What is a Mandatory Instruction Sign?
Definition
A mandatory instruction sign is a red sign with a white inscription that marks a place an aircraft or vehicle may not pass without authorisation.
ICAO Annex 14 (5.4.2.1) states the purpose. The sign identifies a location beyond which a taxiing aircraft or vehicle shall not proceed. The aerodrome control tower can authorise it. EASA CS ADR-DSN.N.780 gives the same purpose. The sign is a vertical visual aid beside the pavement. It works with the painted runway-holding position marking.
The holding position page explains the holding position as a place and lists the ICAO, EASA and FAA terms for it. This page covers the sign that shows it: the types, wording, colours, location, lighting and checks.
The types of mandatory instruction sign
ICAO 5.4.2.2 and CS ADR-DSN.N.780 list the same group. Each type has a fixed inscription.
| Sign | Inscription | Where it is used |
|---|---|---|
| Runway designation sign | The designations of the runway that the taxiway meets, turned to face the viewer | At a taxiway/runway intersection or a runway/runway intersection, with a Pattern A marking |
| Category I, II or III holding position sign | The runway designator followed by CAT I, CAT II, CAT III, CAT II/III or CAT I/II/III | At a Pattern B marking, facing the approach to the ILS/MLS critical area |
| Runway-holding position sign | The taxiway designation and a number | At a holding position that protects an obstacle limitation surface or navigation aids (ICAO 3.12.3) |
| Road-holding position sign | Set out in ICAO 5.4.7 | At the entrance of a road to a runway |
| NO ENTRY sign | The symbol of Figure 5-30 (EASA Figure N-4) | At the start of an area that aircraft may not enter |
Two details change the rule for a runway designation sign. ICAO allows a sign near a runway end to show only the designation of that runway end. ICAO also recommends a location sign next to it, in the outboard position, which is the position farthest from the taxiway. EASA CS ADR-DSN.N.785(a)(10) requires the location sign at a runway designation sign, except at a runway/runway intersection.
The FAA uses other names. The FAA AIM (paragraph 2-3-8) names these mandatory signs:
- Runway holding position sign. It shows the designation of the intersecting runway, for example 15-33. The numbers match the positions of the thresholds. On a taxiway that meets the start of the take-off runway, the sign may show only the designation of that runway.
- Runway approach area holding position sign. It holds an aircraft out of the approach or departure area of a runway. The inscription is a runway designation with a dash and APCH or DEP, for example 15-APCH.
- ILS critical area holding position sign. The inscription is ILS.
- No entry sign. It prohibits entry. The AIM says it typically stands on a one-way taxiway. It also stands where a road could look like a taxiway.
How to tell it from other signs
A mandatory instruction sign is the only red sign on the movement area. ICAO 5.4.1.5 and CS ADR-DSN.N.775(c)(3) say that red is used for no other sign.
Other signs use other colours:
- A location sign is an information sign. The FAA AIM describes a black background with a yellow inscription and yellow border. It says where the aircraft is. It does not give an instruction.
- A direction sign is also an information sign. It shows the route with arrows. ICAO Appendix 4 (Note 1 to the luminance grid) gives it a yellow background.
The taxiway guidance sign page covers the information signs, and the location sign that stands next to a runway designation sign.
Where the sign stands
ICAO 5.4.2.8 to 5.4.2.11 and CS ADR-DSN.N.780(b) set the location of each type:
- A runway designation sign stands on each side of the runway-holding position marking, facing the direction of approach to the runway.
- A category I, II or III holding position sign stands on each side of the marking, facing the approach to the critical area.
- A NO ENTRY sign stands at the start of the closed area, on each side of the taxiway as the pilot sees it.
- A runway-holding position sign stands on each side of the holding position. It faces the approach to the obstacle limitation surface or the ILS/MLS critical or sensitive area.
The distance from the pavement edge follows the runway code number (ICAO Table 5-5 and EASA Table N-1):
| Runway code number | Near side of sign to taxiway pavement edge | Near side of sign to runway pavement edge |
|---|---|---|
| 1 or 2 | 5 m to 11 m | 3 m to 10 m |
| 3 or 4 | 11 m to 21 m | 8 m to 15 m |
A sign must be frangible and low enough to clear propellers and jet engine pods. The installed height has a maximum (ICAO 5.4.1.3). The legend height of a mandatory instruction sign is 300 mm for code number 1 or 2. It is 400 mm for code number 3 or 4 (Appendix 4, item 1). For those legend heights, Table 5-5 gives a maximum installed height of 900 mm and 1,100 mm. The EASA table gives the same two maxima.
Size and luminance
ICAO Appendix 4 and CS ADR-DSN.N.775(c) set the design:
- Character height. At least 300 mm with code number 1 or 2, and at least 400 mm with code number 3 or 4.
- Colour. A white inscription on a red background. Where conspicuity needs help, a black outline on the white inscription is recommended. It is 10 mm wide for code number 1 or 2 and 20 mm wide for code number 3 or 4 (ICAO 5.4.2.13).
- Luminance. In runway visual range below 800 m, the average luminance is at least 30 cd/m² for red. For white it is at least 300 cd/m². Under the other conditions that need an illuminated sign, the figures are 10 cd/m² for red and 100 cd/m² for white.
- Luminance ratio. ICAO Appendix 4, item 5, sets the ratio between the red and white elements of a mandatory sign between 1:5 and 1:10.
When a sign needs lights
ICAO 5.4.1.7 and CS ADR-DSN.N.775(c)(4) require an illuminated sign where the sign is for use in any of these conditions:
- runway visual range below 800 m
- at night with an instrument runway
- at night with a non-instrument runway of code number 3 or 4
For a non-instrument runway of code number 1 or 2, a sign for night use may be retroreflective or illuminated (5.4.1.8).
