"JimBob" wrote in message
oups.com...
It's conceivable that the GS was giving a false reading without
flagging

Is there a way you can check the GS reading?

A few ways. One check, of course, is to determine that the ILS is properly
IDed and the GS is not flagged. You can also check that the GS needle
actually moves (if you're so precise a pilot that it's staying at dead
center, you can deliberately deviate slightly to confirm its
responsiveness). When you cross the FAF at GS altitude, you should check the
altimeter against the expected altitude as indicated on the profile; past
the FAF, you can check the altimeter against the expected altitude for your
distance from the FAF (as measured by markers, DME, or other fixes if
available, or just by dead reckoning). Third, if the controller's radar
shows your altitude, you can get an altitude alert (as the HPN pilots did).
These checks assume the GS needle isn't fully deflected (past the FAF); if
it is, you should be executing a missed approach whether the GS is working
or not.

--Gary