On Instruments: Riding the rails

Sounds busy, doesn’t it? And tense, too, if you’re facing low instrument meteorological conditions. This is definitely not the time to be chasing needles, or sawing away at the power controls to nail those evasive approach speeds and descent rates. What you want are nice, gradual changes in airspeed, descent rate, and configuration as you make your way from initial approach fix to runway threshold. As for course tracking, big-screen displays can help you anticipate turns—but you’ll still need a fast, efficient scan to keep the balancing act under control.

This is where the stabilized approach concept comes into play. The FAA has one definition for a stabilized approach, but corporate, charter, or airline operators may develop their own operational guidelines. Whatever the method, here are some key qualities of a stabilized approach. Perform a missed approach or go-around if any of these conditions are not met below 1,000 feet above the airport elevation (under IFR) or 500 feet above airport elevation (under VFR):

• Checklists complete.
• Airplane in correct landing configuration.
• Correct power setting for configuration.
• Airspeed no less than the speed recommended for VREF/short final.
• Airspeed no greater than VREF/short final airspeed plus 10 knots.
• Sink rate no more than 1,000 feet per minute.
• On the final approach course, CDI and glideslope needle deviations no greater than one dot.
• Only small corrections in pitch and heading to maintain the published flight path.
• On circling approaches, wings must be level when the airplane approaches 300 feet above the airport elevation.

It’s those second and third requirements—correct configuration and power setting—that are of key importance. You’re well ahead of the game if you know the combination of power setting, landing gear, and flap deflection needed to produce a given airspeed and descent rate. You can determine these with a little practice.

For example, during one training session in a Cessna Turbo 210 I did some experimenting and came up with the following:

• On precision approach final approach course with gear down, a power setting of 16 inches manifold pressure and 2,400 rpm, with 10 degrees of flaps and a 3- to 5-degree nose-down pitch attitude (one bar-width down on the attitude indicator’s pitch indicator) yielded a 500-fpm descent rate at 100 knots.
• On nonprecision final approach segments with gear down, 14 inches of manifold pressure, 2,400 rpm, and 5 degrees nose-down pitch attitude (one to two bar widths) produced an 800-fpm descent rate at 100 knots. If “diving and driving” in level flight to the missed approach point, 20 inches/2,400 rpm/3 degrees nose-up attitude created a 100-knot, level-flight condition.

If you haven’t done so already, you can find out the specific variables for the airplane you fly by doing your own experiments. Just adhere to any advice in the pilot’s operating handbook, and bear in mind that power and pitch will vary according to weight.

When you fly down final in this steady-state mode, you’re free to concentrate on tracking the inbound course and making the critical visual transition to a landing instead of making constant power changes. And compensating with pitch trim for each change.

There are other benefits to making constant-airspeed, constant-descent approaches. Any sudden changes in airspeed or vertical speed serve as wind-shear alerts. Being trimmed for approach airspeed means minimal pitch changes when it’s time to flare for the landing. Maintaining a constant flap setting does the same thing: putting down a final flap deflection prior to landing in low instrument weather can cause you to balloon back up into the overcast and force a missed approach.

Some will argue that light airplanes can safely make large power and configuration changes when flying down final. Maybe, maybe not. In visual conditions you may get away with this. But during instrument approaches in actual conditions, trying to “save” an unstable approach sometimes ends up with flying too fast down final, landing long, and running off the end of the runway. Better to power up, pitch up, fly a missed approach or go around, and start over again if you see your trip down final falling apart.

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