THE “THREE DEGREE” APPROACH

Acknowledgements: Thomas P. Turner (Mastery Flight Training Inc.)

Coming down final approach MAY look like it’s a lot steeper, but if you’re following the standard 3°glide-path, whether visually or following an instrument procedure’s vertical guidance, you are not very high above ground level as you near the runway. Draw the line and show the 3° glide-path to scale, and the angle and i very shallow indeed.

Some glide-paths and glideslopes are up to half a degree steeper, even more so in (charted) unusual cases. But even these steeper glide-paths result in heights not that much higher than the touchdown zone.

Just this week these new reports have appeared on the U.S. Federal Aviation Administration’s preliminary accident reporting website:
·       Cessna 172 on approach, struck a cable....
·       Cessna 210 landed short and slid onto the runway....
·       Rutan Long EZ landed short of the runway....
·       Waco UPF-7 stuck an approach light....

We’ve devoted many lessons to the need for proper airspeed, aircraft configuration, directional and glide-path control for landing. We’ve stressed the need to make a decision early if the airplane is not established on speed, in configuration, on glide-path, and in alignment with the runway before descending less than about 300 - 400 feet of the ground in light airplanes.

In real life I am not completely configured, on speed and may not be precisely on glide-path at the 300 - 400 AGL point in a visual approach - what I might call the outer visual gate. I will be in alignment with the runway, slightly above airspeed and perhaps above glide-path...with a trend toward final on speed, in configuration, on glide-path, and in alignment that will have me attaining all four targets as or before I reach the 100-foot AGL point, the inner visual or over-the-threshold gate.

If I’m not trending smoothly toward all of the target criteria when inside the outer visual gate, and not firmly on all targets passing through the over-the-threshold gate, then I follow the wise action: go around, evaluate options, and try again or divert to another runway (or airport) as conditions suggest.

An important reason to ensure we are on speed, in configuration, on glide-path, and in alignment with the runway on glide-path, is because even “on the beam” we do not have a lot of vertical space between our wheels and whatever might be beneath us. Remember, the standard approach glide-path assumes a uniform surface height from the runway along the final approach course - and that there are no trees, buildings, fences or SUVs there, either. Just a little low can be enough to get you featured in a YouTube video that continues to circulate years after the event!

If there’s a displaced threshold it’s there for a reason: to give you enough vertical space from obstacles while you’re on final approach. Sure, the pavement ahead of the displaced threshold is usable for take-off - obstacle clearance isn’t an issue - but that does not mean a “superior” pilot can ignore the displacement for landing. There simply isn’t enough clear vertical space.

Whatever you fly, stabilise your approach, trend toward and ensure you are on speed, in configuration, on glide-path, and in alignment with the runway on final approach; and remember that when you are on the proper glide-path you have a barely acceptable obstacle clearance, and very little margin for error beneath the glide-path guidance.

FLY SAFE!



Tony Birth