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!