Copyright 1999, Glenn Carlson, All Rights Reserved.
No reprints without permission form the Author.

Welcome fellow instructors. Last time we explored the concept
of three for one (or one for three, which ever way makes you
warm and fuzzy)  in planning your descent for landing. How
you descend to the runway and how you teach that descent
will make the difference between producing a safe and well
prepared instrument pilot or an accident waiting to happen.

With an ILS approach the decision to land is quite straight
forward. You descend to DH (DA) and if you have the
runway environment in sight and the prescribed weather
minimums you continue down the glide slope and land.

The non-precision approach is however not that easy. A
picture is worth a thousand words. Behold the Jepp.
Approach plate 11-2  LOC-2 RWY 16 Reno NV.

This approach plate has built in help in the form of a visual
descent point. As you know , not all plates show a visual
descent point but you can and should have your students
calculate a visual descent point and write it on the plate
for every approach that they plan to shoot. Now,
Captain you are boring me just a little! Hear me out it is
going to get better, much better, trust me ?

Let's look at the math in how the FAA figured out this
here visual descent point.  Minimums for this approach
take us down to 5700 feet msl which is 1288 feet agl. Ok,
round up to 1300 feet for easy math. Now look at the
distance from the visual descent point to the runway
threshold. It adds up to 3.8 miles. Hum 1300 times 3= 3900
or 3.9miles very close to 3.8 especially since we are using
rules of thumb here.

Your students have to have ingrained in their head that if
they fly this approach to minimums, which in this case is
1/2 mile from the threshold, they are not going to make it
to a landing. What you should be telling them is that although
the minimums for this approach are 6000 RVR unless they see
the runway environment by 3.8 miles they are not going to be
able to make "a normal descent to landing"

I teach that in a situation such as this with the visibility at say
3.8  miles or less to just plan on using circle to land minimums.
In this case the MDA is the same but as you know most of the
time this is not the case.
 

Also noteworthy on this approach plate is that the minimum
visibility for an aircraft using speeds of 140 knots or more must
have 2 1/2 to 3 miles visibility to land from this approach. I guarantee
you that if they don't get the field in site by the visual descent point
they will have no other choice but to circle to land. For a jet or other
high performance aircraft to try  and "chop and drop" to make it is
suicidal. The same goes for light aircraft as we shall  see .

In the real world, the visual descent point is your missed approach
point for a straight in approach. In recognition of this fact , many
approaches have the same MDA for straight in as well as circle….but
not always. Check out Reno 11-3  LOC DME 34.

No visual descent point but we can figure it out for ourselves. Straight
in minimums 653 feet agl times 3 call it 2000 or 2 miles. If the visibility
is not at least two miles , have your student plan on circling use an
MDA of 5340.

Once you get your student to analyze different approach plates and
realistically fly them in his or her head while preflight planning, the
safer pilot you will have made. I will leave you to look at two more
plates.Bullhead city, Ariz VORDME RWY 3 (VDP 18.1 DME) That's
5 miles from the runway. In VFR conditions fly straight in to a runway
and be 1700 feet AGL and now try and make the runway but start
down at 1 1/4 miles from the runway like the approach plate says. Let
your student do this with the hood off. Check out the necessary rate
of descent  to make it. Would you want your student to be in IFR
conditions and try make it. Think of the passengers ears and stomach
as he or she tries to make it.

My favorite one is one my last IFR student found in the Jepp. Manual.
Alturas, Calif NDB 16-1.1226 AGL minimums 1/2 mile from the runway.

Try that one in VFR conditions. In reality, one needs a good 3 1/2 miles
visibility to shoot this approach and make it straight in. If this airport is at
minimums, there is definitely NO straight in approach. And that, my fellow
instructors is the math you should teach. Have a good day.
From Capt. Carlson, over and out?

Link to Author's web site with information on some of his Books.