There are four basic problems you will encounter in everyday use of VOR. Whether you’re holding, executing an approach, or navigating enroute, a thorough knowledge of these four will enable you to han- dle any situation. They are:
1. Determining what course will take you direct to a VOR.
2. Determining your position in relation to a specific airway or radial. 3. Identifying an intersection (or crossing a particular radial). 4. Determining a wind correction angle that will keep you on
course.
The first case is frequently put to use when you are cleared “from your present position direct ” to a VOR. The procedure is simple; after tuning and identifying the station (don’t ever forget this step!), 114
rotate the OBS until the left-right needle is centered and the ambi- guity indicator shows TO. The number that now appears under the OBS index is your course to the station (inbound, it will always be the
reciprocal of the radial you are on); turn to and fly that heading, ap-
plying drift correction as necessary to keep the needle centered, and that’s all there is to it.
The second case starts off the same way; when you are requested to “intercept and fly outbound on the 320 radial,” make certain you have the right station tuned and select 320 on the OBS (since you are outbound, desired course and radial are the same). If you’re not on that heading or close to it, turn to 320 degrees to satisfy the first con- dition of VOR orientation. Assuming that when you received the clear- ance you were already northwest of the VOR, the TO-FROM indicator should settle on FROM. (If you’re located somewhere else, keep flying on a 320 heading; you’ll get a FROM sooner or later.) So far, so good; now to the heart of the problem: Where are you in relation to the 320 radial? If the CDI centers, you’re there, and because you turned the air- plane to bring the heading into agreement with the OBS setting, a de- flection of the needle to either side will tell you which way to turn to get on course. Needle left? Fly left, and vice versa. The same procedure applies when you’re cleared to fly a radial inbound (don’t forget to re- verse the numbers), except the TO-FROM indicator will read TO.
The third situation comes up frequently, such as when you’re checking groundspeed, temporarily out of radar contact, timing a holding pattern, or asked to report at an intersection. Reporting points are usually the well-defined crossing of two or more airways or radials. Whether you’re asked to report at a named intersection or when crossing a certain radial, there’s a technique that will work every time. For example, if you are proceeding northwest from the Peoria VOR on Victor 434 (Fig. 9-1) and the controller requests a re- port passing the VICKS intersection, you have a choice of either the 061 radial of the Burlington VOR or the Bradford 247 radial as your cross-reference. The Bradford radial seems best because you will be closer to that station and the bearing will be close to a wingtip posi- tion. (Radials indicated by arrows are recommended, but you can use any combination you like, as long as your position is not beyond the VOR changeover point and the angle is not less than 30 degrees.)
When you tune and identify Bradford, place the desired radial (247) in the OBS and, when the CDI centers, you have reached VICKS intersection (maintaining the centerline of Victor 434 all the while, of course). Until you get to VICKS, the needle will remain to the right of center, so here’s the rule: When the “side” radial is set in the OBS, you have not arrived at the intersection as long as the CDI is deflected
Fig. 9-1 Navigational facilities forming the VICKS intersection. (Copyright Jeppesen Sanderson Inc., 1978, 1996; all rights reserved; not to be used for navigation)
116
toward the station, or to the right in this case. (Prove it to yourself;
before reaching VICKS, mentally stop the airplane and turn it to a heading of 247 degrees — you’d have to fly right to get to that radial.) If you had tuned Bradford and the needle came to rest on the side of the instrument away from the station (that is, to the left), better let Center know about it right away — you’ve passed VICKS.
And so to the fourth situation, the one you will use most fre- quently: figuring out the proper wind correction angle, or “bracketing the course.” If you always take immediate corrective action when you notice the CDI drifting off center, you’ll never get off course far enough to need bracketing; but a sharp turn over a VOR, or vectors to a new radial where the wind effect is unknown, may find you chasing a CDI that’s off-scale.
Assuming no knowledge of the wind direction or velocity, the first thing to do is turn 30 degrees toward the radial and wait for the nee- dle to center. For example, trying to track outbound on the 360 radial (Fig. 9-2), you find that a heading of 360 allows the airplane to drift to the right (CDI moving left). When a heading of 330 degrees puts you back on course, you have established the maximum “bracket” within which the correct heading lies — at 360, you cannot stay on course, and 330 will take you back to the radial. Now, cut the difference in half, turn to 345 degrees, and again watch the CDI. If it stays put, 345 is the correct heading. But if the needle starts to the left again, imme- diately turn to 330 — the heading you know will return you to course — and it won’t take nearly as long as the first time. Since 345 degrees has proved insufficient, take the next half step and turn to 340 degrees; be practical, accept the nearest 5-degree increment. Be- fore long, you’ll have a heading that will immobilize the CDI; this process works just as well in either direction.
