How do pilots calculate their rate of descent so that they’re at ground level when the reach the runway?
In: Other
Airliners and general aviation/business aviation airplanes on an instrument flight plan generally don’t…they file a flight plan and air traffic control tells them when to descend and “steps them down” in altitudes until they’re at the right altitude to do the final approach. Then, when they hit the glideslipe, it’s like u/SoulWager said…they follow that path down at a specific angle. Large aircraft have a dedicated Flight Management Computer (FMC) that takes the whole flight plan and does all the calculations…when to climb, when to turn, when to start descent, etc. The pilots just have to follow it, subject to air traffic control commands.
If you’re flying visual (i.e. air traffic control isn’t telling you exactly where to go) then there’s a particular altitude you want to enter the traffic pattern, usually 1000′ above the runway. So you use basic math to figure out when to start descending, like u/musicresolution describes, and you want to be at that altitude *before* you reach the airport area. Then you fly a standard traffic pattern; part of that for any airplane is learning where and what throttle setting to put in so that you lose that 1000′ to the runway in the right distance.
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