SECTION 3: CHAPTER 3 RVR Flashcards
The RVR system has been evolved to make available a more localised assessment of visual range in relation to a particular runway when the meteorological report gives a visibility of
less than 1500 metres.
The RVR indicates the range over which the pilot of an aircraft on the centreline of a runway can expect to see the runway surface markings, the lights delineating the runway or identifying its centreline.
The two methods of RVR assessment available at suitably equipped aerodromes are:
(1) Instrumented RVR, using electronic equipment;
(2) Human Observer Method.
The UK standard for reporting RVR extends from zero to 1500 metres in the following steps:
1) 0 to 400 metres in 25 metre steps
(2) 400 to 800 metres in 50 metre steps
(3) 800 to 1500 metres in 100 metre steps.
Note that any observed value, which does not fit the reporting scale, shall be rounded down to the nearest step lower in the scale. It is recommended that 50 metres be regarded as the lower limit and 1500 metres be regarded as the upper limit for assessments of RVR
Outside of these limits, reports should indicate that RVR is less than 50 metres or more than 1500 metres.
Instrumented RVR (IRVR)
- 1 This method gives an automatic and continuous display of RVR values to ATC.
- 2 Transmissometers are used to measure atmospheric opacity from fixed points alongside a runway, the number of units in any system being determined by the category of the ILS or MLS installation and runway length. In a three transmissometer system the units are linked by an associated data transfer system to a central processor. The processor computes the RVR for each transmissometer position and displays it in digital form to ATC.
The three transmissometers are located one at each end of the runway adjacent to the touchdown zone and the third near the runway mid- point area. For RTF transmission purposes the locations will be known as “Touchdown”, “Mid-Point” and “Stop End” and RVR values will relate to these positions.
The system automatically allows for runway edge light intensity settings but the DEO is to be informed if a controller has reason to believe that
the runway lighting is not operating at the selected level. Additionally the DEO is to be informed if a pilot reports actual conditions which are significantly different from those being indicated by IRVR methods.
Duration of Assessment
5.1 IRVR reporting to aircraft is started:
(1) whenever the aerodrome meteorological report shows the visibility to be less than 1500 metres;
(2) whenever the IRVR display is indicating an RVR value equal to or less than the maximum for that system;
(3) whenever shallow fog is reported and during a period for which it is forecast.
A number of different IRVR systems are installed at UK aerodromes. The processors in some systems are programmed to automatically reduce in intensity, or suppress, the display of the mid-point and/or stop-end readings when the values are not operationally significant.
Unless a suppressed value is specifically requested by a pilot, the RVR reports transmitted are to contain only those values that are displayed at full intensity. The value of the touchdown position is always displayed at full intensity and if no other values are at full intensity this is the only value which needs to be passed.
IRVR values are to be passed to aircraft at
the beginning of each approach for landing and, thereafter, whenever there is a significant change in the RVR until the aircraft have landed. A significant change is defined as a change in value of one increment or more. The current RVR value is also to be passed to aircraft before take-off.
Even though a pilot may have received an IRVR value from the ATIS broadcast, controllers must ensure that they pass the current value as specified above.
7.3 When all three positions are to be reported to the pilot, they are to be passed as three numbers relating to touchdown, mid-point and stop end respectively, e.g.
“RVR runway (designator) 650 — 500 — 550 metres”.
7.4 If only two values are to be passed, they are to be individually identified, e.g.
“RVR runway (designator) Touchdown 650 — Stop End 550 metres”.
7.5 A high degree of priority should be given to such broadcasts to ensure that current RVR information is provided to pilots with the minimum delay.
Transmissometer Unserviceability
8.1 If the touchdown transmissometer fails, the IRVR system may still be serviceable provided that confirmation is received from the DEO to this effect
In such circumstances the mid-point value is to be used to determine the ATC procedure and is to be passed to the pilot together with the stop end value, if this is available. It is imperative that the pilot should be informed that the touchdown transmissometer has failed, e.g.
“RVR runway (designator) Touchdown not available — Mid-Point 600
— Stop End 400 metres”.
If two transmissometers become unserviceable
the RVR value for the remaining instrument provided that it is not the stop end value, may be used. If the RVR value for the stop end is the only one available, the system is to be regarded as unserviceable for that runway. By changing the direction of use of the runway it may become serviceable again with the single available value representing the touchdown reading
When the IRVR system is unserviceable, controllers should revert to
Human Observer RVR where provided, or to the reported meteorological visibility to determine ATC procedures. In the latter case, pilots should be passed the reported meteorological visibility and advised that the IRVR system has failed.
Occasionally pilots of aircraft may report, or observations from the aerodrome control tower may indicate, that the visibility conditions on the runway are significantly different to those being reported.
Under no circumstances is a controller to pass a pilot information which suggests that the visibility is better than the RVR reported, whether assessed by IRVR or a human observer. However, when a pilot’s report or an observation from the aerodrome control tower indicates a worse condition on the runway, this information is to be passed with subsequent RVR reports for as long as the condition is considered to exist according to the phraseology in CAP 413
Intensity Setting
10B.1 All RVR observations, including those for transmission in meteorological reports, are to be made with the runway edge lights set at the intensity appropriate to the prevailing conditions.
However with some IRVR equipment, because of the design of the system, transmissometer readings may only be displayed when the runway lights are set at an intensity of 10% or more. Settings less than 10% may result in all three readings being replaced by zeros. If, during RVR conditions, a pilot requests a reduced runway edge light setting of less than 10%, he is to be advised that an RVR reading may not be available at this setting.
