Routes and ATC

[SteveSmith]

I know this is probably a fairly simple question with a very complicated answer, but it's something I've often wondered about.

How much say do you as a pilot have in the route you take to get to your destination? Do you plan the route in detail before the flight, including each point at which you will turn, climb, descend, and what do you take into account when planning it? For example, on the BRS-EDI route that I regularly use, we always seem to go up the west coast, then turn right around Glasgow, rather than taking a straight line. Do ATC have any input into this planning? Where you are flying through airspace controlled by more than one ATC (which I guess you will on pretty much all flights), do you have to consult / agree the route with all of them? How do you do all that in a 20 minute turnaround!?

Once you are in flight, as I understand it under IFR you must obey all instructions from ATC to turn, climb, descend etc. What information do ATC have available to them about your destination and planned route as they give you these instructions, and how much do they take this into account when telling you where to go? For example, being very simplistic about it, if on the BRS-EDI route I described above, if ATC told you to turn left at Glasgow instead of right, could you say "bugger off, I'm going to Edinburgh", or would you just have to do it?

Thanks,

Steve.

[NudgingSteel]

One of my en-route colleagues might post some more detailed info for you, but very briefly I will try:
Airline flightplans are filed by the airline or handling company as 'repetetive flight plans' or RPLs. This saves huge amounts of work if the same route is flown on the same days by the same aircraft. The computer just spits the details out to ATC a few hours before the planned departure time for each flight. This gives ATC the requested route (airways, radio beacons etc), as well as the requested flight level and speed. The airline chooses the route based on which airways lead in the right direction for the quickest and cheapest trip. The pilots generally have little or no input at this stage. Climb and descent points are usually worked out by the aeroplane once the route has been input into its computer on the day, again to give the most economic profile so it has to burn the least amount of fuel. This could be modified, for example, to give a quicker trip or to avoid climbing into very busy airspace. For example, sometimes UK domestic flights might want to cruise at 24,000' or 26,000' but this might mean they are in a busy airway, and therefore pick up a slot time before departure, with perhaps an hours or more delay, before they can be accepted into that bit of airspace. By 'level capping' the flight at, say, 18,000' it might avoid the busy airspace sector and be able to depart without a slot delay, but flying at a less economical level.

The flight plan is automatically sent to all ATC units on the aircraft's route, so every controller from departure to destination airport, and all sectors along the way, know it's coming. Generally traffic is handed from one sector to another in a very routine, standard way which means it can often be done without any spoken coordination at all.

And in your Glasgow / turn left scenario, if the crew were given an instruction that they didn't agree with or understand, they would query it, hopefully more politely than your example!! It would be so incredibly rare for a pilot to simply refuse to take a turn instruction as, due to the high volume of traffic these days, one plane going where the controller doesn't want it, is going to get pretty close to several that are! The common request for unusual headings comes from the crews whilst weather avoiding.

From an ATC viewpoint, the quicker we can get an aircraft off our frequency and onto the next one, the easier our job becomes. Generally this holds true for all sectors and positions, so the fewer delays or extended routings we can give the crews, the better for everybody. (Working at an airport, though, I'm convinced that sometimes crews think we delay them just for the fun of it!!!!!)

[BOAC]

Steve - a lot of the routes are 'pre-detemined ' by EuroControl on the busier routes (and puiblished), so that is what we normally 'plan'. 'Commercial' flights are planned to be flown on airways. A 'PLOG' is issued to crew which details the route to be flown. Once airborne, it is down to the silver-tongues of the crew and the help of ATC as to what you can do with re-routes. For the example you give (BRS-EDI), up through Wales and to Glasgow, turn right is the shortest airway route. Otherwise it would be almost to London:eek: and turn left up the spine of UK = longer.

Re. "bugger off, I'm going to Edinburgh" - we normally try to find a more socially acceptable form of words.:)

[SteveSmith]

Thanks for the info. You both mention flying along "airways". As I understand it, these are basically straight lines along certain VOR radials, is this right? Presumably there are an infinite number of possible stright lines that could be flown, so why are these particular ones chosen, and who chose them?

By the way, do you actually use VOR to navigate, or is it done with GPS now?

Thanks again,

Steve.

[Globaliser]

Can't answer all the technical questions, but you might be interested to have a look at Gerd Puppel's site (http://www.planningchart.de/) to see some charts showing airways.

[Avman]

Try this too. It covers general aviation in the USA but gives you a good idea on how it all works: http://www.gaservingamerica.com/how_work/work_navigation.htm

[NudgingSteel]

An airway is basically an invisible corridor in the sky, although shown on charts and radar screens. Several miles wide and varying depths, usually several thousand feet. Depending on how cynical you are, its purpose is to either:

1. Provide a known traffic environment. All aircraft wishing to operate within (most) airways have to have a clearance from, and be talking to, and comply with instructions from, Air Traffic Control. Hence we know who's there and where they are and what they're doing, unlike 'uncontrolled' airspace which is frankly no fun at all, with military fast jets, hot air balloons and everything else you don't want mixing with your airliners! Known traffic environment = much safer, in theory....

or

2. Funnel many, many aeroplanes from all over a great big sky together, into highly concentrated narrow streams, thus ensuring the need for lots of Air Traffic Controllers to stop them getting even closer!!!! [With thanks to, I believe, the great David Gunson for that one.]