What is FAROS?
The Final Approach Runway Occupancy Signal. When the runway ahead is occupied, the PAPI beside it flashes to warn a pilot on final approach, so the warning reaches an aircraft that has not landed yet.
Entrance lights and take-off hold lights warn aircraft that are on the ground. An aircraft on final approach cannot see them. FAROS closes that gap by using something every arriving pilot already watches: the PAPI. If it flashes, the runway is not clear.
1Triggered by what is on the runway
Runway-occupancy sensors, such as inductive loops embedded in the runway or, in enhanced versions, surface surveillance data, detect an aircraft or vehicle on the runway while another aircraft is on final. The logic then decides the arrival is at risk. No controller has to switch it.
2The PAPI flashes instead of showing the glide path
The PAPI normally shows steady white and red lights that give the glide-path signal. During a FAROS warning those same lights flash. No new lights are added on the approach, and the signal is hard to mistake because the pilot is already looking at it.
3What the pilot does
A flashing PAPI means the runway is not clear. Above the contact height (about 500 ft AGL) the pilot continues with heightened awareness; at or below it, the pilot tells air traffic control and is prepared to go around, even with a landing clearance. A steady PAPI does not mean the runway is clear. The signal is a warning, not an instruction.
4What sits behind the lights
The chain is sensors, then logic, then PAPI control. The PAPI units and their power stay as they are; the added parts are the connection to the occupancy sensors and a control that makes the PAPI flash and then return to normal.
| System | Warns | Where | Signal |
|---|---|---|---|
| FAROS | Aircraft on final approach | PAPI beside the runway | The PAPI flashes |
| Runway entrance lights (REL) | Aircraft about to enter or cross | Taxiway centreline | Red in-pavement lights |
| Take-off hold lights (THL) | Aircraft in position to depart | Runway, at the departure position | Red in-pavement lights |
Frequently Asked Questions
Q1What does FAROS stand for?
Final Approach Runway Occupancy Signal. It is an FAA system that makes the PAPI lights flash to warn a pilot on final approach that the runway ahead is occupied.
Q2How does FAROS warn the pilot?
By flashing the existing PAPI lights. A pilot on approach normally reads steady white and red lights to judge the glide path. If they flash instead, the system is telling the pilot that the runway is not clear.
Q3What should a pilot do when the PAPI is flashing?
Treat a flashing PAPI as a warning that the runway is not clear. Above the contact height (about 500 ft AGL) continue with heightened awareness; at or below it, tell air traffic control and be prepared to go around, even if a landing clearance has been given. A steady PAPI does not guarantee a clear runway. Follow the operating procedures for the aircraft and the aerodrome.
Q4What triggers FAROS?
Runway-occupancy sensors, such as embedded inductive loops or, in enhanced versions, surface surveillance, feed the FAROS logic. When an aircraft or vehicle is on the runway and an arriving aircraft is on final approach, the system flashes the PAPI. No controller has to switch it.
Q5How is FAROS different from runway entrance and take-off hold lights?
Entrance lights and take-off hold lights are red in-pavement lights that warn aircraft on the ground. FAROS uses the PAPI to warn an aircraft in the air on final approach. All three act on the same idea: the system sees the runway is occupied and tells the pilot who is about to make a wrong decision.
Q6Does FAROS need new lights?
It reuses the PAPI that is already there, so no new lights are placed on the approach. What is added is the sensor connection and the control that lets the PAPI flash, and these differ at each aerodrome, so they follow the approved design.
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