Tony leveled wrote:
>
> If the "glide slope" is at a height of 190 ft at a distance of 4 miles from
> the runway, I will put in a prayer for all the poor pilots relying on this
> ILS system hi hi.
Standard ILS glideslope is 3 degrees, but they vary. That angle is from
the ILS transmitter which is usually at or near the Runway Touch Down
Zone and not at the runway threshold, but that varies also.
200' probably put your tower just inside the LOW side of the glideslope
protection "funnel" (funnel would include the left/right indications of
the ILS also of course). Venturing beyond the protection of the ILS
low-side indications on an approach puts pilots beyond the point where
they should only venture if they like hitting things. But there are
crazy bastards who'll attempt to level off and "fly back onto the
glideslope from below" out there... they all have death-wishes, or an
innate inability to admit they screwed up and execute and immediate
climb and missed-approach procedures.
There are also so-called "non-precision" approaches which typically step
the pilot down using the pressure altimeter and some non-precision
directional information such as a Non-Directional Beacon (NDB) or GPS
coordinates, etc... you usually end up somewhere between 200' and 500'
AGL lollygagging around out near the approach end of the runway
somewhere, looking ahead for any signs of something that looks like an
airport.
Non-precision approaches attempt to get the aircraft down to the final
altitude 3-5 nautical miles from the runway environment to give the
pilot of a 200 knot aircraft a little bit longer to look out the window
for signs of an airport out there in the clouds...
4 miles isn't that far when you're doing 3 miles a minute! Even at a
more common speed of 120 knots, that's still 2 nautical miles a minute.
5 nm out at 120 knots gives you 2.5 minutes to play "Where's Waldo"
with the airport in a fog bank. Nautical miles are 6080' for those
interested... so your 4 statute miles is less than that in terms of
nautical miles, which is what pilots work in. 3.4 nautical miles to be
exact.
Most missed approach points for precision approaches like ILS are
somewhere before the runway. Many non-precision approach missed
approach points are in the center of the runway environment and many are
based on speed and a stopwatch, if the navigation transmitter isn't on
the airfield.
And now I've bored you all to death with just the tip of the iceberg
when it comes to instrument flying... and I've probably screwed some of
it up, but it gives the flavor from the other side of the cockpit
glass/plexiglass.
To be fair to us radio folks, I've seen FAA drop non-precision
approaches to an airport entirely after the construction of a tower
nearby -- they sometimes determine the tower is more useful than the
non-precision instrument approach. It's a tough juggling act they have.
Keep those towers lit and painted!!! AND THANK YOU!!!
We folks in our gas-powered flying bugsmashers appreciate it greatly
when the WX goes down the tubes unexpectedly! (GRIN)
Nate WY0X
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