Tuesday, August 9, 2011
Making Sense Of The Back-Course Approach
They’re the words every instrument pilot dreads: “Cleared for the back-course approach”
Right up front, it's important to acknowledge that pilots flying behind HSIs have an advantage on back-course approaches. All the old analog HSIs and the current crop of digital, glass-panel-equipped airplanes, whether Garmin, Avidyne, Aspen, Sandel or some other manufacturer, have made BC approaches less of a problem. You simply set the front course heading under the pointer, and all will be forgiven. The OBS will deliver proper sensing with left for left and right for right.
In the case of the aforementioned Orange County approach, you'd simply set the front-course localizer heading of 193 degrees on the HSI, and fly the 013 degree radial just as if it was a front-course localizer. Corrections would all be normal, i.e. in the direction of needle deflection.
You might think experienced pilots could easily force their brains to overcome the puzzle of reverse sensing. Not necessarily. A large accumulation of hours doesn't immunize pilots to the confusion of BC. Years ago, a retired U.S. Navy fighter pilot was flying his Bonanza into Monterey, Calif., in hazy VFR conditions, and decided to simply track the back course to the proximity of the airport from the southwest until he was in close, then join the normal pattern. Like most of us, he had read about back-course approaches but never actually flown one. After a confusing series of S-turns, he gave up and followed the coastline to Monterey.
You might think experienced pilots could easily force their brains to overcome the puzzle of reverse sensing. Not necessarily.Some pilots who must fly BC approaches on a regular basis claim that a rote technique serves them as well or better than any other method. I was first exposed to that philosophy in amphibious seaplane training at the Lake Aircraft facility in Tomball, Texas. We were taught to say out loud, "This is a water landing—the wheels are up," or "This is a land landing—the wheels are down." The theory was/is that it's difficult to ignore your own voice suggesting the proper action. (The philosophy is somewhat analogous to a memory trick for remembering someone's name. Use a weird voice and shout it out loud, preferably when there's no one around, to call the guys in white coats.)
Accordingly, pilots faced with an off-course deviation during a back-course approach may say out loud, "The needle is left, fly right," or "The needle is right, fly left," or words to that effect.
IFR minimums for back-course approaches typically are about the same as for circling approaches following a precision ILS. At Orange County, ILS minimums on 19R were 200-feet ceiling and 2,400-feet RVR with all approach facilities working. Switch to a localizer with the glideslope generator inop, and minimums became 408 feet and 2,400 RVR. Convert the approach to a circling, however, and minimums rose to 600 and a mile. In this case, VOR and NDB minimums were the same as the bottom numbers for the back course at Orange County.
That won't always be the case. Terrain and noise considerations may dictate a higher minimum for a back course than the other approaches.
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