Pilot-controlled lighting (PCL), also known as aircraft radio control of aerodrome lighting (ARCAL) or pilot-activated lighting (PAL), is a system which allows aircraft pilots to control the lighting of an airport or airfield's approach lights, edge lights, and taxiways via radio. At some airfields, the aerodrome beacon may also be ARCAL controlled. ARCAL is most common at non-towered or little-used airfields where it is neither economical to light the runways all night, nor to provide staff to turn the runway lighting on and off. It enables pilots to control the lighting only when required, saving electricity and reducing light pollution.
The ARCAL frequency for most aerodromes is usually the same as the UNICOM/CTAF frequency, although in some rare cases, a second ARCAL frequency may be designated to control the lighting for a second runway separately (an example of this is runway 01/19 at the airport in Sydney, Nova Scotia). To activate the lights, the pilot clicks the radio transmit switch on the ARCAL frequency a certain number of times within a specified number of seconds. There are two type of ARCAL systems, type J and type K.
Type J systems are activated by keying the microphone five times within 5 seconds, while type K is initially activated by clicking seven times within 5 seconds. Once activated, the intensity of type K systems may then be turned to low, medium, or high intensity settings by keying the microphone three, five, or seven times within 5 seconds, respectively. If runway identification lights are also controlled by type K ARCAL, they may be turned off by keying the microphone three times.
When either type of system is activated, a 15-minute countdown starts, after which the lights turn off. While the lights are on, whenever a lighting command is issued, whether it changes the lighting intensity or not, the fifteen minute countdown is reset. At some airfields, the lights may flash once to warn pilots that the lights are about to go off, before turning off two minutes later.
When using ARCAL, it is strongly recommended that aircraft on final approach to the airfield issue a fresh lighting command, even if the lights are already on (especially if the lights were activated by another aircraft). This is so that the lighting does not turn off at a critical moment (such as when crossing the runway threshold). When in operation, the receiver awaits a squelch break on the tuned VHF frequency and begins counting “clicks” in a 5 second period to determine pilot intent. The pilot commanded output is held by the controller for a predetermined time interval (FAA standard is 15 minutes) that is generally adjustable. It is important to understand that the 5 second click count period begins upon receipt of the first squelch break and the control sequence will respond to the click counts from 3, 5, 7 and stop. As an example, cycling the microphone button rapidly 12 times in 5 seconds will command 3, 5, 7. Similarly, slowly clicking 7 times may result in the 5 second timing period expiring prior to getting to the 7th input click.
- Visual approach slope indicator (VASI)
- Precision approach path indicator (PAPI)
- Runway end identifier lights (REIL)
- Runway edge lights (HIRL, MIRL, LIRL)
- Approach lighting system (ALS)