In the following post, I document my learnings with respect to airport runway markings. I've always found that researching and writing helps reinforces the material and is a better way for me to learn, understand and retain the information.
I recently completed ICAO's Fundamentals of the Air Transport System online course, a great resource for those interested in aviation. The course, free to access, includes 9 modules on topics from air law and navigation to security, the environment and more. My favourite module (Airports) included some general information on the different visual aids at airports. Wanting to delve deeper into this area of an airport's operation, I decided to further study runway markings and document what I've learnt below.
ICAO's Annex 14 to the Chicago Convention publishes standards and recommended practices for Aerodromes.. While the standards are minimum requirements, national civil aviation authorities may enforce more stringent requirements. Being Canadian, I have decided to focus on Canadian airports where civil aviation is governed by Transport Canada Civil Aviation (TCCA). A list of civil aviation authorities is provided here.
Standards regarding aerodromes in Canada are provided in the 5th edition of Aerodrome Standards and Recommended Practices which you can download here. I will be using this 308-page document as a reference for most of the information presented here.
The image below was obtained from Google Maps (satellite view is a godsend) with relevant points highlighted. The runway shown is 12/30 at the Edmonton International Airport (YEG), my hometown and an airport I'm partial to. I'll go over the important runway markings starting from the bottom of the picture and moving on up.
The threshold is defined as "the beginning portion of the runway declared usable for landing by the aerodrome operator." The longitudinal strips are the threshold markings which are separated into symmetrical bars separated by a 3.6m gap centered on the centreline of the runway. Each strip within a group is 30m long, 1.8m wide, spaced 1.8m apart and begins 6m from the edge of the threshold. If these numbers are confusing, our reference document includes a handy diagram shown below.
I've read elsewhere that the number of strips gives an indication as to the width of the runway, but I couldn't find specific reference to this in Transport Canada's guide, the notable exception being a note on page 85 of the document stating that the markings shown above are for "standard runway widths." My interpretation of this is that runway widths don't have to be standardized. In any case, here is the rule of thumb with regards to the number of strips and runway width:
4 bars - 60 feet (18m)
6 bars - 75 feet (23m)
8 bars - 100 feet (30m)
12 bars - 150 feet (45m)
16 bars - 200 feet (60m)
Google Maps allows you to measure distance, so of course I used it to confirm the above. Sure enough, runway 12/30 at EIA has 16 longitudinal threshold bars for a total width of 200 feet (200.82 ft according to the image below, but that's pretty damn close!).
RUNWAY DESIGNATION MARKINGS
These markings are, as the name implies, a way to identify a runway. The two-digit number is "the whole number nearest the one-tenth of the magnetic azimuth (north), when viewed from the direction of final approach." In other words, the 2 digits indicate the direction on a compass and are always between 01 and 36 as the trailing zero is always dropped. For example, 30 on our runway would be 300 degrees on a compass. Another thing to note is that these markings don't have to be exact as they are always rounded to the nearest whole number. For example, 183 degrees would be rounded down to 180 or 18. Similarly, 187 degrees would be rounded up to 190 or 19.
Side note - I've read that the FAA requires the leading zero to also be dropped which would mean that runway 09 in Canada would simply be runway 9 in the States. Because of course things have to be different in America.
Going back to our example, my earlier reference to runway 12/30 at EIA should now make sense. Given that you cover 180 degrees when facing the opposite direction, it makes sense that 12 is what's marked on the opposite side of the runway (300 - 180 = 120, dropping the 0 gives us 12. Or, 30 - 18 = 12).
Because these markings are a visual aid - and a critical one at that - the document has dimensional requirements for the numbers and letters and these can be referenced on page 83, figure 5-3. What letters you might ask? Consider that there are a number of factors that go into deciding where a runway should be placed (prevailing winds, mostly); so, there may be instances where runways are located parallel to each other, especially in larger airports. In these cases, runways are distinguished as follows where L stands for left, C for center and R for right.
- for 2 parallel runways: "L" and "R"
- for 3 parallel runways: "L" "C" "R"
- for 4 parallel runways: "L" "R" "L" "R"
In the case of 4 parallel runways, one set of adjacent runways is numbered to the nearest one-tenth magnetic azimuth, and the other set of adjacent runways is numbered to the next nearest one-tenth of the magnetic azimuth. For example, when the magnetic azimuth is between 150.0° and 159.99°, the runway designator of the two left runways would be 15L and 15R respectively, and the runway designator of the two right runways would be
16L and 16R respectively.
Here's an example of parallel runways at Toronto Pearson, YYZ.
And here are 4 parallel runways at Hartsfield-Jackson in Atlanta, ATL.
These are located along the centreline of the runway between the runway designation markings and define the runway's centre. The markings commence 12m beyond the runway designation marking and end 12m from the runway designation marking at the opposite end. The length of each longitudinal stripe is at least 30m and the length of a stripe plus the gap is at least 50m but not more than 75m. The width of the centreline is determined by AGN, Aircraft Group Number, a means of interrelating the numerous technical specifications required for the airport and the aircraft.
TOUCHDOWN ZONE MARKINGS
The touchdown zone (TDZ) is defined as the first 3,000 ft of the runway LDA or the first third of the runway, whichever is less, measured from the threshold in the direction of landing. LDA, landing distance available, is the length of the runway available and suitable for the ground run of an aircraft landing. A great definition of LDA with illustrations is provided here, but it is essentially the amount of distance available on the runway that the aircraft can traverse after touchdown and before coming to a complete stop.
The markings are 22.5m long and 3.15m wide. The number of marking pairs along with distance of TDZ markings from the threshold is determined by LDA and is given in Table 220.127.116.11 on page 93 of the document. The following figure illustrates these requirements.
AIMING POINT MARKINGS
These are 2 conspicuous stripes mean as a visual aiming point for pilots landing an aircraft. The dimensions of the aiming point markings along with distance from threshold and lateral spacing between the inner sides of the markings all depend on LDA and are provided in Table 18.104.22.168 on page 92 and are illustrated in the figure above.
THRESHOLD AND DEMARCATION BARS AND CHEVRON MARKINGS
You might have wondered what the white bar and the yellow arrows in figures 4 & 5 are. The white bar is the threshold bar which is used on a runway when:
a) the beginning of a runway is not square with the runway centreline
b) the runway threshold is not co-located with the extremity of the opposing runway
c) a paved stopway precedes the threshold of a runway, or
d) the threshold markings are located on an intersecting runway (for example in a "T" configuration)
Examples of "a" and "d" are provided in the document, and you can see "c" illustrated in figure 4 above. The stopway mentioned above is the blast pad, an area that is prepared so as to resist erosion arising from jet exhaust or propeller wash and is identified by the chevron markings.
Demarcation bars are solid yellow bars provided where a paved stopway, blast pad or taxiway precedes the pre-threshold area of a runway. These are all illustrated below.
I wondered why the difference in the two runways in the above image - why do the markings not go all the way to the threshold bar in the image on the left? I believe it's because the pre-threshold area only goes up to the demarcation bar, the portion beyond which forms part of the TORA or take-off run available. TORA is the length of the take-off run available plus the length of the clearway and the clearway forms a part of the runway (highlighted here by the arrows).
Finally we get to arrow markings which are simply provided where a runway threshold is permanently displaced from the runway end. An illustration is provided above in figure 7 and can also be seen below at runway 33L at YYZ.
In closing, I hope this has provided you with a good understanding of and appreciation for the complex and crucial role that runway markings play in ensuring the safety of aircrafts. Obviously there are a lot more visual aids to cover, from lights to taxiway marking, wind socks and more, but those are for another day.