The previous lesson painted the pavement and lit the runway; this one raises the third dimension. Signs stand beside the taxiways and carry the mandatory and informative vocabulary of the movement area; markers replace lights and paint where pavement is unpaved, snow-covered or absent; and beyond the fence, every mast, chimney and wire that threatens an aircraft is coloured, flagged and lit by rules a pilot is expected to read at a glance. Twenty-three learning objectives live here, and nearly all of them come down to colours, shapes and a few memorable numbers.
Signs: the general rules
Like the light fittings of the previous lesson, signs shall be frangible, and those near a runway or taxiway sufficiently low to preserve clearance for propellers and the engine pods of jet aircraft. They are rectangular, with the longer side horizontal. And one colour rule sorts the whole system before any inscription is read: the only signs on the movement area utilising red are mandatory instruction signs. If it is red, it is an order.
Signs must be legible when the visual environment degrades. They shall be illuminated when intended for use in runway visual range conditions less than 800 m, at night in association with instrument runways, or at night with non-instrument runways of code number 3 or 4; with non-instrument runways of code 1 or 2 at night, retroreflective and/or illuminated signs suffice. A variable message sign shows a blank face when not in use, and on failure must not show anything that could lead a pilot or driver into unsafe action.
Mandatory instruction signs
A mandatory instruction sign identifies a location beyond which an aircraft taxiing or a vehicle shall not proceed unless authorised by the aerodrome control tower. It consists of an inscription in white on a red background, and the family has five members: runway designation signs, category I, II or III holding position signs, runway-holding position signs, road-holding position signs and NO ENTRY signs.
The signs pair with the painted holding-position patterns of the previous lesson, and the pairings are learning objectives in their own right:
A pattern A runway-holding position marking at a taxiway/runway or runway/runway intersection is supplemented with a RUNWAY DESIGNATION sign, located on each side of the marking, facing the direction of approach to the runway.
A pattern B runway-holding position marking is supplemented with a CATEGORY I, II or III HOLDING POSITION sign, on each side of the marking, facing the approach to the critical area; its inscription is the runway designator followed by CAT I, CAT II, CAT III, CAT II/III or CAT I/II/III.
A pattern A marking protecting an obstacle limitation surface or an ILS/MLS critical or sensitive area is supplemented with a RUNWAY-HOLDING POSITION sign: this is the sign that warns a taxiing aircraft it is about to infringe an obstacle limitation surface or interfere with radio navigation aids; its inscription is a taxiway designation and a number.
A NO ENTRY sign is provided when entry into an area is prohibited, at the beginning of the prohibited area, on each side of the taxiway as viewed by the pilot.
The inscription on a runway designation sign is the designations of the intersecting runway, properly oriented to the viewing position: "25-07" tells the pilot the threshold of runway 25 lies to the left and that of 07 to the right, except that a sign near a runway extremity may show only that extremity's designation: "25" alone. A runway designation sign at a taxiway/runway intersection is supplemented with a location sign in the outboard position (farthest from the taxiway), so the crew read WHERE they are beside WHAT they must not cross.
Information signs
Everything advisory is an information sign: direction signs, location signs, destination signs, runway exit signs, runway vacated signs and intersection take-off signs. The colour logic splits the family in two: an information sign other than a location sign is black on yellow; a location sign is yellow on black, with a yellow border when it stands alone. The location sign names the taxiway, runway or other pavement the aircraft is on or entering, and never contains arrows; every other member of the family points somewhere. Wherever practicable, information signs stand on the LEFT-hand side of the taxiway.
Runway exit sign — the designator of the exit taxiway plus an arrow; located on the same side of the runway as the exit, before the turn-off point.
Runway vacated sign — depicts the pattern A runway-holding position marking; provided where the exit taxiway has no centre line lights and the pilot needs to know when the aircraft is clear of the ILS/MLS critical/sensitive area or the inner transitional surface.
Intersection take-off sign — a numerical message giving the remaining take-off run available in metres, plus an arrow in the take-off direction.
Destination sign — a message identifying a destination on the aerodrome (cargo, general aviation) plus an arrow.
Direction sign — taxiway designator(s) plus appropriately oriented arrows; combined with a location sign, left-turn signs sit left of it, right-turn signs right of it, and the arrows lean further from the vertical as the turn sharpens.
