What is an Enhanced Taxiway Centerline Marking?
Definition
An enhanced taxiway centerline marking is a pair of dashed yellow lines beside a taxiway centerline that warns of a runway-holding position ahead.
ICAO and EASA write “centre line”. The FAA writes “centerline”. The enhanced marking is an addition to the ordinary taxiway centerline marking . The solid line stays. Two dashed lines run beside it, one on each side, on the approach to the runway. The centerline page covers the plain runway and taxiway centerline. This page covers only the enhancement.
What it is for
The FAA gives the purpose in AC 150/5340-1M, paragraph 4.3. The marking gives supplemental visual cues that alert pilots to an upcoming runway holding position marking, in order to minimise the potential for runway incursions. ICAO and EASA add a note. The provision of enhanced taxiway centre line marking may form part of runway incursion prevention measures (ICAO 5.2.8.4, GM1 ADR-DSN.L.570). See runway incursion .
The marking warns. It does not mark the stop point. The runway-holding position marking does that, and the mandatory instruction sign repeats it beside the taxiway. The holding position page covers the stop point itself.
Is it required?
The three rule sets differ:
- ICAO. It is a recommendation where it is necessary to denote the proximity of a runway-holding position (5.2.8.4). If an aerodrome provides it, it is a Standard that it is installed at each taxiway and runway intersection (5.2.8.5).
- EASA. CS ADR-DSN.L.570(a) uses “should”. Where provided, the marking should stand at each taxiway and runway intersection. It denotes the proximity of a runway-holding position.
- FAA. At a Part 139 certificated airport, each taxiway that intersects a runway must have two things. They are a surface painted runway holding position sign and an enhanced taxiway centerline marking (AC 150/5340-1M, chapter 4). The AC says that painting it establishes compliance with the taxiway centerline requirement in 14 CFR 139.311(a)(2).
ICAO and EASA geometry
ICAO 5.2.8.9 and CS ADR-DSN.L.570 give the layout. The enhanced marking extends from the Pattern A runway-holding position marking up to 47 m in the direction of travel away from the runway.
ICAO Figure 5-7 gives the dimensions:
- The first dash starts 0.9 m from the holding position marking.
- Each dash is 3 m long, with a 1 m gap.
- Each dash is 15 cm wide and stands 15 cm from the solid line.
- The solid yellow centre line is 15 cm to 30 cm wide.
- On a light-coloured pavement, a black background of 7.5 cm to 15 cm helps the contrast.
The standards also set four special cases:
| Case | ICAO 5.2.8.9 and CS ADR-DSN.L.570 |
|---|---|
| A second holding position marking lies within 47 m (for example, category II or III) | The dashes break 0.9 m before and after it. They continue for at least three dashes or 47 m from start to finish, whichever is greater |
| A taxiway crosses within 47 m | The dashes break 1.5 m before and after the crossing centerline. They continue for at least three dashes or 47 m, whichever is greater |
| Two centre lines converge at or before the holding position | The inner dashed line is at least 3 m long |
| Two opposing holding positions less than 94 m apart | The dashes cover the whole distance and do not pass either marking |
The value of 94 m is twice the 47 m length.
FAA geometry
The FAA marking is a pair of yellow dashes. One row stands on each side of the 6 inch (15 cm) or 12 inch (30 cm) centerline (AC 150/5340-1M, paragraph 4.3). The standard pattern is:
- The first dashes start 6 to 12 inches (15 to 30 cm) from the first solid bar of the Pattern A marking.
- Each dash is 9 ft (2.7 m) long and 6 inches (15 cm) wide, and it stands 6 inches (15 cm) from the centerline.
- The gap between dashes is 3 ft (0.9 m).
- The pattern has 12 sets of dashes with gaps and ends with a set of 6 ft (1.8 m) dashes.
The total is 12 times 12 ft plus 6 ft, which is 150 ft (45.7 m). The marking is only used on taxiways that enter a runway directly. The part between the holding position marking and the runway is not enhanced. A taxiway that only crosses a runway safety area does not get it.
A surface painted holding position sign may stand on the centerline (taxiway width 35 ft (10.5 m) or less). Then the first dashes start 36 inches (0.91 m) from the bottom of that sign. The 150 ft is then measured from the Pattern A marking to the end of the last dashes.
