When does a commercial pilot know when to start the descend?

Question

When does a commercial pilot know when to start the descend?

Answer 1

VFR - descent starts as per flight plan which was submitted prior to flying.

IFR - Descents are cleared by the Air Traffic Controllers.

Answer 2

First response is correct.  A pilot can request a lower altitude if he wants to start down a bit early, but this isn't often done as fuel consumption increases at lower altitudes.  On a VFR flight plan, the pilot will plan the descent based on distance to the airport.

Answer 3

when the FMS tells him! hehe.

Answer 4

Jetsicko's method is pretty much how it's done. Every pilot has a variation of that method. It's generally 3 miles per 1000' of altitude to lose. I'm guessing that he wants to be at 10,000' 40 miles from the field so that he can slow to 250 kts and continue the descent (add a mile for every 10 kts that you wish to lose while level at 10,000 ft, another rule of thumb)

The pilot decides his climb, cruise speed and direction, and descent. If he wants to change his speed, altitude, or route of flight, he may. What has been filed in a flight plan, IFR, and particularly VFR, is not set in stone. When IFR, he'll have to coordinate with ATC before he does anything, but it's his call. The pilot flys the airplane, NOT ATC. A bad day for the pilot is a smoking hole in the ground. A bad day for a controller is when he falls out his chair and spills his coffee all over his shirt.

Answer 5

Descents are typically planned (by ATC and pilots) to be about 320ft/nautical mile.  The pilots know therir elevation above the airport, so know where to expect a descent, and where to prompt ATC if appropriate.

Answer 6

Depends on your cruise altitude, but an example...

youre at FL350. you should be at 10000ft by 40 miles out from airport. 35000-10000=25000. 25 (25000) X 3 (3.0 glide) = 75 miles + 40 out from airport =start down at 115 miles out. Take your groundspeed (600 knots lets say) and divide by 2 = 3000 FPM desent. Works every time and is usual way of doing it.

Answer 7

If you are talking to ATC on an IFR flight plan [and you will be for pretty much all commercial operations], then ATC will tell you when to descend.  Lacking that, a pilot knows how fast he/she is going and how far to descend.  Depending on the aircraft, a typical descent speed might be 500-1000 feet per minute.  So, if you know how high up you are and how fast you are going, it's pretty easy to figure out how far out you need to begin descending.

Answer 8

ATC at the arrival airport should let the pilot know by sending a message to the computer system of the plane.

Answer 9

Normally, the pilot would know because he knows what his forward speed will be in a descent, he knows how far he has to descend, and he knows his vertical speed in a descent. He can compute how long his descent will take and therefore how far forward he will travel during his descent. This is how far from the airport he must begin descending.

However, in practice, it doesn't work that way for large aircraft. Large aircraft flying into and out of large airports want to stay in the most restricted airspace they can for safety. So they're not going to descend far from an airport even if that might make the most sense. They'll stay above 18,000 feet (class A, IFR-only airspace) until they get close enough to the airport that they can descend in class B or C airspace. This helps reduce the risk of conflict with VFR (visual flight rules) traffic.

The air traffic controllers already know how the pilots want to fly and their descent characteristics, so they'll generally assign the planes lower altitudes on a sensible schedule, often leaving the pilots some discretion if possible.

Of course, if there's congestion or bad weather, optimum descents go out the window in favor of thunderstorm avoidance, aircraft stacking, and optimizing traffic flow (so you can put another airplane over the runway as soon as the previous one clears).

Answer 10

Sometimes they let the computer land the plane.