by Charles Gulick
Like a Pro to SFO
Chart: San Francisco
Title: 115.8 INT R103
En Route Coordinates:
Aircraft: N17371, E4980
Tower: N17340.023, E5060.0702
Tower: 10/60 (Indefinite)
Time: Day (Dusk or Night optional)
Special Requirements: Tune NAV 1 to 115.8 and set OBS to R103
Here's a picturesque approach to San Francisco International, paralleling a right base along the Pacific coastline. The title reminds you of two specific things you must do in this scenario:
Tune NAV 1 to the San Francisco VOR, on a frequency of 115.80.
Set your OBS to radial 103, which you'll intercept and track to SFO (airport code, obviously, for San Francisco International).
This will set you up to execute a nice professional final approach.
The idea is to continue on your present heading while keeping a peeled eye on your OBI needle. After a few minutes, it will start moving toward the center of the instrument. When it does, observe the rate at which it moves--a rough analog of your distance from the station. The movement in this case is fairly rapid because you're only a dozen miles DME from your destination. Because you're crossing the radials rapidly, you'll want to start your turn to intercept R103 accordingly--that is, a few degrees ahead of the point where the needle will move to center.
Try to estimate this, and make your right turn to 103 degrees so you reach that heading just as the needle moves to center. Then fly the needle, which means do whatever you have to do to keep the OBI centered. The trick is to turn to-ward any deviation; that is, if the needle is to the right of center, yaw right a degree or two, if the needle is to the left of center, yaw left. When the needle is again centered, yaw to the heading indicated by the radial you're tracking, in this case 103 degrees. If that heading results in a "slippage" of the needle left or right, make a one-degree correction left or right. Your heading may not always agree exactly with the radial number; it could be a degree or so lower or higher. Accept such situations. As long as your compass heading and your selected radial are within a degree or so of agreement, fly the needle, regardless of what exact heading results. Keep the needle centered.
This tracking a VOR radial to a station is the primary means by which pilots the world over navigate from one section of a country to another, and finally to any destination airport. You could do this, using solely your instrument panel, if you had no outside references at all: no horizon, no landscape, no sky. You could do it in black of night, or socked in in an overcast. You don't have to know the names of towns, the lie of rivers, the destinations of highways, or anything else about the geography below you. All you need to know is the frequency of the VOR station to which you want to fly, and that your NAV radio is tuned to that frequency, that the radial you wish to track, and your present heading, are in virtual agreement, and that you're keeping the needle centered. Know those things, and you can navigate confidently to any-where in the world you want to fly.
In the present case, radial 103 will point you straight to Runway 10 Left at San Francisco International, almost as accurately as would an ILS approach. The difference is that you have to decide what rate of descent, what "glideslope" will be required to touch down just beyond the runway threshold. (Your glideslope needle may become activated as in an ILS approach, but don't rely on it for this landing. Rely on your eyes.)
Enjoy your somewhat "classic" arrival at SFO.