Question

Refer to ILS or LOC Rwy 13 at LGA. While flying this as a precision approach, upon breaking out of the clouds above the DA you notice that the VASI indicates that you are slightly off the glideslope. Should you continue the ILS glideslope or rely on the VASI indications?

1) Remain visual and correct your rate of descent to intercept the correct glideslope as indicated by the VASI.
2) Continue on the ILS glideslope. The VASI on this approach has a slightly different glideslope angle than the electronic glideslope of 3.1 degrees.
3) Rely on the VASI indications because they are more reliable than the electronic glideslope.
4) Continue on the ILS glideslope because the ILS or LOC Rwy 13 at LGA is an instrument approach, not a visual approach.

Answer 1

Continue following the ILS glideslope during an instrument precision approach even if the VASI indicates a glideslope discrepancy because the ILS is calibrated for specific runway characteristics and provides a more precise approach. The VASI is a visual aid with a potentially different glideslope angle.

Step-by-step explanation:

When conducting an instrument landing system (ILS) approach, such as the ILS or LOC Rwy 13 at LaGuardia Airport (LGA), pilots should adhere to the electronic glideslope to ensure the most precise approach path guided by instrument navigation. If upon breaking out of the clouds above the Decision Altitude (DA) the Visual Approach Slope Indicator (VASI) shows a discrepancy with the ILS glideslope, pilots should continue to follow the ILS glideslope. This is because the ILS provides a more precise approach path that often factors in obstacles and terrain specific to the airport.

The VASI is a visual aid designed to provide guidance information to help pilots maintain the correct approach to an airport or runway. However, a VASI may have a slightly different glideslope angle compared to the electronic glideslope provided by the ILS. The glideslope component of an ILS, typically set at 3 degrees, has a higher degree of precision due to its calibration for specific runway characteristics. Therefore, the correct approach if a discrepancy occurs is option 2: Continue on the ILS glideslope. The ILS is the primary navigation source during a precision approach, and pilots are expected to maintain the ILS glideslope until touchdown unless visual references require a slight adjustment for safe landing.