A pilot briefing an ILS approach notes the straight-in minimums line reads: 'S-ILS 27, DA 200 (200-1/2)' with a remark stating RVR 1800 is authorized in lieu of 1/2 SM based on installed touchdown zone and centerline lighting. Why does this lighting configuration allow a lower visibility minimum than a standard ILS without TDZ/CL lights?
- ATDZ and CL lighting increase the localizer signal strength, improving lateral guidance accuracy near the runway
- BTDZ and CL lighting are required by regulation for any Category I ILS regardless of minimums
- CTDZ and CL lighting extend the missed approach point further down the runway, permitting a lower decision altitude
- DTouchdown zone and centerline lighting provide additional visual cues for depth perception and centerline tracking during the flare, allowing operations to a lower RVR under 14 CFR 91.175(f)
Show answer & explanationAnswer & explanation
Correct answer: D. Touchdown zone and centerline lighting provide additional visual cues for depth perception and centerline tracking during the flare, allowing operations to a lower RVR under 14 CFR 91.175(f)
14 CFR 91.175(f) allows reduced visibility minimums (down to RVR 1800) when specified lighting aids such as touchdown zone and centerline lighting are installed and operating, because they give the pilot enhanced visual references for landing in reduced visibility, not because they affect the navigation signal.
Why the other options are wrong
- A. Incorrect — lighting has no effect on localizer signal strength
- B. Incorrect — TDZ/CL lighting is not mandatory for all ILS approaches, only for certain minima
- C. Incorrect — lighting does not move the MAP or affect the DA
Approach Lighting Visibility Credit
Certain approach lighting systems (e.g., touchdown zone and centerline lights) allow ATC/FAA to authorize reduced visibility minimums under 14 CFR 91.175(f) because they enhance visual references during landing.
- TDZ/CL lighting can reduce required visibility from 1/2 SM (2400 RVR) to 1800 RVR
- Credit is codified in 91.175(f), not by increasing signal accuracy
- Charts note the specific lighting basis for reduced minimums
Memory trick: More lights, more sight, lower minimums allowed.