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There are not many yellow markings on a runway. This row of six is painted about 400m from the threshold at both ends:

enter image description here
Montgomery Airport (Alabama) - Source: Google Maps

What does it mean for a pilot? Why yellow?

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    $\begingroup$ I count... six. $\endgroup$ – David Richerby Aug 31 '16 at 9:22
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    $\begingroup$ No, six. Runway markings are symmetrical about the centreline. $\endgroup$ – David Richerby Aug 31 '16 at 9:40
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    $\begingroup$ @mins It doesn't show on Google maps because they don't keep it strung all the time, only when they use the runway for arresting operations, and I'm guessing they close it to non-military traffic when they are doing it. I wouldn't want to hit that wire in a 172. $\endgroup$ – Ron Beyer Aug 31 '16 at 14:11
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A large number of airports in the world are used for both civil and military operations and quite a few of these have arresting systems installed on them. According to Boeing Aero No. 13:

Of the nearly 36,000 airports around the world that are classified as civil, military, or joint-use, approximately 3,800 are used for scheduled commercial service. Worldwide, an estimated 2,000 aircraft arresting systems are installed at facilities in 64 countries.

The installation criteria for cable systems on commercial runways are identified in the U.S. Federal Aviation Administration (FAA) Advisory Circular AC 150/5220-9, Aircraft Arresting Systems for Joint Civil/Military Airports.

The location of the cable is marked on the runway by a series of reflective discs 10 ft (3 m) in diameter painted "identification yellow." These discs are laid out with 30 ft (9.1 m) between centers and extend the full width of the runway.

The location of a permanent aircraft arresting system that crosses operational runway pavement will be identified by a series of reflective circles 10 feet (3.05 meters) in diameter and painted solid yellow (striated marking will not be allowed) on the runway. The circles will be 15 feet (4.57 meters) apart from edge to edge and extend the full width of the runway. The middle two circles will straddle the runway centerline.

Arresting gear marking

Arresting System Runway Pavement Marking, from FAA Advisory Circular 150/5220-9

The distance from threshold indicates whether most of the operations are conducted under visual or instrument meteorological conditions.

Runway marking

Image from Boeing Aero No. 13

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    $\begingroup$ When the cable is in place, it is at some distance from the surface. What happens to the civil aircraft rolling on it at high speed? That could also be a problem for the military ones as well, those that don't use it for landing, and for all aircraft when taking off. $\endgroup$ – mins Aug 31 '16 at 8:10
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    $\begingroup$ @mins The cables are usually held by 6" rubber donuts- so they're about 3" above the surface; the main problem is for the aircraft nosegear- especially ones with FOD deflectors, which may get snagged on the cables. If required, the cables may be made to lie flat on the runway. Another important thing is that the cables are always held under tension so as to minimize any such incidents. One more way is to use only the runway without the cables; however, this reduces the available length for to/landing. $\endgroup$ – aeroalias Aug 31 '16 at 8:16
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That would be the "line" telling military pilots where the arresting cables are. If you look to the side of those circles, you can see the arresting mechanism these. It would be yellow so that it would still stand out to the pilot and not be confused with the white runway markings.

You can find more about them here.

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    $\begingroup$ What are they used for? Practicing for landings on carriers? $\endgroup$ – gsnedders Aug 30 '16 at 20:46
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    $\begingroup$ @gsnedders These things $\endgroup$ – SMS von der Tann Aug 30 '16 at 21:01

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