The Straight Story

A direct route may be the shortest way to go, but it may not be the quickest or the safest


Pilots who want to get from Point A to Point B are no dummies. Most of the time, the shortest distance is that straight line on the chart.

Part of the navigation training that every beginning pilot receives is how to use dead reckoning to fly that line. Getting there quickly and efficiently is, after all, one of the many benefits of flying as opposed to driving. But that direct route to the destination may not be all it is cracked up to be. Careful consideration of some of the available routing options may show that more distance is less hassle in the long run.

Although IFR pilots have more points to consider when selecting routes, VFR pilots also need to think about the dynamics of their routes.

For instrument flights, preferred routings are important to consider. Preferred routing exists as a means to safely separate arrival traffic from departure traffic at medium- and high-density airports. Whether you file the preferred route or not, the chances are excellent that you will get it.

In its generic form, most approach control airspace is set up in what is known as the corner post concept. Fixes are set up at approximately the four corners of the airspace – usually about 30 miles from the airport – and designated as arrival gates. All of the arrivals to the primary airport and most of the arrivals to the satellite airports within that approach facilitys airspace are routed over these gates. Departures are sent through the areas between the arrival gates and, with a lot of planning and a little luck, never the two shall meet.

Generally speaking, your clearance will reflect the preferred routings regardless of what you file. While it is seldom a direct route to your on-course heading, it is the safest and most efficient way to get into or out of busy airspace. Planning for the preferred route and filing it, even though it means extra miles, can save a lot of headaches, especially if youre thinking of making an end run around weather or planning to stretch fuel reserves to the limit.

Finding the routing for a particular airport isnt that difficult. A quick look at a low altitude en route chart can give you a good idea of what to expect. Look at the airspace around any busy airport and, at those points around the airport at about 30 miles there are typically four fixes with published holding patterns associated with them. Those are most likely the inbound routes to the airspace. Try filing outbound over those fixes and its a good bet youll get a routing change. Try filing inbound to the airport over points in between and chances are just as good that an amendment to your flight plan soon will follow.

Other hints on how controllers like to route departures can be found in the Airport/Facilities Directorys preferred routes section and, of course, the SIDs and STARs that are included with instrument approach plates.

The ATC limitations are obvious enough, but theyre not the only ones keeping you from your direct filing. You also need to think about the geography of your chosen route. Some of the considerations are fairly obvious. Crossing a large expanse of water means you should be prepared with flotation equipment, a second engine or enough altitude to reach dry land without engine power. Potential problems around mountains include the possibility of turbulence or bad weather. Flying over them can lead you to push your airplane to its performance limits, while mechanical problems can leave you with faced with the choice of crashing into trees or crashing into rocks.

Even the reasonably benign topography of the middle of the country can pose problems under certain conditions. Once, while taking an airplane from the Pittsburgh area to Arkansas for a paint job, I was faced with the choice of whether to fly through areas where I knew traffic could be fairly heavy or opt for the sparsely populated regions of Kentucky and Tennessee.

This was during the air traffic controllers strike and, after considering the potential for extensive delays, I opted for the more scenic route. To further complicate matters, the plane I was flying had just come back from an engine overhaul and the mechanics parting words were, We should have all the bugs worked out of it.

The flight took me over some very beautiful but highly inhospitable terrain. I remember thinking more than once that Id give a lot for an occasional airport or a highway or even some flat farmland, just in case.

Downed airplanes can be difficult to find, even when they are just a few miles from civilization. Add another hundred or so and the odds increase significantly that youll have a long time to get to know Mother Nature before the rescue crews arrive.

Granted, being over a large city isnt the best place to be if the engine quits, but usually there is a compromise route that is somewhere between Park Avenue and the boondocks.

Special Use Airspace
Prohibited areas are just that. If a controller or an amended routing tries to send you through a prohibited area, someone goofed. While you may eventually be cleared of any plot to overthrow the government, I suspect your visit with the FBI or the Secret Service prior to your exoneration wont be one you would care to repeat.

Flying through restricted areas isnt quite as cut-and-dried. Technically, if ATC clears you through restricted airspace, either because you asked for it or a controller vectors you through a restricted area based upon his or her plan, the airspace should be safe to transit.

Almost all of the time thats true. But it also happens occasionally that a section of restricted airspace can be in use for a while before word of the activity filters down to the controllers actually working with pilots.

The best way to deal with the problem is simple. If youre about to fly into a restricted area, even if youve been cleared on an IFR flight plan, make a quick call to the controller to verify that you can fly through the area without having to dodge anything that was designed to shoot airplanes out of it.

