Instrument Insights Part 6 of 12

Nonprecision Approaches

June 1, 1998

How to focus more attention on the procedure and less on the airplane

Nonprecision approaches can result in an accumulation of errors if not flown precisely. Descent planning alone can double a pilot's work load. Here are some ways to reduce distractions.

What if you had a five-speed transmission in your car but had to search through all the gears every time you went out on the highway? Pretty inefficient, right? Yet some pilots increase their work load during nonprecision approaches, as do some VFR pilots when landing and on final, because they don't know the configuration and power settings that give the desired performance.

There's a better way. Know in advance the power settings and configurations that provide the performance you need.

John Eckalbar, who preaches precise flying in his book Flying the Beech Bonanza (see " Pilot Briefing," April Pilot), suggests taking the power/configuration settings one step further by memorizing the pitch angle on the attitude indicator. For example, a Beech A36 Bonanza will fly 110 knots at 16 to 17 inches of manifold pressure with approach flaps down and a pitch angle on the attitude indicator of plus three degrees. (Much the same approach is described in Positive Flying by Robert L. Taylor and William M. Guinther.)

Determine configurations for takeoff (that's easy — full power and a pitch angle that gives best rate of climb), cruise climb, cruise, maneuvering, approach, descent, and short final. Determine power and configuration for unusual situations as well, such as when the controller asks you to keep the speed up on final. At some point on final, though, switch back to the normal power, speed, and configuration to avoid excessive floating. Helping the controllers has its limits.

Show some respect

Airline and corporate pilots generally avoid nonprecision approaches if possible. A corporate pilot who flies for a large food company in California says that he has not done an NDB approach in nearly five years. He admits that they were required more frequently in a previous job, flying a Learjet in Colorado.

His current business jet has a flight management system (FMS) that would literally fly a nonprecision approach for him, but he prefers not to use it.

"FMS has everything in the box, but we do so few NDB and nonprecision approaches that we don't trust the box," he said. Instead, the autopilot and heading bug are used for nonprecision approaches and descents.

His company recently considered prohibiting night circling approaches but realized that might eliminate full use of Teterboro Airport in New Jersey. An alternative under consideration was to increase the company's minimums for all nonprecision approaches, such as increasing visibility requirements by one-half mile.

Are nonprecision approaches all that dangerous? It would seem so, to hear corporate pilots talk. They can hardly be blamed; after all, your reward for a properly flown nonprecision approach at weather minimums is a scud run to the airport, followed by a rapid descent to a wet runway. It is commonly accepted that scud running is a dangerous business. The pressure on the pilot to cheat just a little and go below the minimum descent altitude, is enormous. That may be why some recent nonprecision approaches have ended up in the trees, as happened on a foggy night in Texas recently.

What the airlines do

Airlines have very specific procedures for nonprecision approaches. Here is some advice from an airline pilot who happens to be working part-time at AOPA headquarters.

  • Even though this type of approach contains the word nonprecision, it should be flown with absolute precision.
  • Have a well-defined procedure developed for each type of aircraft that you fly. The procedure should be designed to spread out or reduce work load so that the pilot can focus as much attention as possible on flying the aircraft, tracking the appropriate course, and leveling off at the appropriate altitudes. (Distractions, preoccupation, and high work loads are hazards for any pilot trying to fly an approach precisely.)
  • Focus on leveling off at the minimum descent altitude before beginning brief scans for the runway environment. It may help to put a sticker on the altimeter as a reminder of the MDA.
  • Pilots should not descend below MDA unless a visual landing can be accomplished at a normal rate of descent.
  • Airlines are more conservative in use of time or altitude than is allowed by the approach procedure. Our employee's particular airline starts the missed approach earlier, and maintains a higher altitude, than is required.

Such conservatism is understandable. "Airlines have killed many people [by] trying a nonprecision approach. Those types of approaches do require complete proficiency to be accomplished safely," the airline pilot said.

Views on getting down: fast or slow?

