Runways
 

What's the longest commercial runway in the US?
What's the longest commercial runway in the world?
What do all those crazy numbers mean that are associated with runways, eg 13R 31L?

The Bay Runway is a cool nickname, can you name other runways that have cool nicknames?

Wikipedia and google are your friends.

Agreed to Halothane, you should try to do some research in google....:p

The longest commercial runway in the US is DIA (16,000 ft) followed by LAS (15,000 ft). Hot weather and high elevation are two factors that decrease lift and increase the runway length required to take off and land safely. The longest runways in the US are at Edwards AFB, California (39,000 ft).

The numbers on a runway refer to the compass direction, the runway number is the number of degrees past true north / 10. In other words if you are at the threshold of Runway 18 you are headed due south, and the other end of the runway is numbered 36. If there is more than one runway in the same direction, the leftmost would be numbered, say 18L and the rightmost, 18R. DFW has triple runways in parallel numbered 17L, 17C, and 17R (35L, 35C and 35R at the other end). LAX has 25L and 25R at the south side of the terminal and 24L and 24R at the north.

Which end of the runway is used depends on the prevailing wind direction, since it is preferable to take off and land into the wind.

In the case where there are 4 or more parallel runways, the runway number would be shifted by 1. e.g. DTW has 4 parallel runways. So, there's a 4L, 4R, 3L, and 3R. Before the 4th runway was built, the runways were labeled 3L, 3C, and 3R.

- Pat

Magnetic North

Other people have explained the numbers, so I'll give you a link to the longest runways:

http://en.wikipedia.org/wiki/List_of_longest_runways

In terms of "named" runways, here are a few I can think of:

Reef Runway (RWY 08R/26L at Honolulu)
Polderbaan (RWY 18R/36L at Amsterdam, other runways the also have names)
Startbahn West (RWY 18 at Frankfurt, used for take-offs only due to terrain issues north of the airport)

This is similar to LAX, where there are 24R, 24L, 25R, 25L.

Since it was mentioned in a prior post, I'll just add (a little off subject) that landing and taking off into the wind is advantageous since it minimizes the aircraft speed at touchdown and liftoff.

IIRC, all four are on the same heading of 35 degrees (or 215), so really they are all shifted by 0.5 :D

What was I thinking. OK, what do they do when magnetic north changes with respect to true north? Doesn't this vary as much as a couple of degrees per year?

It doesn't very by that much, but it is not that unusual to see a runway get a new identifier from time to time due to magnetic variation.

Why would you want to minimize the aircraft speed at liftoff?

Taking off into the wind gives lift.

Minimize ground speed. Also it is safer that way, as the aircraft doesn't have to travel as fast or as far to achieve the proper airspeed required to take off (lift off ;) ), known to pilots as VR ("rotate.") For example, if the aircraft is just sitting at the runway with a 10 mph direct headwind, the air speed will register at 10mph. So if the requirement for rotate is 150mph in terms of air speed, only 140 mph ground speed is required for the aircraft to leave the ground.

Note this works vice-versa, which could be dangerous! The aircraft would require a faster ground speed and in turn take more distance required to achieve the rotation speed. Lift is killed that way.

As Wiirachay explained, it's about minimising groundspeed rather than airspeed. Airspeed is defined as the speed of the air moving across the aircraft's wings, whereas ground speed is determined by the vector of the direction that air travels in addition to the vector of the aircraft's own movement relative to the air. The airspeed you need for takeoff is more or less fixed depending on the aircraft and its flap configuration, but the groundspeed corresponding to that airspeed can vary greatly depending on whether you have a headwind, tailwind, crosswind or no wind at all.

Aircraft always try to take off in a direction that gives them the most headwind possible - it takes less effort (and therefore less power, less fuel and less runway length) to reach the necessary airspeed for lift-off.