Instrument Flying: Basic and Advanced, Special Edition Page: II

                                
Foreword

Instrument approach procedures on the radio ranges
are limited to let downs through the overcast, provided
ceiling and visibility are above a relatively high mini-
mum. The aircraft must proceed to an alternate airport
whenever the ceiling and/or visibility is lower than
the approved minimum for this type of operation.
Special installations are required to provide the pilot,
in flight, with accurate directional guidance along the
landing flight path when landing under lower mini-
mums becomes necessary. These radio landing aids
must guide the pilot through the overcast on a line of
flight which will bring the aircraft to a landing on
the near end of the runway under conditions of zero/
zero visibility and ceiling.
The original Army Landing System, employing two
portable radio transmitters emitting a signal on 201
kilocycles and 219 kilocycles respectively, now known
as the Modified A-1 System, can be successfully used
to guide the pilot below a 250-foot overcast into a posi-
tion whence a contact landing straight ahead is prac-
tical. The one great advantage of this system is that
no equipment need be installed in the aircraft in
addition to the Left-Right Radio Compass or the
Automatic Radio Compass already available. It is not
a true landing system because the flight path of the
ii                                              RES

aircraft cannot be controlled accurately enough to bring
the aircraft onto a runway.
The foregoing installations are being currently
superseded by the complete "Localizer-Glidepath" in-
stallations, which are described in detail under Section
III. The earlier equipments are also covered herein,
because the Modified A-1 system is still in operation
and use, and because the Runway Localizer installation
is a component part of the complete system. The Lo-
calizer-Glidepath employs the ultra high frequency
fan markers, the runway localizer and the glidepath
transmitters. The position of the aircraft is shown
with respect to the runway approach line by the Blue/
Yellow indications of the pilot's localizer indicator
(1-101-C) and with respect to the glide path approach
by the horizontal needle of the same indicator. This
glidepath is projected, from a point a short distance
from the approach end of the runway to be used, at
an angle 2 to 2.50 above the horizontal.
The British Standard Beam Approach System, also
known as the Lorenz, renders let downs to minimum
ceilings of 100-foot practical. A detailed discussion of
the flight procedures in use with the British Standard
Beam Approach System has been published for the
information of the Service in T.O. No. 30-100E-1.

TRICTED

RESTRICTED
T. O. No. 30-100F-1
FORE WORD

0

w

3