Jim wrote:

wrote:

On Mar 11, 8:09 pm, Sam Spade wrote:

wrote:

On Mar 11, 5:10 pm, Sam Spade wrote:

No glide slope for a LOC appraoch :-) to determine DH.

There is a timing table to determine the LOC MAP.

But of course you do know that the timing table is based on GS. What
if your GS was 68 knots Sam?
DME is your ONLY source to ensure that you are at MAP along WITH
timing. If you want to descend below MDA based on time alone AND no
DME, I sure wouldn't want to fly with you.

Of course I do NOT know that. The timing table is for the LOC MAP. DA
is your MAP for the ILS.

This newsgroup is so lacking in the fundamentals.


You imply Sam that timing alone is how you determine the MAP. I say
it's not.

DME determines when you can go below MDA which would be at MAP not 3
minutes 12 seconds.

Be my guest on descending below MDA at 3:12 without DME Sam. I won't
be in the plane with you as you come up short or even overshoot the
MAP due to headwinds or tailwind considerations.


Please correct me if I'm wrong as I'm just working on my instrument
rating. On a localizer approach you never descend below MDA unless you
have the airport environment in sight. Timing is not required on an
ILS, but it's a good idea to start the timer anyway in case you lose the
glide slope (out of action, not too high/low) and have to revert to a
localizer approach. You never descend below the DH on an ILS unless you
have the airport environment in sight. MAP is determined by being on
glide slope and at DH. Cruising down the glide slope at 68 is just fine
as long as you stay on the glide slope. ("Just fine" may vary depending
on who is behind you.) The timer (not required) will expire, but DH is
determined by altitude, not time or DME anyway?

But I'm with the OP in wondering why DME is required. Timing seems to
work for most other localizer approaches to determine MAP, all the
intersections and the missed approach holding points are determined by
VOR radials.

The DME requirement is most likely an error. The FAA designers make
plenty of mistakes.