This sounds like a terribly complicated, time-consuming process on paper, but in the air, it will take only a few minutes; as your ex- perience increases, you will be able to tell roughly how much cor- rection you’ll need by observing the rate at which the CDI moves. Your target is a dead-center needle all the time, which may explain why really good instrument pilots spend so much time checking their VOR receivers; the CDI remains so motionless, they have to make sure the set hasn’t failed!
No Ident? No Good
It stands to reason that the only stations that can be used for IFR en- route operations are those that are transmitting a usable signal. The
Chapter Nine
designers provided a built-in alarm system to alert you when a VOR fails, when it is shut down for maintenance, or when the signal qual- ity drops below a certain level. It’s a very simple scheme, consisting of either automatic or manual removal of the station’s Morse code identifier when any of these conditions exists. Your reaction should be equally uncomplicated: Whenever you tune a VOR and there’s no identifier, don’t use it! If an explanation of the outage isn’t printed on the chart nearby, let someone in ATC know of the problem. They’ll check their monitoring devices and take the appropriate action.
Distance-Measuring
Equipment
If your airplane is equipped with distance-measuring equipment (DME), you’ll probably have it turned on throughout the flight, so 118
Fig. 9-2 Bracketing a VOR course.
why not use it for identifying intersections? With the CDI centered, it’s merely a matter of flying along the radial until the charted num- ber of miles shows up on the DME indicator. Establishing yourself at an intersection with the help of DME is valid only when you use a station directly ahead or directly behind; authorized DME intersec- tions are shown on the Jeppesen charts by the letter D and on the government charts by an open arrowhead. (Check the chart legend for details.) The same ahead-or-behind limitation must be observed if you intend to derive accurate groundspeed readings from your distance-measuring equipment.
VOR Accuracy Checks
The odds are probably better than even that the next trip you fly IFR will be illegal, at least from a VOR receiver standpoint. Checking VORs is one of those things that almost all pilots know about, but somehow just don’t take the time to accomplish at the required intervals. Ac- cording to the book, you may not fly in the IFR system unless the VOR receivers have been checked for accuracy within the preceding 30 days. Furthermore, the pilot in command is ultimately responsible for making sure this requirement has been satisfied. It matters not whether you’re flying the same old airplane that you’ve owned for 10 years or the brand new Barnburner you rented for this one trip. You’re the pilot in command, and you’re the one the FAA will come looking for if they suspect a VOR malfunction is involved in a mishap. The way to stay current is to check the receivers on every flight. The system designers have made it easy for you by putting a ground test station (VOT) on most large airports and by designating certain spots on other fields where a nearby VOR signal can be received and used for testing. If time is running out and you are far away from either of these, there are designated airborne checkpoints, so there is no excuse for flying with VORs that have not been checked. Look in the Aeronautical Information Manual or Jeppesen’s “J-AID” for these facilities and checkpoints.
If all else fails, you may designate your own airborne check: Pick out a prominent landmark on an airway preferably 20 miles or more from the station and position the airplane directly overhead.
These situations should result in a centered CDI when the OBS shows the appropriate number (radial or course). Should you have to turn the OBS more than 4 degrees either way to center the needle for ground checks or more than 6 degrees either way for an airborne check, your set is out of tolerance, and IFR flight would be illegal.
Chapter Nine
Checking the VORs every time you fly is a fine habit to form, but all the effort and good intent will go for naught unless you make a record of what you have done. As soon as you have checked the receivers, make a note of the date, the location, the bearing error (how much you had to rotate the OBS to make the needle come to center), and affix your signature thereto. Where you maintain this record of VOR checks is immaterial, as long as you know where it is, because it’s one of the things the inspectors may ask for when they investigate an IFR incident. By making some kind of a VOR check before every IFR flight, you are effectively taking yourself off the hook.
There is another way you can accomplish this check, but it must be placed in the last-resort category; if no other means is available within the time limits (and that’s difficult to imagine because you can hardly fly for 30 days anywhere in the United States and not have been someplace where there was a VOR checkpoint), you may legally check one receiver against the other. Tuned to the same VOR, the OBS indications may not be more than 4 degrees apart with CDIs centered. But what if the first VOR is already 10 degrees off ? Treat this check as something you will do only if there’s no other way, and at the earliest opportunity, check the receivers properly.