Jim Wilson writes:

 > So if you are 6 degrees or above you will get an inverted signal saying you
 > are too low and then at 9 degrees it suddenly acts like you are right on?  
 > Does that hold true right down to DH?
 > 
 > Oh my.  That *would* be interesting. :-)

You'd have to really screw up the approach for that to happen.

If you're being vectored for the approach, ATC will already have you
at the right altitude anyway.  If you're flying a full-procedure ILS
for real (extremely rare on an ILS approach, outside of training), you
will have to start the approach by descending to procedure-turn
altitude, which might be in the neighbourhood of 2000-2500 ft HAT
(height above touchdown), depending on terrain and traffic.  After
that, you intercept the LOC first, from (say) eight miles back, then
stay at PT altitude until you intercept the glidescope.

To get the false non-inverted reading, you'd have to be flying the
full procedure at about 7500 ft HAT (height above touchdown), and to
get the inverted one, you'd have to be at around 5000 ft HAT.  If you
cannot hold your altitude within several thousand feet on an approach,
the inverted signal will be the least of your problems (especially
when you're flying down to a decision height of 200 ft HAT).

Perhaps the problem comes when an airline pilot activates autoland too
early on a long, straight-in ILS, and the AP captures the false
signal.


All the best,


David

-- 
David Megginson, [EMAIL PROTECTED], http://www.megginson.com/

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