is white and the side rows are red, which gives the pilot a roll and distance-to-go cue.
Q4Why is the system 900 m long?
The 900 m length is chosen to give guidance for Category I, II and III operations. A shorter system may still support Category II and III operations, but it can impose limits on Category I operations, so a reduced length should be checked against the approved procedure.
Q5How does it compare with the FAA ALSF-1 and ALSF-2?
They do the same job with a different look. The Calvert pattern is metric: 30 m spacing and a 900 m length. The FAA systems are in feet, with barrettes every 100 ft and a length of 2,400 to 3,000 ft, and ALSF-2 adds its own red side rows and bars. Treat the two as separate standards and do not mix their dimensions.
Q6Do the lights flash?
The steady centreline, crossbars and side rows are fixed lights of variable intensity. Sequenced flashing lights may be added at some runways as an extra cue, but they are an addition to the Calvert pattern, not part of it.
Q7Is anything hazardous to work on?
Treat the circuit as live until it is isolated, locked out and proved dead under the permit-to-work. The structures are elevated and stand in the runway protection area, so access and aircraft-movement controls apply. Where flashers are fitted they are capacitor-discharge units, so discharge them as the manufacturer instructs before opening a head or cabinet.
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