Before landing, without ILS, how can you get the correct vertical angle and know when you're too high or too low? I think there are some red and white directionnal lights next to the runway that can tell you if your angle is correct, but I'd like to know precisely how a nice approach is done. Do pilots sometime just figure it out because it's a habit? Is it more difficult if the runway is surrounded by an ocean? I'm talking about commercial airliners as it seems more simple with small aircrafts.
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$\begingroup$ depth perception, the runway edges side to side are parallel so you can use that to see where you are height wise $\endgroup$– ratchet freakCommented May 26, 2014 at 7:59
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1$\begingroup$ I would add, in addition to my answer, that you must be familiar with an unlighted runway, by studying the maps and making several circuits, if needed, before attempting to land. Some runways have obstacles near the runway ends (trees, antenna's, houses, etc.). A small field my father uses is quite well obstructed. $\endgroup$– CGCampbellCommented May 26, 2014 at 12:30
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2$\begingroup$ You have to train your visual system to recognize the angle of the runway edges associated with a correct approach. This happens early on in your training if your instructor is diligent at presenting a consistent approach angle for your first many demonstration approaches. $\endgroup$– user2168Commented May 26, 2014 at 15:56
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1 Answer
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PAPI
An airport might have Precision Approach Path Indicator (PAPI) lights set up. I believe these might be what you are thinking of. They are discussed in Chapter 2 of the AIM.
Here are two pictures to show them at night.
The first, shows a plane that is on the correct glide path. Firstly, they are normally installed to the left of the runway, and according to the AIM, red should be on the right, so, I believe the picture has been flipped, however you could still use them as is.
If you are right on the correct glide scope for that runway, you would see two white and two red. .2 degrees high would show three white and one red, and .5 degrees high, or higher, four white.
Conversly, .2 degrees low will show three red and one white, and .5 degrees low or lower will show all four red.
Red and White is Just Right. All Red, You're Dead.
VASI
There might also be VASI, or Visual Approach Slope Indicator, lights. These are in many different configurations. They are also discussed in the AIM at the same link I posted above. An example of a two bar VASI light setup is shown below.
The VASI lights are the two sets of two lights next to the runway (just above the row of green lights. They are set up so that white over white is too high, red and white both showing, on glidepath, and red over red is too low.
The mnemonic for those is: red over white, alright; red over red, you're dead.
For more information, there is the AIM Page, the PAPI Wikipedia Page, the VASI Wiki Page, plus there are many other pages which are useful. If you search (using Google or BING, for example) for "runway lights papi" or "runway lights vasi" you'll get many hits.
One last comment here. The correct glide path for an airport is not always the same. If there is/are an obstacle, the glide path might be higher/steeper. If the runway is lighted, using PAPI and/or VASI lights, use them! They will keep you on the correct glidepath for whatever runway you're trying to use.
Good Luck and Safe Flying!
answered May 26, 2014 at 12:00
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4$\begingroup$ All true, but sometimes there is no PAPI or VASI and the pilot is still able to land. :-) $\endgroup$ Commented May 26, 2014 at 12:32
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$\begingroup$ That's exactly what I was thinking about, but I don't understand the difference between the PAPI and VASI, though they are disposed in a different manner. And how can you lan without those lights in a big plane? $\endgroup$– user2445Commented May 26, 2014 at 12:42
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$\begingroup$ I'm sorry, in the body of the question, the OP mentions lights, so my assumption was he wanted information about runway lighting. My bad. $\endgroup$ Commented May 26, 2014 at 12:44
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$\begingroup$ A 'big plane' would not normally land at an unlighted runway. In an emergency, if you have the altitude of the runway, along with obstacles either visually identified or hopefully off of a chart, you can calculate the landing. Is that what you want to know? How to calculate things like when to start descent, from what altitude and distance? $\endgroup$ Commented May 26, 2014 at 12:48
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2$\begingroup$ @CGCampbell There are many runways, even at larger airports, that don't have vertical visual guidance. They often do land on unlight runways (during the day) and there are times that the PAPI/VASI is broken, and they don't close the runway because of it. I read his question as asking both about the lights (which you have done a great job of answering) and what to do when you don't have them (how do you get the correct angle without them). I'd add one more part to your answer describing the use of instrument approaches as a backup and a visual only approach to completely answer the question! :) $\endgroup$ Commented May 26, 2014 at 14:39