Editing Instrument landing system (section)

==Approach lighting==
{{Main article|Approach lighting system}}
[[File:Odate-Noshiro Airport Approach light.jpg|thumb|[[Odate–Noshiro Airport|Odate-Noshiro Airport]] approach lighting system.]]


Some installations include medium- or high-intensity [[approach lighting system|approach light systems]] (abbreviated ''ALS''). Most often, these are at larger airports but many small general aviation airports in the U.S. have approach lights to support their ILS installations and obtain low-visibility minimums. The ALS assists the pilot in transitioning from instrument to visual flight, and to align the aircraft visually with the runway centerline. Pilot observation of the approach lighting system at the Decision Altitude allows the pilot to continue descending towards the runway, even if the runway or runway lights cannot be seen, since the ALS counts as runway end environment. In the U.S., an ILS without approach lights may have CAT I ILS visibility minimums as low as {{convert|3/4|mi|km}} (runway visual range of {{convert|4,000|ft|m}}) if the required obstacle clearance surfaces are clear of obstructions. 
[[File:Approach lighting system at Aurel Vlaicu International Airport.jpg|thumb|Approach lighting system at [[Aurel Vlaicu International Airport]].]]


Visibility minimums of {{convert|1/2|mi|km}} (runway visual range of {{convert|2,400|ft|m}}) are possible with a CAT I ILS approach supported by a {{convert|1400|to|3000|ft|m|adj=mid|-long}} ALS, and {{convert|3/8|mi|m}} visibility {{convert|1800|ft|m|adj=on}} visual range is possible if the runway has high-intensity edge lights, touchdown zone and centerline lights, and an ALS that is at least {{convert|2400|ft|m}} long (see Table 3-3-1 "Minimum visibility values" in FAA Order 8260.3C).<ref>[https://www.faa.gov/documentLibrary/media/Order/FAA_Order_8260.3C.pdf FAA Order 8260.3C, United States Standard for Terminal Instrument Procedures (TERPS)] {{webarchive|url=https://web.archive.org/web/20170513030853/https://www.faa.gov/documentLibrary/media/Order/FAA_Order_8260.3C.pdf |date=2017-05-13 }}, effective 2016-03-14, accessed 2017-12-04</ref> In effect, ALS extends the runway environment out towards the landing aircraft and allows low-visibility operations. CAT II and III ILS approaches generally require complex high-intensity approach light systems, while medium-intensity systems are usually paired with CAT I ILS approaches. At some [[non-towered airport]]s, the [[Pilot Controlled Lighting|pilot controls the lighting system]]; for example, the pilot can key the microphone seven times to turn on the lights on the high intensity, five times to medium intensity or three times for low intensity.{{cn|date=December 2022}}