Mandatory Instruction Signs

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.

In Plain English

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.

AIM Source Text
FAA AIM ¶ 2-3-8
2-3-8. 2-3-8. Mandatory Instruction Signs These signs have a red background with a white inscription and are used to denote: An entrance to a runway or critical area; and Areas where an aircraft is prohibited from entering. Typical mandatory signs and applications are: Runway Holding Position Sign. This sign is located at the holding position on taxiways that intersect a runway or on runways that intersect other runways. The inscription on the sign contains the designation of the intersecting runway, as shown in FIG 2-3-24 . The runway numbers on the sign are arranged to correspond to the respective runway threshold. For example, “15-33” indicates that the threshold for Runway 15 is to the left and the threshold for Runway 33 is to the right. On taxiways that intersect the beginning of the takeoff runway, only the designation of the takeoff runway may appear on the sign (as shown in FIG 2-3-25 ), while all other signs will have the designation of both runway directions. FIG 2-3-26 Holding Position Sign for a Taxiway that Intersects the Intersection of Two Runways FIG 2-3-27 Holding Position Sign for Runway Approach and Departure Areas If the sign is located on a taxiway that intersects the intersection of two runways, the designations for both runways will be shown on the sign along with arrows showing the approximate alignment of each runway, as shown in FIG 2-3-26 . In addition to showing the approximate runway alignment, the arrow indicates the direction to the threshold of the runway whose designation is immediately next to the arrow. A runway holding position sign on a taxiway will be installed adjacent to holding position markings on the taxiway pavement. On runways, holding position markings will be located only on the runway pavement adjacent to the sign, if the runway is normally used by ATC for “Land, Hold Short” operations or as a taxiway. The holding position markings are described in paragraph 2-3-5 , Holding Position Markings. Runway Approach Area Holding Position Sign. At some airports, it is necessary to hold an aircraft on a taxiway located in the approach or departure area for a runway so that the aircraft does not interfere with operations on that runway. FIG 2-3-15 depicts common situations. A sign with the runway designation(s) and the protected area(s) will be located at applicable holding positions on the taxiway. For locations protecting only the approach area, the holding position on the taxiway includes a sign identifying the approach end runway designation (e.g., 15) followed by a dash (-) and the letters “APCH”. For locations protecting both the approach and departure areas, the holding position on the taxiway includes a sign with the approach end runway designation and letters “APCH” followed by a dash (-), the departure end runway designation and the letters “DEP”. The arrangement of the runway designations and protected areas legend on the sign reflects the orientation of the runway as viewed from the holding position. Holding position markings in accordance with paragraph 2-3-5, Holding Position Markings, are co-located on the taxiway pavement in line with the sign. Examples of these signs are shown in FIG 2-3-27 . FIG 2-3-28 Holding Position Sign for ILS Critical Area FIG 2-3-29 Sign Prohibiting Aircraft Entry into an Area ILS Critical Area Holding Position Sign. At some airports, when the instrument landing system is being used, it is necessary to hold an aircraft on a taxiway at a location other than the holding position described in Paragraph 2-3-5 , Holding Position Markings. In these situations, the holding position sign for these operations will have the inscription “ILS” and be located adjacent to the holding position marking on the taxiway described in paragraph 2-3-5 . An example of this sign is shown in FIG 2-3-28 . No Entry Sign. This sign, shown in FIG 2-3-29 , prohibits an aircraft from entering an area. Typically, this sign would be located on a taxiway intended to be used in only one direction or at the intersection of vehicle roadways with runways, taxiways, or aprons where the roadway may be mistaken as a taxiway or other aircraft movement surface. NOTE- Holding position signs provide the pilot with a visual cue as to the location of the holding position marking. REFERENCE- AIM, Para 2-3-5 , Holding Position Markings. FIG 2-3-30 Taxiway Location Sign FIG 2-3-31 Taxiway Location Sign Collocated with Runway Holding Position Sign
Oral Exam Questions a DPE Might Ask
Q1What color scheme identifies a mandatory instruction sign, and what does it mean?
Per AIM 2-3-8, mandatory instruction signs have a red background with a white inscription. They denote an entrance to a runway or critical area, or an area where aircraft are prohibited from entering.
Q2You're holding short and see a sign reading '15-APCH.' What does this tell you?
Per AIM 2-3-8, this is a Runway Approach Area Holding Position Sign protecting the approach end of Runway 15. You must hold so your aircraft does not interfere with operations on that runway's approach area until cleared by ATC.
Q3What is the purpose of an ILS holding position sign, and how is it identified?
Per AIM 2-3-8, the ILS Critical Area Holding Position Sign has the inscription 'ILS' and is located at a holding position on the taxiway used when the ILS is in operation, to keep aircraft from interfering with the ILS signal during instrument approaches.
Related Paragraphs in AIM Chapter 2
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AIM 2-3-8 — Mandatory Instruction Signs