How Do You Interpret a VASI and a PAPI, and What Do the Light Colors Indicate?

Why VASI and PAPI Matter on Your Checkride

Visual approach slope indicators are among the most practical tools in a pilot's instrument scan during landing, and your Designated Pilot Examiner (DPE) knows it. These systems exist at thousands of airports across the country, and understanding exactly what those red and white lights are telling you is both a checkride requirement and a genuine safety skill. The Aeronautical Information Manual (AIM), in its Airport Lighting section covering VASI and PAPI, lays out the standards clearly — and your DPE expects you to know them cold.

The good news is that once you understand the logic behind these systems, the interpretations are straightforward. The bad news is that a surprising number of students reverse the color meanings under pressure and end up telling their examiner that all red means too high. That single mix-up can cost you credibility on an otherwise strong oral. Let's make sure it does not happen to you.

Reading the VASI: Two Bars, Three Possible Indications

A VASI — Visual Approach Slope Indicator — consists of two separate bars of lights positioned alongside the runway. The near bar sits closer to the runway threshold, and the far bar sits farther down the runway. Each bar projects either a red light or a white light depending on your vertical position relative to the glidepath, which is typically set at approximately three degrees.

The correct glidepath indication is red over white — meaning the near bar shows red and the far bar shows white. The memory aid that every pilot learns early and every examiner loves to hear is: 'red over white, you are alright.' When you see that combination, you are precisely on the intended approach slope and can expect safe clearance over all obstacles and terrain in the approach corridor.

If both bars appear red, you are below the glidepath. The classic memory phrase is 'red and red, you are dead' — blunt, but effective. This is the indication that demands immediate corrective action, because descending below the glidepath means you may be losing obstacle and terrain clearance. Students frequently make the mistake of reversing this, claiming that all red means too high. It does not. Red is the low-energy, low-angle color. Think of it this way: the lower you are, the more red lights you see, because you are looking up at the underside of the light housings.

If both bars appear white, you are above the glidepath — 'white and white, you are in flight.' While being high is generally safer than being low from an obstacle clearance standpoint, it does increase your risk of landing long or floating down the runway. Recognize it and correct it.

Reading the PAPI: Four Lights, Five Precise Indications

A PAPI — Precision Approach Path Indicator — takes the same concept further. Instead of two bars, it uses a single horizontal row of four lights, viewed from the cockpit as you approach the runway. Because there are four individual lights rather than two grouped bars, the PAPI gives you a finer gradient of glidepath information — five distinct indications instead of three.

Here is how to read the PAPI from left to right as seen from the aircraft:

• All four white: You are significantly above the glidepath. Descend promptly.
• Three white, one red: You are slightly high. Make a small correction downward.
• Two white, two red (white on the left, red on the right): You are on the glidepath. This is the target indication.
• One white, three red: You are slightly low. Apply power and climb back to the slope.
• All four red: You are significantly below the glidepath. This requires immediate corrective action — obstacle clearance is in question.

A common point of confusion on checkrides is mixing up the VASI and the PAPI entirely. Remember: VASI uses two separate horizontal bars, while PAPI uses four lights arranged in a single horizontal row. They serve the same fundamental purpose and both provide roughly a three-degree glidepath, but their physical appearance and the number of indications they offer are different. If your examiner asks which system provides more precision, the answer is the PAPI.

The Safety Principle Behind Both Systems

Whether you are shooting an approach to a towered international airport or a small uncontrolled field, the underlying principle is the same: stay on or above the glidepath. The FAA designs visual approach slope systems to ensure that a pilot on the correct slope will clear all obstacles and terrain within the approach corridor. Dipping below that slope — even briefly — removes that assurance. This is why 'all red' on either system is treated with urgency, not casual correction.

When your DPE asks about VASI and PAPI during your oral, they are not just testing memorization. They are confirming that you understand why these systems exist and what actions to take based on what you see. Pair the color mnemonics with the underlying safety logic, and your answer will stand out.

If you want to practice questions like this in a realistic oral exam format, try SimulatedCheckride.com.