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You're high on the glideslope. How do you correct? Do you pitch down, or do you reduce power? If you want to start an argument, ask a group of pilots what they think. Pilots have debated for years whether it's better to pitch for airspeed and power for glideslope, or the other way around.
One of the most respected flying books ever written, Wolfgang Langewiesche's Stick and Rudder, lays out one of the most popular - and proven - ways to manage your aircraft: "pitch to speed, power to altitude." The book was written in 1944, and it holds true today.
But with technically advanced aircraft, things are changing. And they're changing because more aircraft than ever have flight directors and autopilots. So what's the difference when it comes to flying a glideslope? Let's look at both ways of flying it.
Most instructors (including us) have taught that when you're on a glideslope, you pitch for airspeed and power for altitude. It makes sense. If you trim your aircraft for a specific speed, you can hold that speed at any power setting without touching the flight controls, because trim holds airspeed.
Elevator trim keeps the aerodynamic forces acting on your elevator constant. And since a constant indicated airspeed creates a constant aerodynamic force on the tail, elevator trim will vary your pitch to hold that airspeed.
If you reduce power, trim will pitch the nose down and use gravity to make up for some of that lost thrust. And your airspeed will remain nearly constant if you let the nose move on its own. In fact - aircraft climb and descend because of excess power, not pitch attitude. If you have more power in than you need to to fly level at your trimmed airspeed, you'll climb. If you have less in, you'll descend.
So - if you find yourself low on glideslope, add some power and let the nose pitch up slightly.
And if you're high on glideslope, reduce power and you'll descend back on target.
The method works perfectly when you're flying without automation. But if you have a flight director, things change. Here's why.
If you're flying an ILS with a flight director, the flight director directs your pitch to stay on glideslope. But why?
Most flight director and autopilot systems can't control the throttle - they can only control the elevators, ailerons, and possibly the rudder. So, they have to control the aircraft using pitch and bank - without regard to power. If you're flying and ILS with an autopilot engaged, you'll control the power to manage your speed, and the flight director/autopilot will control your pitch and bank to stay on the glideslope and localizer.
As you fly the ILS, you'll follow the flight director's pitch commands to maintain the glideslope, and you'll set power to maintain your airspeed.
If you're low on the glideslope, the flight director will command you to pitch up. You'll need to increase power to keep from slowing down.
And, if you're high on glideslope, the flight director will command you to pitch down. You'll need to reduce power to keep from speeding up.
So what's the best method to fly a glideslope? In many ways, it's a combination of both.
Even though I almost always use a flight director now, I do practice non-automated, "raw data" approaches often. And when I fly without a flight director, I pitch for speed and power for glideslope. When I fly with automation, I pitch to match the command bars and power for speed.
But, in practice, pitch and power are always tied together. If I'm high on glideslope and I'm not slow, I pitch down and I reduce power. If I'm low and not fast, I pitch up and I add power. They work in concert. And while it's easier to get the hang of instrument flying when you tie one control to one action, realize that you never move anything - pitch or power - in isolation.
So what do you think? Would you pitch for airspeed and power for glideslope when you're flying without automation? What works best for you? Tell everyone about it in the comments.
Aleks is a Boldmethod co-founder and technical director. He's worked in safety and operations in the airline industry, and was a flight instructor and course manager for the University of North Dakota. You can reach him at firstname.lastname@example.org.