"Peter R." wrote in message
...
Gary Drescher wrote:

Except that he'd received and acknowledged a low-altitude alert. If his
GS
needle *didn't* show he was very low, then he knew something was wrong
either with the GS or with the controller's radar.

Not at all suggesting that this was the case, but at our local flight
school that has all late model C172SPs equipped with B/K KLN-94 GPS's and
moving maps, a number of students over the last few years have been known
to forget to toggle the NAV/GPS switch from GPS to NAV when transitioning
from en route to ILS approach.

As you know, when this happens the VOR1 instrument would show the CDI
alive
(but really tracking the GPS's course for the localizer). The glideslope
needle, however, would be flagged and remain perfectly centered, as if the
pilot were flying a perfect glideslope.

Yup. Fortunately, there are at least five ways for an instrument pilot to
detect that problem before it's too late: 1) double-check the NAV/GPS
switch; 2) observe the flag on the GS; 3) the GS needle should start high
and then come to center when approaching the FAF; 4) even when established
on the GS, a needle that stays perfectly centered at all times should arouse
suspicion; 5) a low-altitude alert should certainly call attention to the
problem.

--Gary