5.8.3 RVR MEASUREMENT REPORTS
ICAO recommends that RVR reports are given with 50m increments when the RVRis less than 800m and 25m increments when the RVR is less 150m. In any case, any change of the RVR value must be known by the ATC as soon as possible and in less than 15 seconds.
During operations, the pilot must know the RVR value related to the touch-down.Generally, it is not necessary to give the other values (MID, stop-end) unless these values are lower than the TDZ report or there is special mention in the ATC procedures.
Figure 5.8 Two types of transmissometer
Transmitter and receiver

5.9 AERODROME MAINTENANCE
5.9.1 INTRODUCTION
A system of maintenance for visual aids must be established at an aerodrome to ensure both lighting and marking system reliability. A system of maintenance for ILS installations must also be established with regular ground and flight checks as mentioned in the ICAO Annex 10.
5.9.2 LIGHTING SYSTEM CONDITION
As it is difficult to have at any moment in time zero failures in the lighting system, ICAO recommends that in any event, the percentage of unserviceable lights during a CAT II or CAT III approach should not exceed the values shown in the table of figure 5.9.
Figure 5.9
5%  in the approach lighting system from the threshold to 450m before the threshold 
5%  in the runway centerline lights 
5%  in the runway threshold lights 
5%  in the runway edge lights 
10%  in the touchdown zone lights 
15%  in the approach lighting system from the point 450m before the threshold and beyond 
25%  in the runway end lights 

However, to preserve the pattern of the lighting system, it is also recommended to ensure that two unserviceable lights are never adjacent (except in the same crossbar or barrette where two adjacent unserviceable lights are permitted).
To check the pattern of the lighting system aerodrome maintenance services can either use a photograph of the complete system, taken at night or use automatic lighting system reports.
5.9.3 SECONDARY POWER SUPPLY FOR VISUAL AIDS
A secondary power supply for visual aids is required with maximum switch-over time as indicated in ICAO Annex 14 and shown in the table of figure 5.10.
Figure 5.10
Maximum switch-over time 
1 second  15 seconds 
* Approach lighting system * Runway threshold * Runway end * Runway centerline * Runway touchdown zone * Stop bars at taxi-holding positions (CAT II) * All stop bars (CAT III)  * Runway edge * Essential taxiway including stop bars other than those at taxi-holding positions (CAT II) 

5.9.4 ILS MAINTENANCE
ILS installations must be ground- and flight-checked at regular intervals in accordance with the requirements of ICAO Annex 10. Moreover, users must be advised as soon as possible, and according the ATC procedures, of any degradations in ILS performance.
　
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