The AC gives these special cases in paragraph 4.3.4:
| Case | FAA rule |
|---|---|
| A taxiway crosses within 150 ft of the holding position marking | The dashes end 5 ft (1.5 m) before the other centerline crosses |
| Two holding position markings on one centerline, less than 300 ft (91.4 m) apart | Only the part between them is enhanced. Both patterns start with 9 ft dashes and meet at the midpoint |
| An ILS or POFZ holding position marking lies within 150 ft | The dashes stop 3 ft (0.9 m) before that marking |
| Centerlines converge | The outside dashes keep the 9 ft pattern. Inside dashes shorter than 5 ft (1.5 m) may be left out |
| A taxiway joins two closely spaced runways | Each enhancement ends at the runway edge unless it fits in 150 ft |
ICAO and FAA side by side
| Item | ICAO Annex 14, EASA | FAA AC 150/5340-1M |
|---|---|---|
| Starts at | Pattern A marking | Pattern A marking |
| Length | up to 47 m | 150 ft (45.7 m) |
| First dash from the marking | 0.9 m | 6 to 12 inches (15 to 30 cm) |
| Dash and gap | 3 m and 1 m | 9 ft (2.7 m) and 3 ft (0.9 m) |
| Dash width | 15 cm | 6 inches (15 cm) |
| Distance from the solid line | 15 cm | 6 inches (15 cm) |
| Status | Recommended, and a Standard where provided | Required at Part 139 airports |
Colour, border and beads
Taxiway markings are yellow (CS ADR-DSN.L.520(b)). The FAA enhanced marking is yellow and must use glass beads (paragraph 4.3). Table 1-2 of the AC requires a black border for it. The border outside the dashes is 3 to 6 inches (7.5 to 15 cm) wide. A black border never uses beads.
The FAA warns against a misuse. Do not use markings that are made for aircraft, such as enhanced taxiway centerline markings, on roadways that only vehicles use. They may lead a pilot to take the road for a taxiway (AC 150/5340-1M, roadway markings).
Inspection
The EASA AMC says to inspect all markings thoroughly at least semiannually, depending on local weather. It names peeling, discolouration, fading and deposits as reasons for corrective action (AMC1 ADR.OPS.C.015(d) and (f)). GM1 says that a night assessment, set against a daylight one, shows the reflectivity of a marking.
For this marking an inspector checks these items:
- The dashes start at the Pattern A marking and run for the full length.
- Each dash has the right length, width and distance from the solid line.
- Both rows match on the two sides of the centerline.
- The pattern breaks and ends where the special cases above need it.
- Colour, border and beads are intact.
Frequently Asked Questions
- What is an enhanced taxiway centerline marking?
- An enhanced taxiway centerline marking is a pair of dashed yellow lines beside a taxiway centerline that warns of a runway-holding position ahead. The solid centerline stays in the middle. A dashed line runs on each side of it.
- How long is an enhanced taxiway centerline marking?
- ICAO and EASA set a length of up to 47 m from the runway-holding position marking. The FAA standard is 150 ft (45.7 m). Both start at the Pattern A marking and run away from the runway. The part between the marking and the runway is not enhanced in the FAA rules.
- What do the dashes of an enhanced taxiway centerline look like?
- In the FAA pattern each dash is 9 ft (2.7 m) long and 6 inches (15 cm) wide. The gap is 3 ft (0.9 m). The pattern has 12 sets of dashes and ends with a 6 ft (1.8 m) set. ICAO Figure 5-7 shows 3 m dashes with 1 m gaps, 15 cm wide, and 15 cm from the solid centerline.
- What does an enhanced taxiway centerline tell a pilot?
- It tells the pilot that a runway-holding position marking is ahead. The FAA says it gives supplemental visual cues to cut the chance of a runway incursion. ICAO says it may form part of runway incursion prevention measures.
- Is an enhanced taxiway centerline marking mandatory?
- It depends on the rule set. ICAO recommends it where the proximity of a runway-holding position needs to be shown, and EASA gives the same recommendation. Once provided, ICAO requires it at each taxiway and runway intersection. At a US Part 139 airport, the FAA requires it on every taxiway that intersects a runway.
- Where does an enhanced taxiway centerline stop?
- It stops at the runway-holding position marking where it starts, and it ends earlier where another marking gets in the way. At a taxiway intersection within 47 m, ICAO breaks the dashes 1.5 m each side of the crossing centerline. The FAA ends them 5 ft (1.5 m) before it. Between two holding positions less than 94 m apart, ICAO runs the dashes over the whole gap.
- Does an enhanced taxiway centerline have a black border?
- On a light pavement, yes. FAA AC 150/5340-1M Table 1-2 requires a black border and glass beads for the marking. The border outside the dashes is 3 to 6 inches (7.5 to 15 cm) wide, and it never uses beads. ICAO Figure 5-7 shows a black background of 7.5 to 15 cm on light-coloured pavements.
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-ac-150-5340-1m
- AC 150/5340-1M, Standards for Airport Markings, Change 1 FAA
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