How do pilots calculate their rate of descent so that they’re at ground level when the reach the runway?
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There are many technical answers, but they can all fail. In which case, the best option is to just wing it.
Lots of good answers about instrument approaches, but I want to highlight the mark 1 eyeball. After all, even an instrument approach is finished off with a visual segment for touchdown.
Let me ask you a question: when you drive a car, how do you know exactly how much braking you need to stop by a certain point?
The answer I assume you’ll give me is that once you have a bit of experience driving, it actually becomes very natural to just look outside and be able to judge how much you need to put your foot down. Yeah maybe check your speed a couple of times, and you might need to adjust how much brake pressure you’ve used. But almost all of the time you can bring it to a nice comfortable stop at the point you intended.
Well for pilots it’s the same thing. If the weather is good they’re looking outside at the runway and can easily judge if their approach path is too high or too low. They don’t need to do any calculations by this point of the approach, and certainly aren’t just chasing a particular rate of descent. They need to be making whatever adjustments are needed to stay on the ideal approach path. But once they have completed training, this is easy to do [for most pilots…](https://en.m.wikipedia.org/wiki/Asiana_Airlines_Flight_214)
1 nautical mile is about 6,000 ft. If you’re in a small plane you do about 90 -200 knots per hour. Per min it’s 1.5 – 3.3knots per minute. If we’re at 18,000 ft and want to descend at a reasonable rate 300 -1000 ft / min. Then we divide our distance by our descent rate to get time in min. A 900fpm descent from a jet highway is reasonable, so we need to start about 20 min out (30-67 nautical miles) we can be at the ground. Usually you have to get in line to land so you aim about 1000 ft above the ground and 1 mile parallel to the runway.
We’ll have a visual check off the wings, so as we pass some big landmark like a lake or a bridge or a dam, or a big freeway we’ll start a descent. If you make the same flight a lot it’s similar to knowing when to merge to the right on the freeway so you’re ready for your exit so you’re not fighting traffic
If you do miss your exit, you can just circle and come down, but if you’re in the clouds and you miss your exit, you fly a route called a missed approach where you hold until atc gives you permission to try again.
Learn to fly. The training is expensive, but the knowledge is all online for free.
Fun fact, airplanes can’t stop, but we have stop signs called holding points, where atc tell us to fly in ovals over a radio signal. The plane has a toll that can see how hard off the signal we are in a game of Marco Polo.
… if you fly with gps you put in your destination and it tells you as you follow a magenta line “TOD” (top of descent). The gps knows how fast you’re going and even if you don’t have a fancy one that is connected to your instruments, you can input your cruising altitude into the flight plan.
I set 11 AoA with power, then put my flight path marker on the end of the runway even with the 2.5 degree pitch ladder.
The secret is that you really don’t need to be that precise. After coming in at Mach 1.2 with full afterburners, you just do a 27G barrel roll with full elevator deflection to put yourself in a semi-controlled spin to bleed off speed as you deploy full flaps and airbrakes. Then touch down at around 500km/h, without the landing gear deployed of course, and deploy the brake parachute. You’ll come to a full stop in a few seconds, so then wait for the ground crew to come and repair your mangled aircraft.
Source: I play War Thunder.
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