Experienced instrument flight instructors have suggested over the years that the descent to minimum descent altitude (MDA) be completed a half-mile to a mile before reaching the airport. That allows adequate time to search for the airport but minimizes exposure to low-altitude flight.

That's a great idea, but can you perform the mental calculations needed to determine the proper descent rate? If you fly nonprecision approaches on a daily basis, perhaps such mental dexterity is no challenge. Use the distance from the final approach fix to the airport (remember to subtract a half-mile to a mile) and the speed to make that calculation.

If that is too distracting, standardize on one descent rate that will get you down early enough on most approaches to search for the airport, yet limit your exposure to low-altitude flight.

An informal survey of instructors around the country shows that the descent rate taught most often falls between 700 to 800 feet per minute. Instructors interviewed are unanimous in recommending that pilots never exceed 1,000 fpm during the descent; it is too easy to descend below the MDA when using such a high rate. Memorize in advance the power and configuration settings needed for such a descent.

A word about GPS approaches

GPS offers the possibility that someday pilots may be led step-by-step through the twists and turns of a nonprecision approach, both laterally and vertically, with little to do but fly the airplane. Today's reality is that GPS nonprecision approaches are not that simple; in most cases, the problem stems from those GPS approaches that overlay existing VOR or NDB procedures.

Consider this example, one required by one of the more user-friendly GPS-capable panel units on the market. A pilot wants to make a GPS overlay approach to an airport that has the VOR on the field. Before reaching the VOR, the GPS must be placed in Hold mode; but the Hold button is actually labeled OBS. Once outbound, the pilot remains in Hold mode while tracking along a specific radial, and must remember to return to Approach mode when established inbound. Want to try calculating a descent rate while the GPS demands attention to its flashing Message light?

Here are some GPS tips to help you cope with the future. First, you must exert the same learning effort as when you bought the new home computer. Remember how it took hours to set it up properly and to read the 500-page manual? Think of your new GPS, either handheld or panel-mounted, as another home computer.

Obviously, you'll need dual instruction in VFR conditions before GPS approaches become second nature, the same as when you learned other types of approaches. One pilot finds that he forgets how to use the GPS if approaches are not made routinely, and he takes monthly dual instruction to relearn the box.

Lexicon

MDA — The lowest altitude, expressed in feet above mean sea level, to which descent is authorized on final approach or during circle-to-land maneuvering when executing a nonprecision approach.

Nonprecision approach — A standard instrument approach procedure in which no electronic glideslope is provided.

Tip Sheet

Art Holland, a flight instructor in the Chicago area, has not only an ATP certificate, but a Ph.D. in education. Here are his tips for VFR and IFR pilots alike, based on common student errors.

  • Use power to control altitude during the descent, whether descending to MDA or to the runway. Simply pitching the nose up to regain altitude causes a loss of airspeed and, shortly thereafter, a horrendous descent rate. Shoving the nose down causes excessive airspeed, throwing off the timing of the approach, and can lead to overshooting the touchdown point.
  • Keep your work load from interfering with aircraft control. If necessary, write down the radio frequency and enter it one digit at a time, looking back to the attitude indicator between digits. Or change the omni bearing selector a little at a time.
  • When you are in a turn, don't focus on anything else but the turn. Don't read approach plates; just do the turn. Otherwise, you are unlikely to feel the increased G forces resulting from a gradual steepening of the turn, and you may overbank.
  • Avoid the circling approach. If the tailwind is not strong, you may want to consider landing downwind rather than circling in scud.
  • If you are a VFR pilot and find yourself in the clouds, use very slight banks to make turns. Make half-standard-rate turns as shown on the turn coordinator. Look at the attitude indicator 90 percent of the time. If you need to climb or descend, very slight power changes will result in climb or descent. Use too great a power decrease and you'll risk setting up a rate of descent that you can't control.
  • Never go below the minimum descent altitude when on either a nonprecison or circling approach. Here are three reasons why you might get too low: Your altimeter may have an error; the altimeter setting might be from another airport where barometric pressure is different; few pilots can hold altitude exactly.