With the local izer captured, and outside the normal glideslope
capture limits, the PFD will annunciate the following
modes at
this time:
● LOC in green.
● GS in white.
Any other vertical mode in use at this time will also be
displayed.
As the aircraft approaches the glideslope beam, the vertical
beam sensor
(VBS) monitors TAS, vertical speed, and glideslope
deviation in determining the correct capture point. At
glideslope capture, the computer drops any other vertical mode
that was in use, and automatically generates a pitch command to
smoothly track the glideslope beam.
At this time, the PFDwill annunciate:
. LOC in green
. A green GS that is boxed for 5 seconds to emphasize that the
capture phase has occurred.
The glideslope deviation signal is routed to the symbol
generator from the navigation receiver on the ARINC 429 bus.
From the symbol generator, the signal is routed to the FZ-820
Flight Guidance Computer through the ASCB.
Gain programming is performed on the glideslope signal to
compensate for the aircraft closing on the glideslope
transmitter, and beam convergence caused by the directional
properties of the glideslope antenna. Glideslope programming
is normally accomplished as a function of radio altitude and
vertical speed.
The radio altitude signal is rate limited,
summed with vertical speed, and limited again before gain
programming the glideslope signal. If the radio altimeter is
not valid, then GS gain programming is accomplished as a
function of preset height above runway estimates and run down
as a function of true airspeed.
From the GS gain programming
block, the glideslope signal is filtered, rate limited and
summed with estimated vertical deviation rate.
Estimated vertical deviation rate is used as a damping term to
help maintain a truer track of the glideslope beam. The
estimator utilizes normal acceleration provided from the IRS,
along with glideslope deviation, to provide an inertially
derived vertical rate, with long term glideslope deviation
correction.
22-14-00
Page 298.118
Aug 15/91
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