If VGSI and ILS glidepath are not coincident, which statement is accurate?

If VGSI and ILS glidepath are not coincident, which statement is accurate?

• A. The glideslope angle matches the PAPI angle
• B. The glideslope angle is steeper than the PAPI angle
• C. The PAPI/VASI lights have an angle that is different from the glideslope angle
• D. The runway heading changes

Answer: (C)

When VGSI and the ILS glidepath aren’t aligned, the visual cues on the runway and the instrument guidance don’t have to match. PAPI and VASI lights are on-site visual indicators that show whether you’re above, on, or below a target glide angle from the runway threshold. The ILS glidepath, on the other hand, is an electronic path defined by the approach system and is a fixed line in space relative to the runway centerline. If these two glide paths aren’t coincident, the angle you see from the PAPI/VASI lights can be different from the ILS glideslope angle. That’s why the accurate statement is that the PAPI/VASI lights have an angle different from the glideslope angle. The other options assume the two paths always match or bring in runway heading changes, which aren’t implied by the misalignment.

When VGSI and the ILS glidepath aren’t aligned, the visual cues on the runway and the instrument guidance don’t have to match. PAPI and VASI lights are on-site visual indicators that show whether you’re above, on, or below a target glide angle from the runway threshold. The ILS glidepath, on the other hand, is an electronic path defined by the approach system and is a fixed line in space relative to the runway centerline. If these two glide paths aren’t coincident, the angle you see from the PAPI/VASI lights can be different from the ILS glideslope angle. That’s why the accurate statement is that the PAPI/VASI lights have an angle different from the glideslope angle. The other options assume the two paths always match or bring in runway heading changes, which aren’t implied by the misalignment.