Military Operations Areas have similar requirements for IFR pilots. If ATC can guarantee you IFR separation from the military jets or helicopters operating in the MOAs, then its OK to proceed. But its not unreasonable to request verification of that separation. For VFR pilots flying through MOAs, yall be careful. Youre legally on your own.

Filing It Vs. Flying It
Another piece of the puzzle is being able to safely get from one point to another. Navigation is a sometimes mundane, sometimes thorny issue that brings with it a variety of issues to consider.

To some degree, the person who initiates the routing is responsible for ensuring no mountains or other obstructions get in the way. However, because most airspace is under radar coverage, things like Standard Service Volumes for VORs, MEAs and MOCAs tend to be ignored.

Pilots and controllers alike rely on the fact that controllers have MVAs, or minimum vectoring altitudes, that are designed to keep airplanes well clear of all obstacles, and almost all of the time they do. If the radar goes out of service, however, the best-laid plans go out with it. Even if those plans include using GPS, the problem may still remain.

Simply put, if you file it you had better be able to fly it safely. The regs are a bit more complicated than that, but they basically put the burden for determining a safe path on the person who initiates the choice. If you want to fly the airways, use the MEAs and MOCAs as appropriate and all will be well.

Fly much and youll almost certainly barrel down an airway at an altitude that is below any of the published ones. If youre in a radar environment and above the MVA, there are no unsafe obstacles – stationary ones, anyway – if the controller approves the altitude. But if the radar goes out, the controller has no choice but to require you to climb to the appropriate published altitude.

If the MEA happens to be 10,000 feet msl and youre flying a light plane at gross weight on a hot humid day, 10,000 feet just might not be possible as soon as its necessary. If thats true, wishing for a turbocharger wont get you to altitude any faster.

If you decide to make your own airways, the essential ingredients remain the same as published routes. After plotting your course (by GPS, computer or on paper), you must then determine the highest obstructions within four miles on either side of your centerline and then fly at an altitude that is at least 1,000 feet higher, 2,000 feet in mountainous terrain.

If youre using VORs for navigation, you have to be within the standard service volumes for those you plan to use. The volume depends on the terrain, but is generally a cylinder 40 nm from the station at altitudes between 1,000 and 18,000 feet. Published IFR procedures, such as Victor airways on low-altitude en route charts, may set other limits.

Either the pilot or controller can stretch those limits in a radar environment, but only if the controller monitors the flight. Once again, if the radar goes out, youre supposed to go back to flying by the book.

If the controller initiates any routing other than on an airway, then he or she is responsible for monitoring your flight path and for keeping you at or above the MVA up until the point that they get you back to some published route. While they may still allow you to fly lower than the appropriate published altitude, that is only true as long as you are identified on radar.

Even then it would be wise for pilots to stay attuned to near-by terrain, towers or other obstructions that could affect safety. Because mistakes do happen, and because pilots dont have any easy way to determine the MVA for a given route, there have been some close calls with pilots being dangerously low when flying at MVA.

Since flying IFR in a non-radar environment can be much more restrictive for a pilot than when youre on the scopes, knowing where those non-radar areas are along a certain route should have a strong influence on any decision regarding which route is really the best.

On shorter flights or those through airspace with adjacent controlled airports, pilots will be operating Tower En Route. Thats a bit of a misnomer because Tower En Route actually means working with approach control facilities instead of En Route Centers. While operating Tower En Route, you will almost certainly be operating in a radar environment. Even at low altitudes, approach control facilities will have radar coverage in almost every area under their jurisdiction. While there may be pockets through which radar coverage is unavailable, any time spent there should be brief.

If the trip operates under the control of En Route Centers, the story is likely to be different. Particularly in mountainous or even hilly areas, radar coverage at low altitudes can be sporadic. Since the Centers use long-range radar and since any radar is subject to line-of-sight restrictions, pilots need to anticipate that limited radar service could be a real consideration.

Sometimes its easy to forget just what limited radar service might mean. Some of the simplest things become difficult or impossible to obtain.

Safety alerts and traffic advisories dont really exist. And though many controllers have tried to give radar vectors in a non-radar environment, all have failed. Even deviations around weather become much more difficult when flying non-radar. Controllers cannot see the weather to give advisories, and the latitude they have to approve deviations for pilots can be limited to the width of the airway – and four miles either side of the centerline just might not be enough.

