by Richard Morey, CFII
As you gain experience as a flight instructor, you realize that there is no one way to fly a particular approach, but rather a number of ways to accomplish the same thing. You also develop a technique you teach which works both for you and your students. In my mind nothing is gained by making things more complicated than they need to be. Keep it simple and there is less to go wrong.
One of the greater challenges of instrument flying is the Instrument Landing System (ILS) approach. Dealing with both vertical and lateral guidance requires good multitasking abilities, instrument scan and a light touch on the controls. It helps to have a good grasp of the basics. Here are my tips on shooting one “down to minimums.”
Set Up Approach Level
Set the aircraft up prior to localizer and glide slope intercept. This means having your power and trim set for level flight and instrument approach speed. Using a Cessna 172SP as an example, a power setting of about 2050 RPM in level flight results in about 90 knots airspeed.
Using a more complex aircraft as an example, in a Cessna 182RG, 20 inches of manifold pressure, 2300 RPM, 10 degrees of flaps and gear down will give you 100 knots when trimmed for level flight. Both of these speeds are fast enough to keep controllers happy, yet slow enough to bleed off speed for landing once the runway is in sight.
Set the aircraft up for approach level when you feel you want to slow things down. On a full approach, I suggest students set approach level after the procedure turn. On a vectored approach, once the turn to “base” is given (right angle to the final approach course), I feel it is time to go to approach level. As your comfort level increases, you can delay slowing to approach level until a mile or so outside of glide slope intercept. Remember, we learn the basics so we can eventually go beyond the basics. Use what works for you!
To Step Down or Not To Step Down?
Many ILS approaches have a step down once you are established on the localizer. On the ILS 18 to Madison, Wisconsin (MSN), you may, once established and cleared, descend from 3000 ft. to 2500 ft. You now have a choice, ether decrease power, descend 500 ft., add power and level off, or simply hold 3000 ft., continue tracking the localizer and start your descent at glide slope intercept. Which one keeps things simpler? If you are flying a localizer-only approach, do the step down, but for an ILS, do one power reduction and make life simpler.
Holding The Glide Slope
The real advantage of having set up approach level early is not simply to slow things down, but to make it easier to establish a descent that holds the glide slope. Again, using a 172SP as an example, at glide slope intercept, reduce power to Precision Approach setting, about 1800 RPM. This should result in a 450-500 feet per minute (fpm) descent at a bit over 90 knots, without having to adjust trim! This will hold the glide slope if your groundspeed is in the 90-100 knot range. If you leave your hands off the control yoke and fly with rudder, you will see the Vertical Speed Indicator go to well below -500 fpm, then recover to almost 0 fpm, then go down, etc. After about three oscillations the aircraft will stabilize at -500 fpm. You can dampen the oscillations by watching the Vertical Speed Indicator (while continuing the scan), and giving a bit of backpressure once the Vertical Speed Indicator gets to -500 fpm. The Vertical Speed Indicator will then reverse itself. Give the yoke a bit of forward pressure when the Vertical Speed Indicator shows a descent of less than -500 fpm. This should stabilize your descent rate. If you have not determined what power settings you need for Approach Level and a Precision Approach, do so in visual conditions. This will make all aspects of your instrument flying simpler.
Ground Speed Times Five
If you have a way of determining your ground speed such as a GPS or DME, you have an advantage when flying an ILS. Take the ground speed and multiply it by five. This will give you an approximate descent rate in feet per minute you need to hold the glide slope. If the headwind puts your ground speed at 80 knots, then you will need to hold -400 fpm to stay on the glide slope (80 X 5 = 400). In our 172SP, this means reducing power to 1850 RPM or so instead of 1800. If you have a tailwind, you will have to reduce power to less than 1800.
Without a direct ground speed read out, you have to do a bit of guessing. If at your Precision Approach power setting you are consistently below the glide slope, then you have a headwind and need to add a bit of power. If consistently above glide slope, then you need to reduce power a bit. Keep in mind that wind direction and velocity will change as you descend.
Hug The Bug
If you have a heading “bug” on your Directional Gyro, you can use it to your advantage by setting it slightly to the upwind side of your inbound course. This will remind you which side of the inbound course your wind correction should be. Once inside the final approach fix, your corrections should be within 10 degrees of this heading bug. Thus, “hug the bug.”
The Vertical Speed Indicator Is Your Friend
For all corrections of descent rate, use your Vertical Speed Indicator. For small corrections on the glide slope, keep your descent rate adjustments to within 200 fpm either side of the determined descent rate. This will avoid overcorrecting.
For example, if you find yourself at half deflection low on the glide slope, add just enough back pressure to the yoke to reduce your descent rate from its target -500 fpm to -400 fpm or at most -300 fpm. Hold this until you are again on glide slope, then relax the back pressure and allow the aircraft to continue descending at -500 fpm.
The Last 500 Feet
As you get closer to the runway, you also get closer to the localizer and glide slope antennas. The result is, as we get closer, the indicators get more sensitive. The last 500 feet require a different type of scan, and a lighter touch on the controls. The trend of the course deviation and glide slope indicators (needles) becomes more important than simply their position. If you are indicating below glide slope, but the needle is moving towards center, you need to put in a slight bit of forward pressure on the yoke. If you wait until the indicator is centered to add forward pressure, you will be above the glide slope before the correction takes effect. This is the same for the localizer. Consider using the rudder only for slight course corrections. You have to lead the needles to get the desired results. The closer you are to decision height, the more this is true.
Landing
Once the runway is in sight, reduce power further, add flaps when airspeed allows and make a normal landing. Many instrument students feel uncomfortable coming over the threshold at a high rate of speed. This is something they need to get use to. Adding flaps or reducing power to slow down while trying to hold glide slope is difficult at best, and unnecessary.
In Summary
By using the aircraft’s natural aerodynamic properties to get the desired result, the smart pilot can minimize his/her workload. In level flight, every power setting has an associated airspeed. By reducing that power setting, a descent rate will be established at a bit greater airspeed than level flight (T tails will hold the same airspeed). By taking advantage of this, and knowing “the numbers,” a smart pilot can minimize workload and maximize the likelihood of a good outcome. This is not the only way to fly, but in my experience, it is a good way!
Editor’s Note: Richard Morey is a Certified Instrument Flight Instructor (CFII), owner of Morey Airplane Company, and manager of Middleton Municipal Airport-Morey Field, Middleton, Wis.
