How to determine a plane’s heading
January 15th, 2007 at 9:12 pm (Technology)
A friend offered this great tidbit of information:
The navigation lights on the airplane wings are red on the left side and green on the right side, so that people on the ground and in the air can tell at a glance at night which direction the plane is heading.
It turns out that ships do this, too, and it not only permits the determination of direction but also the resolution of right-of-way questions. From wikipedia:
If he sees green, he is to the impinging craft’s starboard and has the right of way. If the pilot sees the red light, he knows that the approaching craft has the right-of-way, and he is required to deviate from his course to avoid the collision.
So the next time you’re near an airport at night, look up and see if you can detect both colors in approaching or departing planes (you’ll then be able to tell which is which).
Thanks, Leighton! (And thanks to Jim for his addenda, in the comments.)
jim said,
January 15, 2007 at 10:59 pm
Random other nuggets:
Newer airplanes (which means “less than 21 years old”, though it also applies to other aircraft) also have an anti-collision light system, including a beacon (on the tail) and white strobe lights on the wings. The pilot has the discretion on operation of the latter. (I found them very distracting during night time operations where there was any visible moisture.)
Inoperative navigation lights will ground an aircraft.
Under VFR conditions in controlled airspace*, when a plane is flying a heading of 0 – 179, they typically maintain altitudes of 3,500, 5,500, 7,500 … 17,500 while on headings of 180 – 359, it’s 2,500, 4,500, 6,500 … 16,500. (*Above 18,000, instrument conditions prevail and it’s odd and even thousands, respectively; closer to the ground, things get more complicated as various airspaces — Classes G, E, D, C, and B apply.)
Leighton said,
January 18, 2007 at 7:45 pm
The colored lights can be pretty hard to see sometimes, depending on the distance and whether there’s a street lamp or lighted building close enough (arcwise) in your field of vision. With an untrained eye, I estimate that the collision beacon is 3-5 times as bright (intense?) as the nav lights, and the white strobes on the wings are about twice as bright. These figures seem to depend on the model of plane, though.
(There are perks, I suppose, to living and working underneath a couple dozen LAX flight paths. :))
jim said,
January 18, 2007 at 11:40 pm
Relative minimum brightnesses for a single-engine aircraft (YMMV):
The tail and wing strobes: 2,000cd
Wingtip (red & green) navigation lights: 400cd
Landing light: 40,000cd (Small aircraft are requested to have their landing light on while in the pattern)
Taxi light: 6,000cd
For comparison, a car headlight is 75,000cd.
jim said,
January 18, 2007 at 11:43 pm
Clarification: the taxi light is typically located next to the landing light, right on the cowling, below/behind the propeller. Commercial jets typically have these embedded in the wing.