FAA Instrument Flight Instructor (FII)Instruments and SystemsMedium
A CFII is briefing a student on ILS glide slope characteristics prior to an approach. The instructor correctly explains that full-scale deflection of the glide slope needle represents approximately
- A5 degrees above or below the glide path centerline
- B0.7 degrees above or below the glide path centerline
- C0.35 degrees above or below the glide path centerline
- D2.5 degrees above or below the glide path centerline
Show answer & explanationAnswer & explanation
Correct answer: B. 0.7 degrees above or below the glide path centerline
The glide slope beam is much narrower than the localizer beam; full-scale fly-up or fly-down deflection represents approximately 0.7 degrees above or below the nominal glide path, which is typically set at 3 degrees. This narrow tolerance requires precise pitch and airspeed control during final approach.
Why the other options are wrong
- A. 5° is not associated with glide slope sensitivity; it is unrealistically large for a precision approach aid.
- C. 0.35° is half of the actual full-scale deflection value, not the full value.
- D. 2.5° is far too large; this would represent an enormous vertical deviation not consistent with published glide slope tolerances.
ILS Glide Slope Sensitivity
The ILS glide slope provides vertical guidance to a 3° glide path, with full-scale needle deflection representing about 0.7° above or below that path.
- Standard glide path angle is 3 degrees
- Full-scale deflection ≈ 0.7° from centerline
- Localizer full-scale deflection is wider, about 2.5° at the runway
- Glide slope transmitter located near the runway touchdown zone
Memory trick: Loc gives left-right, Glide gives up-down, Markers give distance milestones.