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Let:
a1 + a2 + a3 + a4 + a5 + a6 + a7 = 5 540 hours
s1 = 20 hours
f1 = 2½ hours
f2 = 6¼ hours
f3 = 3¾ hours
f4 = 5 hours
f5 = 2½ hours
Specified operating time = 5 580 hours
MTBF = ANctuumalb oepr eorfa tfianiglu triems e
=
7
1
1
5
i
a
= Σ
= 5 554 0 = 1 108 hours
ATT F-5 23/11/06
Annex 10 — Aeronautical Communications Volume I
A = AcStpueacl iofipeedr aotpinegra ttiimnge t×im 1e0 0
=
7
i
1
7 5
i 1 i
1 1
a 100
a s f
i
i i
=
= =
×
+ +
Σ
Σ Σ
= 55 554800 × 100 = 99.3 per cent
___________________
23/11/06 ATT F-6
ATTACHMENT G. INFORMATION AND MATERIAL FOR GUIDANCE
IN THE APPLICATION OF THE MLS STANDARDS
AND RECOMMENDED PRACTICES
1. Definitions
(see also Chapter 3, 3.11.1)
Dynamic side-lobe level. The level that is exceeded 3 per cent of the time by the scanning antenna far field radiation pattern
exclusive of the main beam as measured at the function scan rate using a 26 kHz beam envelope video filter. The 3 per
cent level is determined by the ratio of the side-lobe duration which exceeds the specified level to the total scan duration.
Effective side-lobe level. That level of scanning beam side lobe which in a specified multipath environment results in a
particular guidance angle error.
MLS point D. A point 2.5 m (8 ft) above the runway centre line and 900 m (3 000 ft) from the threshold in the direction of
the azimuth antenna.
MLS point E. A point 2.5 m (8 ft) above the runway centre line and 600 m (2 000 ft) from the stop end of the runway in the
direction of the threshold.
Standard receiver. The airborne receiver model assumed in partitioning the MLS error budgets. The salient characteristics
are: (1) signal processing based on the measurement of beam centres; (2) negligible centring error; (3) control motion
noise (CMN) less than or equal to the values contained in Chapter 3, 3.11.6.1.1.2; (4) a 26 kHz bandwidth 2-pole low
pass beam envelope filter; and (5) angle data output filtering by a single pole, low pass filter with a corner frequency of
10 radians per second.
2. Signal-in-space characteristics — angle and data functions
2.1 Signal format organization
2.1.1 The signal format is based on time-division multiplexing wherein each angle guidance function is transmitted in
sequence and all are transmitted on the same radio frequency. The angle information is derived by measuring the time
difference between the successive passes of highly directive, unmodulated fan beams. Functions may be transmitted in any
order. Recommended time slots are provided for the approach azimuth, approach elevation, flare, and back azimuth angle
functions. Preceding each scanning beam and data transmission is a preamble which is radiated throughout the coverage
volume by a sector antenna. The preamble identifies the next scan function and also synchronizes the airborne receiver signal
processing circuits and logic.
2.1.2 In addition to the angle scan function, there are basic and auxiliary data functions, each with its own preamble,
which are also transmitted from the sector antennas. The preamble permits each function to be recognized and processed
independently. Consequently, functions can be added to or deleted from the ground configurations without affecting the
ANNEX 10 — VOLUME I ATT G-1 23/11/06
Annex 10 — Aeronautical Communications Volume I
23/11/06 ATT G-2
operation of the receiver. The codes used in the preamble and data functions are modulated by differential phase shift keying
(DPSK).
2.1.2.1 DPSK data signal characteristics. The DPSK data are transmitted by differential phase modulation of the radio
frequency carrier with relative phase states of 0 or 180 degrees. The DPSK data signal has the following characteristics:
data rate — 15.625 kHz
bit length — 64 microseconds
logic “0” — no phase transition
logic “1” — phase transition
2.1.3 Examples of the angle function organization and timing are shown in Figures G-1 and G-2.* Details and
definitions of the data items shown in Figure G-1 are given in Chapter 3, 3.11.4.8.
2.1.4 The sequences of angle guidance and data transmissions shown in Figures G-3A, G-3B and G-3C have been
demonstrated to provide sufficient freedom from synchronous interference.
2.1.4.1 The structure of these sequences is intended to provide sufficient randomization to preclude synchronous
interference such as may be caused by propeller rotation effects.
2.1.4.2 The sequence pair shown in Figure G-3A accommodates the transmission of all functions. Any function not
　
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