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equipment as a linear function of time as follows:
θ = (T0 – t) V/2
Chapter 3 Annex 10 — Aeronautical Communications
3-79 23/11/06
where:
θ = Azimuth or elevation guidance angle in degrees
t = Time separation in microseconds between TO and FRO beam centres
T0 = Time separation in microseconds between TO and FRO beam centres corresponding to zero degrees
V = Scan velocity scaling constant in degrees per microsecond.
3.11.4.5.1 The values of the angle guidance parameters shall be as shown in the following table:
Function
Maximum
scan angle
(degrees)
Value of t
for maximum
scan angle
(μs)
To
(μs)
V
(degrees/
μs)
Approach azimuth –62 to +62 13 000 6 800 0.020
High rate approach azimuth –42 to +42 9 000 4 800 0.020
Back azimuth –42 to +42 9 000 4 800 –0.020
Approach elevation –1.5 to +29.5 3 500 3 350 0.020
Flare elevation –2 to +10 3 200 2 800 0.010
Note 1.— Between the end of the TO scan and the beginning of the FRO scan there is a pause time of no radiation of
appropriate duration. Additional information is provided in Attachment G, 2.2.1.
Note 2.— The maximum scan angles shown recognize that the scan angle must exceed the proportional guidance sector
limit by at least one half of the width of the detected scanning beam envelope (in equivalent angle) to allow successful
decoding.
3.11.4.5.2 The tolerances on the ground equipment scanning beam velocity and the time separation between TO and
FRO pulses corresponding to zero degrees shall be sufficient to satisfy the accuracy requirements specified in 3.11.4.9.
3.11.4.5.3 The TO and FRO scan transmissions shall be symmetrically disposed about the mid-scan point listed in each
of Tables A-2 through A-5 of Appendix A. The mid-scan point and the centre of the time interval between the TO and FRO
scan transmissions shall coincide with a tolerance of plus or minus 10 microseconds.
3.11.4.6 Azimuth guidance functions
3.11.4.6.1 Each transmission of a guidance angle shall consist of a clockwise TO scan followed by a counterclockwise
FRO scan as viewed from above the antenna. For approach azimuth functions, increasing angle values shall be in the
direction of the TO scan. For the back azimuth functions, increasing angle values shall be in the direction of the FRO scan.
Note.— A diagram illustrating the scanning conventions is provided in Attachment G, 2.3.1.
3.11.4.6.2 Sector signals. The transmission format of any azimuth function shall include time slots for airborne antenna
selection, out-of-coverage indication, and test pulses as specified in Appendix A, Tables A-2 and A-3. The internal timing
accuracy of the sector signals shall conform to the internal timing accuracy of the DPSK transitions specified in 3.11.4.3.4.
Annex 10 — Aeronautical Communications Volume I
23/11/06 3-80
3.11.4.6.2.1 Ground equipment identification. The MLS providing services for a particular runway shall be identified
by a four-character alphabetic designator starting with the letter M. This designator less the first letter shall be transmitted
as a digital word as listed in Appendix A, Table A-7.
Note.— It is not required that MLS ground equipment will transmit identification outside the angle guidance coverage
sectors. If MLS channel identification is operationally required outside angle guidance coverage sectors, it may be derived
from associated omnidirectional DME. (See 3.11.5.5.2 and Attachment G, 8.2.)
3.11.4.6.2.1.1 The signal shall be transmitted on the data channel into the approach and back azimuth coverage regions.
3.11.4.6.2.1.2 The code bit in the time slot previously allocated for the alternate (Morse code) ground equipment
identification following the azimuth preamble shall be fixed in the “ZERO” state.
3.11.4.6.2.2 Airborne antenna selection signal. A signal for airborne antenna selection shall be transmitted as a “zero”
DPSK signal lasting for a six-bit period. The signal shall be available throughout the coverage sector in which approach or
back azimuth guidance is provided.
Note.— The signal provides an opportunity for the selection of the most appropriate antenna in a multiple antenna
airborne installation.
3.11.4.6.2.3 Azimuth out-of-coverage indication pulses. Where out-of-coverage indication pulses are used, they shall
be:
a) greater than any guidance signal in the out-of-coverage sector;
b) at least 5 dB less than the fly-left (fly-right) clearance level within the fly-left (fly-right) clearance sector; and
c) at least 5 dB less than the scanning beam level within the proportional coverage region.
The duration of each pulse measured at the half amplitude point shall be at least 100 microseconds, and the rise and fall times
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