Hilton wrote:
OK, since we're never going to agree on this, please help me out
here. I'm
a CFI-I. If I were to have a lesson with a student who is pretty much ready
for his IR checkride tomorrow morning, please write out the math that he/she
would need to do in IMC on the ILS when his/her glideslope failed. I would
need to convince this student that doing this math in IMC (while doing all
the other stuff) is easy/safer/better than starting the timer.

Let's assume that the GS fails at 2700' (MSL), the DH is at 357' (MSL), a 3
degree glideslope, an 'ILS' airspeed of 100 knots, a climb airspeed of 80
knots. For simplicity, let's assume no wind conditions.

Thanks.

Hilton


I don't think I'd want to teach students that when your original idea of
starting the timing at the FAF is much better. At least with the
numbers you used in the example, you'd still be on the other side of the
non-precision FAF at most airports, since you're over 7 miles out at
2700'. They try to keep FAFs within 6 miles so they don't have to add an
"excessive length of final" penalty to the LOC MDA.
What would be bad is if after successfully making the calculations, the
student realized that they forgot to start the timer when they went
missed approach, so now they have to add the guesswork of how far they
flew between MA initiation and completing the calculations.

John