The clever folks at FlightAware.com keep enhancing their product. Of late they've added useful information to the track image that they make available for each monitored flight. For example, here's what they display for N631S's flight last Friday evening from KBDR in Connecticut to VKX in the DC area:
The solid green line is the actual track of the aircraft, while the intermittent blue line is supposed to be the track of the original clearance (there are some issues at the south end). The differences in the two lines are the result of en route changes to the clearance.
Here in the busy northeast, the Air Traffic Control system is rather inflexible regarding IFR routing assignments. Unlike the great spaces of the midwest, where "Cleared as filed" is commonly heard, in these parts it doesn't matter what you file - you get the "preferred" route.
I am trainable. I now routinely file for the route that I know I'm going to get anyway: from KBDR direct SAX V249 SBJ V30 ETX V39 LRP V93 BAL direct VKX. In plain English, that says: departing Bridgeport, expect radar vectors to Sparta, NJ; then join airway V249 southbound to Solberg, NJ. From there follow airway V30 west to the East Texas VOR near Allentown, PA and take a left on airway V39 to Lancaster, PA. Then follow airway V93 to Baltimore, MD and thence direct to destination, Potomac Airfield (a.k.a. VKX).
I have that route programmed in the GNS-530W because I know I am very likely to be cleared for it. But I also know that there will be some en route changes both for the convenience of the Air Traffic Control (ATC) system and to send me expeditiously on my way.
I expect on a typical trip, for example, to be directed to the north as I depart Bridgeport. This ensures that I will pass to the north of the New York Class B airspace when I am eventually allowed to turn to the west. Also, I am usually cleared quickly to climb to 6,000 feet MSL.
The controller soon turns me to the west, toward the Carmel VOR (CMK), clears me to 7,000 feet and hands me off to the control sector responsible for the airspace north of White Plains (KHPN). This gets me above their arrivals from the north. Approaching the Hudson River, I am usually cleared up to 8,000 feet MSL and sent "direct Sparta". As I tell the auto-pilot to take me to SAX I am handed off to the Newark (KEWR) approach sector. I'm now above their southbound arrivals and often see the Boeings and Airbii passing majestically beneath my flight path.
I turn to the south at SAX, joining V249 toward Solberg...but it's rare for me to get there. I suspect that the Newark controller is on the land line with Allentown Approach, arranging the handoff. They agree that I can have a short-cut, turning a bit to the southwest to join V30 at the LANNA intersection.
Newark tells me, "Skylane 31 Sierra, proceed direct LANNA," and then a minute later, "31 Sierra contact Allentown Approach on 124.45." I respond, "124.45 for 31 Sierra...thanks and so long." I make the frequency change, listen for ten seconds to be certain I won't block someone's transmission, and then check in with Allentown.
Allentown is usually far less busy than the New York sectors (unless the weather is boisterous. See, for example, this post.) I join V30 at LANNA and motor along for a few minutes until I'm approaching a fix called BOPLY. At this point, V30 veers a bit to the north, which is not productive. But experience has taught me that if I ask nicely I will be cleared to a fix on V39 called FLOAT. It's south of East Texas and just north of the Reading, PA airport. A nice little short-cut.
Waiting for a quiet moment, I key the mike to say, "Allentown Approach, Skylane 631 Sierra, request." I hear, "31 Sierra, go ahead," and say "Any chance of direct FLOAT along here for 31 Sierra?" With no hesitation, I will normally get, "Skylane 31 Sierra, proceed direct FLOAT, join Victor 39, resume own navigation." Nice.
Nearing FLOAT, Allentown gets the next hand-off and gives me a frequency to contact Harrisburg Approach. I join V39 at Reading and turn south toward Lancaster. Harrisburg Approach is already coordinating my hand-off to Potomac Approach and my entry into the Washington, DC Special Flight Rules Area (SFRA). (On a busy night, I've been given delaying vectors, waiting for Potomac Approach to agree to my entry into their domain.) But on a typical trip, I may hear, "Skylane 31 Sierra, after Lancaster proceed direct Baltimore." Another small shortcut, and every bit helps.
Approaching the Susquehanna River, I will be directed by Harrisburg Approach to descend to and maintain an altitude of 6,000 feet. I push the nose over and accelerate to 140 knots indicated airspeed. N631S descends nicely and the speed pays me back, in part, for time lost in the climb over Connecticut.
Crossing the river I get from Harrisburg the first Potomac Approach frequency. "Thanks and so long," and I check in with Potomac.
I'm at 6,000 feet MSL which is where they want me to cross over the Baltimore-Washington International (KBWI) airport. And usually, the controller in this first Potomac Approach sector will tell me, "31 Sierra, after Baltimore proceed direct Nottingham, then direct to Potomac Airfield."
I knew that. My clearance, which is for Baltimore thence direct VKX, is really not feasible because it would take me right over Andrews AFB. Not going to happen. So I am rerouted, south from Baltimore to the Nottingham (OTT) VOR and only then direct to VKX. It adds about 10 miles to my route and avoids Andrews.
I've tried filing for OTT after BAL. Nope. Every time the ATC computer spits out "...BAL direct VKX", and every time, Potomac Approach has to reroute me to OTT. Go figure.
I cross directly over KBWI and head down to Nottingham. About 10 miles south of KBWI I will be cleared down to 4,000 feet and often, before reaching that altitude, cleared further down to 3,000 feet. If the weather is fine, the controller tells me, "Expect the visual approach at Potomac." And then, "31 Sierra depart Nottingham on heading 250." The controller is going to take me to the southwest, past VKX, and then turn me toward the airport.
Sure enough, I soon hear, "31 Sierra, descend to 2,000 and proceed direct VKX," and I turn to the northeast and look for the airport. On a good night I'll pick up the beacon fairly quickly and advise the controller that I have the field in sight. I cancel my IFR flight plan and get transferred to the local advisory frequency.
Now it's just a question of keeping the airfield in sight, making the appropriate traffic calls on the local frequency, and setting up 631S for landing.
It's good to be home.