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T
L = Theodolite corrected sample of course/path bends (microamperes)
M = Mean value of course/path bends (microamperes)
T = Region to be evaluated (± 20 seconds wide)
± 2 = Maximum bend amplitude specification at point K (microamperes)
t , t , t , ... = Time intervals that noise exceeds allowable 2 value.
For the facility to be acceptable in this region:
100 [T – (t + t + t . . .)] 95%
N
1 2 3 N
1 2 3
+ 2 N
– 2 N
t1 t3
t2 t4
T2
K
L
M
Zero reference — A
T
Figure C-2. Evaluation of course/path bend amplitude
ATT C-5 23/11/06
Annex 10 — Aeronautical Communications Volume I
The 95 per cent maximum amplitude specification is the allowable percentage of total time interval in which the course/path
bend amplitude must be less than the amount specified in Figure C-1 for the region being evaluated. Figure C-2 presents a
typical example of the method that can be employed to evaluate the course/path bend amplitude at a particular facility. If the
sum of the time intervals t1, t2, t3, where the given specification is exceeded, is equal to or less than 5 per cent of the total time
T, the region that is being evaluated is acceptable. Therefore:
T – [(t1 + t2 + ...)]
100
T
≥ 95%
Analysis of ILS glide path bends should be made using as a datum the mean glide path and not the downward extended
straight line. The extent of curvature is governed by the offset displacement of the ground equipment glide path antenna
system, the distance of this antenna system from the threshold, and the relative heights of the ground along the final
approach route and at the glide path site (see 2.4).
2.1.7 Owing to the complex frequency components present in the ILS beam bend structures, measured values of beam
bends are dependent on the frequency response of the airborne receiving and recording equipment. It is intended that beam
bend measurements be obtained by using a total time constant (in seconds) for the receiver DDM output circuits and
associated recording equipment of 92.6/V, where V is the velocity in km/h of the aircraft or ground vehicle as appropriate.
2.1.8 Monitor systems. Available evidence indicates that performance stability within the limits defined in Chapter 3,
3.1.3.6, 3.1.3.7 and 3.1.5.6, i.e. well within the monitor limit, can readily be achieved.
The choice of monitor limits is based on judgement, backed by knowledge of the safety requirements for the category of
operation. However, the specifications of such monitoring limits do not indicate the magnitude of the normal day-to-day
variations in performance which result from setting-up errors and equipment drift. It is necessary to investigate and take
corrective action if the day-to-day performance frequently drifts beyond the limits specified in Chapter 3, 3.1.3.6, 3.1.3.7 and
3.1.5.6. The causes of such drifts should be eliminated:
a) to reduce greatly the possibility of critical signal parameters hovering near the specified monitor limits;
b) to ensure a high continuity of ILS service.
Following are some general guidelines for the design, operation and maintenance of monitor systems to meet the
requirements in Chapter 3, 3.1.3.11 and 3.1.5.7.
1) Great care should be exercised to ensure that monitor systems respond to all those variations of the ground facility
which adversely affect the operation of the airborne system during ILS approach.
2) Monitor systems should not react to local conditions which do not affect the navigational information as seen by
airborne systems.
3) Drifts of the monitor system equipment should not appreciably reduce or increase the monitoring limits specified.
4) Special care must be taken in the design and operation of the monitor system with the aim of ensuring that the
navigational components will be removed or radiation cease in the event of a failure of the monitor system itself.
5) Some monitors rely on devices which sample the signal in the vicinity of the transmitter antenna system. Experience
has shown that such monitor systems require special attention in the following aspects:
23/11/06 ATT C-6
Attachment C Annex 10 — Aeronautical Communications
a) where large-aperture antenna systems are used, it is often not possible to place the monitor sensors in such a
position that the phase relationship observed in the far field on the course exists at the sensing point.
Nevertheless, the monitor system should also detect antenna and associated feeder system changes which
significantly affect the course in the far field;
b) changes in effective ground level caused by snow, flooding, etc., may affect glide path monitor systems, and the
actual course in space differently, particularly when reliance is placed on the ground plane to form the desired
　
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