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Determining Flight Speed And Route

Mon Feb 09, 2015 12:06 am

Hard to explain this question, but I know that air speed is determined by the flight plan/optimal speed/altitude for comfortable ride and fuel burn. I also know that at times route and speed are determined by ATC.

Can someone explain when it is based on the flight plan and when speed and heading are mandated by ATC. For example, I imagine its all handed over to ATC during the arrival and departure progression.

Sorry if this doesn't make a ton of sense, but hopefully someone can help explain.
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Joined: Sat Dec 15, 2012 2:25 am

RE: Determining Flight Speed And Route

Mon Feb 09, 2015 12:45 am

Quoting dcaord (Thread starter):

All of the speeds and headings are determined by the class of airspace being flown through. For instance, cruising at altitude (above 18,000ft is FL180) is Class A airspace the altitudes for planning are dictated by headings; headings 360-179 are odd altitudes (eg, FL190, FL210) while headings 180-359 are even (FL180, FL220). This general rule applies to all en-route headings (North/East ODD and South/West EVEN). Things get more complicated lower to the ground and in terminal areas, larger airports (Class B) there is an airspeed limit of 250kts while smaller airports (Class C) will have 200kts. Once handed from ARTCC to a local TRACON (Terminal area) headings ect... are generally dictated by local TRACON procedures.

There is a lot to it, if you really want to go in-depth I suggest some FAR AIM reading, Chapters 4 and 5 of the AIM should cover most of your questions.

[Edited 2015-02-08 16:50:45]

[Edited 2015-02-08 17:27:49]

[Edited 2015-02-08 17:29:23]
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Joined: Sat Jul 05, 2014 8:16 pm

RE: Determining Flight Speed And Route

Mon Feb 09, 2015 1:45 am

Quoting dcaord (Thread starter):
Sorry if this doesn't make a ton of sense, but hopefully someone can help explain.

I think what your asking is how ATC affects changes in the flight plan??

The flight plan is just that- a plan. When filed by the dispatcher, the plan adheres to all the FAR rules that the previous poster stated, and receives the scrutiny of the ATC computers. If the computer detects possible conflicts traffic wise or overlooked restrictions, then modifications are made and given to you in your clearance. This may include different altitudes than on the flight plan, different routing and possible time constraints.

Real time, the most frequent ATC speed control is during high density arrivals. Sequencing all the aircraft into an airport can get very busy for the controller and adjusting the speed of aircraft is a tool he frequently uses.

Also speed control is used frequently in non-radar environments (i.e. over the oceans). If oceanic control determines that spacing is getting a little dicey based on position reports, then they will issue clearances to either speed up or slow down. They know what your aircraft/airline speed range is acceptable.

Others may chime in with more detail.

Usually the flight plan is the most optimal way to get some where, but other factors like curfews, connection times and (rarely) crew duty time can also play a part in the plan. However if you actually fly it exactly as planned then consider yourself lucky. (pesky stuff like WX, traffic, etc tend to get in the way).

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