AIM ¶ 2-3-8 — Mandatory Instruction Signs
AIM 2-3-8 explains mandatory airport signs: red with white inscriptions marking runway holding positions, ILS critical areas, and no-entry zones.
Mandatory instruction signs have a red background with white inscriptions and mark places where you must stop or are prohibited from entering. These are the most critical airfield signs — crossing one without a clearance is a runway incursion.
The four types you must recognize:
- Runway Holding Position Sign: Shows the runway designation (e.g., "15-33") at the taxiway/runway intersection. Numbers are arranged to match the threshold direction — "15" on the left means Runway 15's threshold is to your left. Always co-located with holding position markings on the pavement.
- Runway Approach Area Holding Position Sign: Protects the approach/departure area of a runway. Inscription reads like "15-APCH" (approach only) or includes both approach and departure designations to keep you clear of the protected zone.
- ILS Critical Area Holding Position Sign: Marked "ILS" — used when ATC needs you to hold further back than the standard hold line to protect the ILS signal during instrument approaches.
- No Entry Sign: A red circle with a white horizontal bar — prohibits entry, typically at one-way taxiways or where vehicle roadways could be mistaken for taxi routes.
Operational takeaway: Never cross a red sign without an explicit ATC clearance for that specific runway or area.
Five FAA-written-style questions. Instant explanations, every answer cites its source — no account needed.
You are flying VFR in Class E airspace at 8,500 feet MSL during the day. What are your minimum visibility and cloud clearance requirements?