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4.2. Taxiway centerline markings.
a. Purpose. The taxiway centerline marking provides pilots continuous visual guidance to permit taxiing along a designated path. See AC 150/5300-13 for standard fillet design, AC 150/5340-30 for lighting provisions and AC 150/5340-18 for signage provisions.
b. Requirement. All taxiways, regardless of their width, have a surface painted taxiway centerline.
c. Location. On a straight section of a taxiway, the taxiway centerline marking is located along the physical centerline of the paved taxiway. This statement assumes the taxiway was built to standard, i.e., symmetrical with a taxiway centerline. On curved sections of a taxiway, the taxiway centerline marking continues from the centerline marking of the straight portion of the taxiway along a curved centerline defined in AC 150/5300-13.
For taxiways that intersect other taxiways, the adequacy of the fillet design (1)determines the centerline painting scheme as shown in Figure A-18. The standard design is cockpit-over-centerline steering, which reduces the number of airplane main gear excursions from the taxiway.
(i) At taxiway intersections with fillets that do not meet the fillet design standards of AC 150/5300-13 for the Taxiway Design Group (TDG) of the taxiway —that is, judgmental over-steering is performed by pilots—the centerline marking continues straight through the intersection as shown at the top Figure A-18. This practice applies to intersecting taxiways that are or are not of the same TDG.
(ii) Where fillets are designed to the TDG of the taxiway, the taxiway centerline marking follows the taxiway curve as shown on the bottom of Figure A-18 to permit cockpit-over-centerline steering operations. This practice applies to intersecting taxiways that are of the same TDG.
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Note: AC 150/5300-13 states that cockpit-over-centerline steering is the standard methodology for painting taxiway centerlines in taxiway intersections. To reduce taxiway excursions on turns, airport operators should (1) construct standard fillets and (2) paint taxiway centerlines according to cockpit-over-centerline design.
For taxiways that intersect runways, different painting requirements or (2)restrictions apply.
(i) For a taxiway that intersects a runway at a runway end, as shown in Figure A-16 and Figure A-17, the taxiway centerline is terminated either at the runway edge or at the outer edge of the runway edge marking. However, the taxiway centerline (lead-on and lead-off) will continue onto the runway under the following conditions:
(a) Where there is a displaced threshold, as shown in Figure A-7 and Figure A-11, the taxiway centerline marking continues onto the displaced area of the runway and extends parallel to the displaced threshold markings (arrow heads and arrow shafts) for a distance of 200 feet (61 m) beyond the point of tangency or terminates at the point of contact with the displaced threshold bar, whichever is less. As shown in Figure A-8, the lead-on and lead-off taxiway centerlines are 3 feet (1 m) from the runway arrow markings as measured near-edge to near-edge. This lead-on or lead-off taxiway centerline line is interrupted for all runway markings with some exceptions (see paragraph 4.2.c(2)(i)(b)).
(b) For low-visibility taxiing operations, when the runway visual range (RVR) is below 1,200 feet (366 m), the taxiway centerline marking continues across all runway markings with the exception of the runway designation marking and, unless required by a SMGCS Plan, the runway threshold marking (longitudinal stripes). The painted taxiway centerline marking must follow the path of the in-pavement lighting criteria of AC 150/5340-30. That is, if the in-pavement lighting is curved, the painted taxiway centerline is curved. In this situation, the taxiway centerline marking continues onto the runway and extends parallel to the runway centerline marking for a distance of 200 feet (61 m) beyond the point of tangency and is 3 feet (1 m) from the runway centerline as measured near-edge to near-edge. For some airfield geometry, such as an airfield with parallel runways with several parallel taxiways, the painted taxiway centerline at the runway end is painted straight through the runway end and curved onto the runway. See AC 150/5340-30 for the different RVR in-pavement lighting requirements and recommendations associated with various airfield configurations.
(ii) For taxiways that intersect a runway at any other locations than at the runway end, as shown in Figure A-16, the taxiway centerline marking curves onto the runway and extends parallel to the runway centerline marking for a distance of 200 feet (61 m) beyond the point of tangency with the runway centerline or terminates at the point of contact with the displaced threshold bar, whichever is less. As shown in Figure A-16 and Figure A-17, these lead-on and lead-off taxiway centerlines are 3 feet (1 m) from the runway centerline when measured near-edge to near-edge.
(a) For taxiways that cross a runway, which are either perpendicular to or non-perpendicular to the runway centerline, and are normally used as
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crossing taxi routes, the taxiway centerline marking may continue across the runway but is interrupted for all runway markings with some exceptions (see paragraph 4.2.c(2)(i)(b).
(b) For low-visibility taxiing operations, when the RVR is below 1,200 feet (366 m), the taxiway centerline marking continues across all runway markings with the exception of the runway designation marking and, unless required by the SMGCS Plan, the runway threshold marking (longitudinal stripes), aiming point marking, and the touchdown zone markings.
d. Color. The taxiway centerline marking is yellow. See paragraph 1.4 and Table 1-1 for required and recommended techniques to enhance this marking.
Painting Notice: Over the years, some airport operators have installed other colors to denote various taxiing routes on the movement areas. These surface markings are non-standard. In an attempt to circumvent the yellow color standard, these different colored centerline markings have sometimes been referred to as supplemental markings or some other ambiguous term. Regardless of what they are called, these surface markings are non-standard and require specific approval by the FAA Director of Airport Safety and Standards. Regarding aircraft deicing facilities that are located in a non-movement area, taxiway/taxilane centerlines are painted in accordance with AC 150/5300-14, Design of Aircraft Deicing Facilities.
e. Characteristics.
Width. The taxiway centerline marking width, which is either 6 inches (15 (1)cm) or 12 inches (30 cm), is based on the type of taxiing operation as described below. Uniform width must be maintained for the entire length of the taxiway except under the following conditions.
(i) The taxiway or part of the taxiway is designated as a SMGCS taxi route. Under this designation, the width of the taxiway centerline must be 12 inches (30 cm) wide and, on light-colored pavement, further outlined in black. The taxiway centerline width of any remaining section of the taxiway that is not part of the designated SMGCS taxi route may change abruptly at that point or at the intersection with other taxiway centerline markings, for example, reduced from 12 inches (30 cm) to 6 inches (15 cm).
(ii) A confusing intersection of taxiways is better served by the designation of a preferred taxi route through the confused intersection by painting a wider centerline width. The FAA recommends that airport operators take measures to realign or reconstruct confusing taxiway intersections.
(iii) If deemed necessary by the airport operator to provide pilots a better visual clue of the location of troublesome taxiway exits from the runway, the airport operator may increase 6-inch (15-cm) wide taxiway centerline markings before the aircraft hold side at the runway holding position location to 12-inch (30-cm) wide lead-off taxiway centerline markings on the runway side.
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Discontinuity of the Taxiway Centerline Marking Along the Taxiway. The (2)taxiway centerline marking of a taxiway remains continuous except when it intersects (1) a runway holding position marking, (2) an intermediate holding position marking (intersection of taxiways), (3) an ILS/MLS or POFZ holding position marking, or (4) non-movement area boundary marking (paragraph 5.4). Figure A-13 and Figure A-14 illustrate the marking details for most of these conditions.
I hope this helps
Best reguards
Wolfgang