The marking that repeats the sign
A mandatory instruction marking is the sign painted on the pavement. It is a white inscription on a red background (ICAO 5.2.16.6). Except for a NO ENTRY marking, the words are identical to the sign.
- ICAO requires the marking where a sign is impracticable (5.2.16.1).
- ICAO recommends it as a supplement where operations need it. Examples are a taxiway wider than 60 m, or the prevention of a runway incursion (5.2.16.2). See runway incursion .
- It stands on the holding side of the runway-holding position marking. The gap to that marking and to the taxiway centre line is at least 1 m. On a taxiway for aeroplanes with an outer main gear wheel span below 9 m, it is placed across the taxiway. For 9 m up to but not including 15 m, it stands on both sides of the centre line (5.2.16.3 and 5.2.16.4).
- ICAO recommends no such marking on a runway, except where it is operationally required (5.2.16.5).
The FAA uses a similar idea under another name. A surface painted holding position sign has a red background with a white inscription, and it shows the runway designators. It stands 2 to 4 ft (0.6 to 1.2 m) before the Pattern A marking. The AC uses it only on a taxiway that enters a runway directly (AC 150/5340-1M, paragraph 4.5). On a taxiway wider than 35 ft (10.5 m), one sign stands left of the centerline. The AC highly recommends a second sign on the right for two-pilot aeroplanes. The AC says that the surface painted sign is part of the standard signage requirements of 14 CFR 139.311(b)(1)(ii).
What the crew and the driver do
A mandatory instruction is not advice. ICAO 9.8.2 and EASA ADR.OPS.B.027(a) require a vehicle driver to comply with the mandatory instructions of markings and signs. The control tower may authorise otherwise.
For an aircraft, the FAA AIM sets the same rule for the marking next to the sign. At an airport with an operating control tower, a pilot must not cross a runway holding position marking without ATC clearance (paragraph 2-3-5). The AIM also says that a holding position sign gives the pilot a visual cue to the location of the marking.
Checking the signs
EASA AMC1 ADR.OPS.C.015(d) and (f) says that sign maintenance should keep the information intact and fully legible. GM1 splits the checks:
- Daily. Lamps work, inscriptions are legible, panels are not damaged, colours have not faded and nothing blocks the view. At night, check that the sign is lit correctly.
- Annual. The mounting of the sign and of its lighting, and the structure of the sign.
- After an event. After snow or a storm, check the signs that the weather can affect.
These are the aerodrome operator’s maintenance checks. A drone inspection of airfield lighting does not replace them.
Frequently Asked Questions
- What is a mandatory instruction sign?
- A mandatory instruction sign is a red sign with a white inscription that marks a place an aircraft or vehicle may not pass without authorisation. ICAO Annex 14 says it identifies a location beyond which a taxiing aircraft or vehicle shall not proceed unless the aerodrome control tower authorises it.
- What does a runway hold position sign look like?
- It is a red rectangle with white letters and numbers. The FAA calls it a runway holding position sign. Its inscription is the designation of the runway ahead, for example 15-33, arranged to match the runway thresholds. ICAO and EASA call the same sign a runway designation sign. It stands at the holding position, next to the marking on the pavement.
- What colour is a mandatory instruction sign?
- The inscription is white and the background is red. ICAO 5.4.2.12 and EASA CS ADR-DSN.N.780 say the same, and the FAA AIM describes the same colours. Red is reserved for these signs. ICAO 5.4.1.5 says that the only signs on the movement area that use red are mandatory instruction signs.
- Which signs are mandatory instruction signs?
- ICAO and EASA list five. They are runway designation signs, category I, II or III holding position signs, runway-holding position signs, road-holding position signs and NO ENTRY signs. The FAA AIM groups its mandatory signs as runway holding position, runway approach area holding position, ILS critical area holding position and no entry signs.
- Is a mandatory instruction sign the same as a hold short line?
- No. The hold short line is the runway-holding position marking, which is painted on the pavement. The sign is its vertical partner. ICAO requires a sign at each Pattern A marking and each Pattern B marking. The sign tells the pilot what the marking protects, and the marking shows the exact line.
- Where does a mandatory instruction sign stand?
- A runway designation sign or a category holding position sign stands on each side of the runway-holding position marking, facing the approach. A NO ENTRY sign stands at the start of the closed area, on each side of the taxiway. ICAO Table 5-5 sets the distance from the pavement edge. For code 3 or 4 it is 11 m to 21 m from a taxiway edge.
- Does a mandatory instruction sign need lights?
- Yes in most cases. ICAO 5.4.1.7 requires an illuminated sign in three cases. They are runway visual range below 800 m, night use with an instrument runway, and night use with a code 3 or 4 non-instrument runway. For a non-instrument runway of code number 1 or 2, a sign may be retroreflective or illuminated.
- What if there is no room for a sign?
- ICAO then requires a mandatory instruction marking on the pavement. It is a white inscription on a red background, with the same wording as the sign. ICAO also recommends it as a supplement to the sign. Examples are a taxiway wider than 60 m, or the prevention of a runway incursion.
References
- icao-annex-14-vol1
- Annex 14 to the Convention on International Civil Aviation, Aerodromes, Volume I, Aerodrome Design and Operations, Ninth Edition (July 2022, consolidated with later amendments) ICAO
- easa-ear-aerodromes
- Easy Access Rules for Aerodromes (Regulation (EU) No 139/2014), including CS-ADR-DSN Issue 7 EASA
- faa-aim-2-3
- Aeronautical Information Manual, Chapter 2, Section 3, Airport Marking Aids and Signs FAA
- faa-ac-150-5340-1m
- AC 150/5340-1M, Standards for Airport Markings, Change 1 FAA
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