PAPI (Precision Approach Path Indicator)

PAPI (Precision Approach Path Indicator) is a visual aid installed beside the runway that provides glidepath guidance to pilots during visual approaches. It consists of four light units that show red or white depending on the aircraft's position relative to the desired glidepath (typically 3°).

• 4 white = too high
• 3 white + 1 red = slightly high
• 2 white + 2 red = on glidepath (correct)
• 1 white + 3 red = slightly low
• 4 red = too low (dangerously low)
• Visible from approximately 5 NM in daylight
• Standard glidepath angle: 3.0° (can be steeper at airports with terrain constraints)