A taxiway is identified by a letter, letters, or a combination of a letter or letters followed by a number, avoiding the letters I, O and X and words like inner and outer, for their resemblance to 1, 0 and the closed marking. The use of numbers alone on the manoeuvring area is reserved for the designation of runways. Two special members complete the system: an aircraft stand identification sign (black on yellow, supplementing the stand marking where feasible, clearly visible from the cockpit before entering the stand), and the road-holding position sign, provided at ALL road entrances to a runway: white on red, located 1.5 m from the road edge, inscribed in the national language with a requirement to stop and, where appropriate, a requirement to obtain ATC clearance and a location designator, retroreflective or illuminated for night use.
Markers
Where pavement is unpaved, snow-covered or absent, markers stand in for paint and lights; and because they stand beside the path of wings and propellers, markers shall be frangible, and those near a runway or taxiway low enough to preserve clearance for propellers and for the engine pods of jet aircraft. The same height logic as the lights and signs: struck, they must break, not bite.
Unpaved runway edge markers — where the runway's extent is unclear against the surrounding ground: flat rectangular markers of at least 1 m by 3 m laid with the long side parallel to the centre line, or cones not exceeding 50 cm in height.
Stopway edge markers — sufficiently DIFFERENT from any runway edge markers that the two can never be confused: the stopway must never invite a take-off.
Taxiway edge markers — retroreflective BLUE, on code 1 or 2 taxiways that have neither lights nor centre line markers; placed where the edge lights would have stood.
Taxiway centre line markers — retroreflective GREEN, built to withstand being run over by an aircraft's wheels without damage to either; placed where centre line lights would have stood.
Unpaved taxiway edge markers — conical markers delimiting a taxiway whose surface does not contrast with the surrounding ground.
Boundary markers — provided at an aerodrome whose landing area has NO runway: spaced along the boundary at intervals of not more than 200 m (or roughly 90 m for the conical type, with one at each corner), coloured orange or red, or in contrasting pairs of orange and white or red and white.
Marking obstacles: paint, flags and markers
Beyond the movement area, the rule for fixed objects that must be marked is a cascade: whenever practicable they shall be COLOURED; where colouring is not practicable, MARKERS or FLAGS shall be displayed on or above them, except that objects sufficiently conspicuous by their shape, size or colour need not be otherwise marked. Mobile objects to be marked are coloured or display flags: a single conspicuous colour, preferably red or yellowish green for emergency vehicles and yellow for service vehicles.
Which paint scheme an object gets is decided by its silhouette, the projection of the object on a vertical plane:
Chequered pattern — for essentially unbroken surfaces whose projection is 4.5 m or more in BOTH dimensions: rectangles of 1.5 to 3 m a side, corners in the darker colour, orange and white or red and white.
Alternating contrasting bands — where one dimension exceeds 1.5 m and the other is under 4.5 m, or for a skeletal structure with any dimension over 1.5 m: bands perpendicular to the longest dimension, about one-seventh of that dimension wide (never more than 30 m), an odd number of them, so both extremities carry the darker colour; orange and white preferred.
A single conspicuous colour — orange or red, where the projection is under 1.5 m in both dimensions: too small to pattern, bright enough to see.
Markers on or adjacent to obstacles sit in conspicuous positions preserving the object's general definition, recognisable from at least 1,000 m from the air and 300 m from the ground in every approach direction. For overhead wires and cables (the classic invisible killer crossing a valley or highway), the marker is spherical, not less than 60 cm in diameter, spaced along the wire at intervals appropriate to its size but never more than 30 m apart for the 60 cm marker, in one colour per marker with white and red or white and orange displayed alternately. Where marking the wires themselves is impracticable, high-intensity obstacle lights, Type B, on the supporting towers take over: at three levels (tower top, the lowest level of the catenary, and midway between), flashing sequentially: middle, top, bottom.
Flags on fixed objects are displayed around, on top of, or around the highest edge of the object, at least every 15 m on extensive objects, each not less than 0.6 m on a side: orange, or two triangular sections of orange and white or red and white. Flags marking mobile objects are larger, not less than 0.9 m a side, and chequered, in squares of at least 0.3 m, orange and white or red and white. No flag may increase the hazard of the object it marks.
Lighting obstacles
The presence of objects that must be lighted is indicated by low-intensity, medium-intensity or high-intensity obstacle lights, or a combination. The exam wants the families' colours and behaviour:
Low-intensity — Types A and B are fixed RED lights on fixed obstacles (Type B the brighter); Type C is the flashing yellow light of vehicles and other mobile objects (blue reserved for emergency and security vehicles); Type D the flashing yellow of the follow-me vehicle; and Type E, a flashing red light synchronised with a wind turbine's nacelle light, completes the family.
Medium-intensity — Type A flashing WHITE, Type B flashing RED, Type C fixed RED.
High-intensity — Types A and B both flashing WHITE: bright enough to work by day, which is exactly their purpose.