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2 Answers

Flying the Glideslope

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Flight Instructor, Instrument Rating

Ok so maybe I have learned something incorrectly somewhere in my training.  I am studying for my CFII and recently was reading up about the ILS from the book "asa - The pilots manual instrument flying".   I came across the correct procedure to maintain glide slope as well the procedure for regaining the glide slope.  Change pitch attitude to regain glide slope and power for airspeed.  For Ex.  If above glide slope, lower pitch attitude slightly and adjust power to maintain airspeed.  What I was taught and was planning to teach is: Once the airplane is setup, trimmed and configured for an airspeed then it is simply reducing and managing power to achieve a rate of descent (Pitch for an airspeed and power for altitude).  If below the glide slope add some power to slow the rate of descent.  If above the glide slope reduce some power to increase the rate of descent to regain the glide slope.  The airspeed remains the same.  It seems like there is less to manage the way I planned on teaching it.  Adjust the power to maintain and find the correct descent rate (Ground speed x 5 = correct rate of descent). Anyone else teach it the way I learned?  Any comments or suggestions?

2 Answers

  1. Mark Kolber on Oct 05, 2013

    It’s really the old pitch vs. power technique argument dragged into instrument flight. And like the old silly argument, there is no “right” vs. “wrong.” Both work.

    Using pitch to control ILS glide path seems to be the more recent teaching trend for a simple reason. In light aircraft most of us have the ability to make tinier corrections with the yoke than with the throttle. In a trimmed airplane in a relatively stable atmosphere, it takes no more than slight pressure on the yoke to correct minor and temporary glide path deviations without any appreciable change in airspeed. Typically less than 5 KTS. We tend to be more ham-fisted with the throttle.

    So a lot of the teaching in recent years has been to make small corrections with the yoke and reserve throttle changes for more serious excursions.

    But I’d bet that there are plenty of pilots who will swear by using throttle and there’s nothing inherently wrong with either technique. There may even be aircraft where throttle changes work much better.

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  2. John D Collins on Oct 05, 2013

    As Mark points out both methods will work. However, if you use an autopilot, it will maintain the glidepath with pitch as all but the most sophisticated autopilots have no means of controlling power. In the big iron with autothrottles, the GS is still maintained with pitch and speed is maintained by the autothrottles. I personally think that continuous power changes is a relatively crude method to control the path on the GS and so I teach and fly a GS with pitch. In my Bonanza, I set a single power setting (15 inches MP) that through experience will give me my desired speed, if winds or aircraft weight end up with the speed being too high or low, I adjust the power about an inch of MP in the desired direction.

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