There are times when flying where radar isnt available cant be avoided. But if adding a few extra miles to your trip or gaining a bit of altitude means being under the watchful eye of the controller, its a small price to pay for a valuable safeguard.

Hitting the Bottleneck
Still another point to consider when planning your route is the potential for bottlenecks to occur along the way. The causes for the bottlenecks are sometimes a bit tough to determine, but sometimes its easy. When you want to divert because of weather, there are a dozen other pilots who want to be in the same place at the same time. Not everyone will get their wish, and it isnt always easy to know what will happen ahead of time.

Bottlenecks can also be caused by traffic and ATC procedures, in which case the results are a bit more predictable. The priority in approach control airspace is to get arrivals and departures into or out of the area as efficiently as possible. Itinerant airplanes, those just passing through the airspace on the way to someplace else, are given much less consideration. Stay outside of the arrival fixes at busy airports and youll be ahead of the game.

For example, Pittsburgh Approach Control airspace includes Victor 12, a major airway that passes through the southern half of the airspace. Not far from that airway are two of the arrival fixes for airplanes inbound to Pittsburgh and surrounding airports.

Many GA pilots transiting the area file for Victor 12, but sometimes arriving traffic has to hold aircraft at those southern arrival fixes. That leads controllers to call adjacent facilities with the news that no overflight traffic on Victor 12 can be accepted while aircraft are holding. The result is a 30- or 40-mile diversion.

Sometimes the best way to avoid the diversion is to try to fly directly over the airport. That puts a light plane in the position of causing the least amount of disruption for the shortest period of time. Generally, the more altitude you have, the more likely your request will be approved.

Controllers must be efficient at moving traffic through their airspace in order to work busy airports. Any request that helps them along with that cause is likely to be honored. So the less time you spend flying through their little chunk of the sky, the happier everyone is.

To that same end it is also always worth the effort to plan direct routes that take you farther away from congested airspace whenever possible.

Once when planning a flight from Mansfield, Ohio, to Champaign, Ill., it was clear that Indianapolis stood in the way if we took the airways. A direct route would take us farther north of Indy. Since we were RNAV equipped, my friend opted to ask for direct routing. As soon as we lifted off the runway the tower gave us direct Champaign faster than we could dial it in. Often whats good for you is even better for the controller. If you use a little common sense its almost always worth asking for a shortened route, the worst thing a controller can tell you is unable.

When a Straight Line Isnt
Even filing direct can be a little clunky, however. The best way to get to the destination isnt the shortest line to the airport, but actually the shortest line to point from which youll be vectored to the runway.

On an instrument flight, it might be best to plan to fly to the initial or final approach fix. Though the flight may well end with a visual approach, it is best to plan on flying the appropriate approach to the airport, and that starts at least 10 or 15 miles out on final.

Its not hard to make an educated guess regarding what runway or runways are in use. When checking the weather, the hourly observations and the forecasts often give an accurate clue to what runways will likely be in use when you get there. Of course, conditions may change and many airports have calm wind runways that are preferred for one reason or another, but even that information can often be obtained from a Flight Service Station.

Armed with a reasonable indication of which runway will be used, look at the approach chart and the low altitude en route chart to develop your plan. At most airports, the approaches have some kind of transition from the en route to the arrival structure. Even though youll probably get vectors to the final approach course once you pass the arrival fixes, those transitions can be the basis for good planning.

The final step in planning is then to take all that information and make your plan. Either by using the existing preferential arrival route for the direction from which you will be approaching or by looking for the arrival gate closest to your route, find the airway that will be the closest thing to a straight line to that point and put it in your flight plan.

By fitting into the flow as much as possible, the route will be slightly less direct but significantly more efficient. If ATC decides to shorten your flight by providing vectors earlier in the sequence, thats an added bonus. If not, a good plan reduces the odds of unexpected changes. Either way, thinking through all the possibilities makes for a decidedly better experience.

If youre fortunate enough to fly a plane that is all-weather, pressurized and can routinely get to flight levels for all but the shortest trips, try to get the straight line to your destination every time. Most pilots, however, dont fly airplanes that have any of that good stuff.

So while a straight line from A to B may minimize time in the air; it doesnt necessarily minimize risk while youre getting there. Its said that airplanes are a series of compromises. So, too, is the very best way to get where you are going.

At first glance that straight line can look very promising, but frequently, the more the options you explore, the more they promise to deliver.

Also With This Article
Click here to view “When Preferred Routes Arent.”

-by Milovan S. Brenlove

Milovan S. Brenlove is an assistant professor of aviation at Daniel Webster College and a former air traffic controller.


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