when you are making a scheduled commercial flight, who decides when you have to start your descend?

Question

i mean, do you just request you want to descend when the FMC gives you the top of descent point, or does ATC decide when you have to descend?

Answer 1

This depends greatly as to where you are going. If you are going to a large airport (ATL, DEN, ORD, JFK,.........) there will be several arrivals published for each airport. Many arrivals have points specified that say "expect to cross XXXXX at 10000/250kt" or something to that effect. Many times that is exactly what ATC will instruct you to do. When you are operating in busy environments, ATC will always instruct your descent, many times much further out than you would prefer. However, when going to small airports in the middle of nowhere, such as ICT, OKC, TUL.........., you may have to ask down if you don't get it soon enough. Often times smaller airports have very little traffic to deal with and let you choose what you want to do by giving pilots discretion, such as discretion to descend and maintain 4000 when you may be higher than 18000. This gives the pilot the option to descend when they want to descend. In a perfect world, you would maintain as high as possible, as long as possible and then commence a constant descent with minimal level-offs all the way to the runway. That is the most fuel efficient way and fastest way.

Answer 2

If you are on a commercial flight, your pilot filed and will be following a flight plan. The aircraft has been given a "squawk code". ATC keeps track of your progress in flight. When you near the destination airport, ATC will contact the pilot and tell them what altitude and direction to fly in order to steer your flight to the correct end of the correct runway and keep your flight at a safe distance from other aircraft in the area. The Pilot can request a different altitude but don't count on it being granted. The pilot generally descends at a rate somewhere between 500 and 800 feet per minute. It could be a faster rate of decent but there are physical limitations to consider for both the airplane and the passengers. It could be slower rate of decent too, but ATC will request that you get to the assigned altitude quicker. The altitude of your flight is constantly update to ATC and they can tell if you are taking too much time to descend. The rate of descent really depends upon numerous factors like how high you are and how close you are to the airport when decent is started. The decent may be accomplished in 2 or 3 stages. Eventually, ATC gets you to landing pattern altitude and in the airport traffic pattern. When it is your turn to land, ATC gives the pilot clearance to land on a specific runway. The correct decent to the runway can be done by the pilot alone, or they may use a combination of flight instruments to accomplish the final decent.

Tom at http://www.lightsport.ws

Answer 3

You're responsible for flying your plane, not ATC, not the FAA, and not your FMC. If you FMC comes up with the top of descent message and you haven't been cleared for the descent, then request it. If ATC keeps you hung up for too long for traffic (or they just plain forgot, as is likely at 0530) and then clears you to descend via your arrival, they could be asking you to comply with speed and altitude crossing restrictions that would be impossible to accomplish. If that's the case, then you tell 'em that you're unable. Ball's in their court now. They'll either vector you off and then back on the arrival, or most likely delete an altitude and/or speed restriction.

In any event, you are always responsible for flying your aircraft.

Answer 4

If the ATC specialist hasn't cleared you for descent by the time you want to descend, you request it. If he instructs you to descend before you want to, then you ask to make the descent at pilot discretion, or otherwise moderate your descent rate.

Busy places like Chicago usually start you down, and you don't rush them. At more remote places you might have to prompt the controller for the descent.

Not all aircraft have an FMC.

Answer 5

normally, ATC tells you when to descend.. but you can put in a request with ATC to descend.. as long as there isn't any traffic in your flight path, they usually won't have a problem with it..

Answer 6

Either ATC will tell you or you follow a set Arrival Chart. (STAR) This chart will tell you to cross a point at a certain altitude and speed. Usually ATC will tell you what the chart says and you simply follow.

Answer 7

From what I understand, there is a set path for air traffic. The control tower will let you know when it is ok to decend.

Answer 8

Neither - the FAA