Tuesday, March 8, 2011
Perfect Your Approaches
Nonprecision suggests a casual approach to IFR procedures, but you’d best fly them with precision
Instrument flying was simpler then, or perhaps more difficult, depending upon your point of view. When the weather was down, IFR approaches demanded a combination of pilot skills and primitive radio-navigation aids. In those days, all instrument procedures were nonprecision. They were so imprecise, in fact, that many pilots invented their own techniques for landing "blind."
As one who had improvised as necessary to get the job done, Tom had less than glowing things to say about the old A-N radio ranges. Flying IFR by ear, with reference to an often confusing series of faint, barely audible Morse code dots and dashes, often masked by crashing static through an ill-fitting headset, was two parts skill, one part experience and at least one part blind, dumb luck. (The A-N range offered course guidance by broadcasting a Morse "A"—dit dah—when an airplane strayed left of course; an "N"—dah dit—when right of course; and a solid tone when on course.)
Then, there was the NDB approach. Radio beacons were used extensively as navigation and approach aids, and again, pilots often ad-libbed as necessary to get the job done, sometimes using commercial AM broadcast stations as homing fixes. ADF was better than the A-N range, but at best, the signal was only moderately reliable, and even the most accurate approach flown to an NDB, was a hit-or-miss operation.
Somehow, Tom Watson survived it all and died in bed a decade ago, though even he was a little amazed at his overall good fortune. Predictably, he regarded the current IFR system "almost too simple."
Yet, the primary point of general aviation is to go places and do things the airlines can't. We often operate to destinations outside the mainstream where there may be nonprecision procedures or none at all. Nonprecision approaches may be installed at airports where geographic obstructions or other ground obstacles make an ILS impossible. The ground-transmitting equipment for an NDB or VOR approach is a lot cheaper than for an ILS, and that can make it attractive to an airport operator.
A nonprecision approach can guide an aircraft to minimums as low as a 350-foot ceiling with ¾-mile visibility. NPAs also include localizer and VOR procedures that can provide reasonably accurate course reference to the airport but no vertical guidance.
The message is that the feds want a pilot to have a greater margin of error on a nonprecision approach. Without the benefit of a glideslope for vertical reference, the workload increases exponentially. Flying the airplane should always be Job One, but on an NPA, the pilot can feel overloaded with all the tasks necessary to find the ground.
A close examination of the approach plate is obviously the first requirement on any instrument approach, but it's even more essential during an NPA. You may have a choice of approaches, and you should be especially knowledgeable about the one that will serve you best so you can ask for it in case it isn't offered.
Most pilots regard a localizer as the optimum choice, followed by a VOR, an NDB and a DME arc at the bottom of the list. (Don't automatically disdain the back-course approach, by the way. It's true that reverse sensing is counterintuitive, but if your airplane is equipped with an HSI, you can simply set the front course heading on the OBS and fly the procedure with normal sensing.)
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Labels: Decision Making, Flight Training, Learning Center, Pilot Resources, Pilot Skills, Safety, Pilot Safety