Descending with ATC instructions?

Question

This is a question that is intended for FS. However, placing the question here instead of the "Games" section seemed like the best choice as this question does not completely fall into the Games section and is best suited here, where there are knowledgeable people that actually know how to answer my question. So don't go and tell me "This question doesn't belong here, go put it in the Games section!", etc. etc. etc.

While flying at cruise altitude, the ATC contact me and tell me to descend to a certain altitude. However, the ATC instructs me to descent at the wrong times and I cannot follow the usual descending rules that involve multiplying the distance to the airport by three, etc.

How do I know what VS to descend at?? Is there another way of calculating the VS during the descent?

Answer 1

That happens all the time in the real world. ATC often gets behind dealing with traffic and I'm happy to help them out, and required to of course. But sometimes, when it is the controllers lack of attention or other incompetence, things can become a bit contentious. I remember a time when I was given a ridiculous clearance to cross a certain intersection at an altitude that would take all of our skills as a crew and the capabilities of the aircraft to comply with. And the executives we were flying were the white knuckle type so an alarming nose down attitude was out of the question except in an emergency. It was obvious that a lackadaisical attitude was what put this particular controller in this fix.

The copilot told the controller that we'd be unable and the following dialog then took place:

Controller: "C'mon seven juliet romeo, that's what your speed brakes are for."

As the copilot was about to key his mic, I held up my hand to stop him.

Captain John B: "Nope. MY speed brakes are for MY mistakes. Not YOURS"

Of course we did have to accept a turn or two as there was traffic to contend with but we were able to deliver our usual comfortable ride to our clients.

Answer 2

Not a flight simmer, but in the real world i use the 3-6 rule (some people use a 3-5 rule).  Multiply the distance to descend (in thousands) by 3, this is the distance to begin the descent to cross a fix at a certain altitude.  Next multiply your ground speed by 6.  This is your target vertical speed.  Example:

Cross ABC at and maintain 10000, 250 kts.  You currently are  at FL250, 100 miles away from ABC flying at 400 kts ground speed.  

You have to descent 15000 ft.  (15*3=45)  You will start your descent 45 miles from ABC.

Multiply GS by 6. (400*6=2400).  You will descend at 2400fpm.  This will get you down fast enough to slow to 250 kts.  If there is no speed restriction, you can substitute the 6 for a 5.

By the way, you should plan to be around 10000 ft agl approximately 30 miles from the airport.  At least this is how it's done for real.

Answer 3

Welcome to the real world. Much more real than the other gamers' questions I've seen here. Sometimes they'll bring you down early---not good for fuel, weather, etc. Other times, they'll keep you high too long. Not just for initial descent, but at various phases of descent.

Answer 4

By VS, I assume you mean: vertical speed.

You see, all aircraft have a so-called descent profile. The computer tells the pilot when it is time to start that descent, based on the flight plan including all the STAR approach pattern, and this is fed to the autopilot that adjust the VS (that I call the VVI - Vertical Velocity Indicator).

Remember that your vertical speed is a function of your horizontal speed. Below 10,000 ft, you'll probably need to reduce speed under 250 knots. If the fraffic is very light, the controller may give you 'free speed.' Otherwise he will give you a speed that will keep you separated from other landing traffic.

The descent profile is calculated with only one purpose: to safe fuel and money. When the computer tells that it is time to start the descent, it is also the time when ATC will tell you to start your descent. If it doesn't, you will ask yourself. If it refuses, you will call your airline company via another channel and their office will in turn call by phone the ATC asking why the h**l do they keep the plane up there when it costs so much money. They better have a good excuse because ... this is all about money.

Answer 5

Since I started flying on FS in multiplayer, I had always found controller very fond of "giving orders".

Like you said, starting descent very far away from airport, giving vectors AWAY from route, etc.

I found myself asking them to continue on my flight level a little further, or not to steer away from schedules flight plan if I see no traffic.

In real life, you will just adjust your VS to a comfortable one, or let the auto pilot or flight management computer do so.

My course of action? I just set a low VS and wait for more instructions.

Cheers.