The Functioning of PAPI Lights

At night, you might notice many lights on the tarmac of an airport. All of them have a specific function to help guide traffic on ground and/or in the air. The PAPI lights are one of these lights.

What are PAPI lights?

No, PAPI is not only a term in parenting; it is also a crucial instrument for landing an aircraft. PAPI stands for Precision Approach Path Indicator and is located at the beginning of a runway on one or both sides. However, as a passenger you most likely never notice them, as they are located, so that the flight crew notices them and gets the needed information up to a distance of 32 km. The function of PAPI lights is defined in the ICAO Annex 14.

What do the lights tell the crew?

The lights are in white and red and indicate the optimal gliding rate for an aircraft. An aircraft that is too high might touch down too late and exceed the runway, while one flying too low might touch down before the runway starts. The optimal rate is indicated with two lights in white and two in red. The more in white, the higher the aircraft is, the more in red, the lower it is.

Student pilots have to learn the meaning and the reaction of the received information. Following simple phrases indicate the meaning of the lights:

• WHITE on WHITE – “Check your height” (or “You’re gonna fly all night”) (too high)
• RED on WHITE – “You’re all right”
• RED on RED – “You’re dead” (too low)

Are there any exceptions?

Almost all aircrafts can rely on the PAPI lights. However, there are a few exceptions, which have to adapt slightly. One of these exceptions is for the B747 – the Jumbo. As the cockpit is located quite high and behind the aircraft nose, the flight crew will typically see three white lights, which under normal circumstances would indicate a too high rate. Another exception was for the Concorde as the approach angle was supposed to be higher than with other aircrafts.

Whenever you approach an airport at night, look out for the PAPI lights in front of you. After reading this article you will understand their meaning and enjoy the view of an airport (especially during night).

Cover photo by: https://community.infiniteflight.com/t/precision-approach-path-indicator-papi/308219

Sources:

https://en.wikipedia.org/wiki/Precision_approach_path_indicator

Lukas Wopmann