CAT IIIB no DH
Glueball: Thanks for your input. I knew about the surface radar coverage however are you so sure that the required fire service " response time" can be guaranteed under zero visibility conditions? Considering the size of some major airports and the thought of fire vehicles charging blindly towards an aircraft in trouble - do you really claim that the required level of fire coverage is still there in say less than 75m. vis?
My contention remains: is not the legal position not governed by the level of fire cover required to be active at the time of landing rather than the mechanics of the autoland?
Surely the 75m. minimum is not there just for the taxying of the aircraft after landing?
My contention remains: is not the legal position not governed by the level of fire cover required to be active at the time of landing rather than the mechanics of the autoland?
Surely the 75m. minimum is not there just for the taxying of the aircraft after landing?
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Hi MD83,
In euops area, If touch down RVR is below 200m you have to perform a cat3b approach. In cat 3b approach auto rollout is mandatory. Mid and stopend rvr must be at or above 75m.
I don't know on Boeing am but for airbus you can not use autorollout on contaminated rwy.
In euops area, If touch down RVR is below 200m you have to perform a cat3b approach. In cat 3b approach auto rollout is mandatory. Mid and stopend rvr must be at or above 75m.
I don't know on Boeing am but for airbus you can not use autorollout on contaminated rwy.
As one who was involved for Balpa in the technical discussions on Cat III RVR, I can confirm that the 75 metres was at the request of LHR fire service. They could not guarantee finding an aircraft in less.
Notice that - thanks to green taxi lead-ins and an excellent ground movement radar - taxi-ing (at LHR at least) was considered less of a problem. We also had lo-viz taxi charts with headings so that the FO could monitor progress.
Notice that - thanks to green taxi lead-ins and an excellent ground movement radar - taxi-ing (at LHR at least) was considered less of a problem. We also had lo-viz taxi charts with headings so that the FO could monitor progress.
Last edited by scotbill; 17th Dec 2011 at 14:44. Reason: typo
A long time ago I was involved with OPS/AFS trial to determine a practical minimum visibility for operations (BLEU Bedford). This involved a simulated off-the-side runway accident which was used to develop search techniques, communications, and the most suitable vehicles (seat height w.r.t. fog thickness/depth).
The results indicated that a met vis of 60m was an absolute practical minimum; it was assumed that surface radar would not available. This visibility translates into different RVRs depending on day/night and fog type. Thus a 75m limit seems very sensible.
Subsequently during an operation in 150m RVR night at GLA, the turn-round coffee-stop was marked by the absence of travelers, staff, and general hub-bub. This was explained by the met vis being between 40-60m and the bus system and taxis had all given up!
The results indicated that a met vis of 60m was an absolute practical minimum; it was assumed that surface radar would not available. This visibility translates into different RVRs depending on day/night and fog type. Thus a 75m limit seems very sensible.
Subsequently during an operation in 150m RVR night at GLA, the turn-round coffee-stop was marked by the absence of travelers, staff, and general hub-bub. This was explained by the met vis being between 40-60m and the bus system and taxis had all given up!
Scotbill: Thanks for that. That accords with what I remember from doing BALPA tech. work in the early `70s.
Still no-one on here seems to be able to come up with a definative answer as to what level of visibility fire services are assured and hence the legality of continuing to operate with RVRs below 75m.
(come on BOAC - you usually know these things!)
Still no-one on here seems to be able to come up with a definative answer as to what level of visibility fire services are assured and hence the legality of continuing to operate with RVRs below 75m.
(come on BOAC - you usually know these things!)
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michelda is correct, with less than 200m RVR you need an automatic rollout control or guidance system. However there are still distinctions between different systems and DHs, although all are considered CAT IIIb.
For example the 737 has only a fail passive automatic rollout system if one engine has failed above alert height (200ft). Therefore you need a DH now (50ft) and the minimum raises from 75m to 125m. Same if the autoland system reverts to LAND 2 status.
Autoland on contaminated runways is allowed, however boeing cautions that autorollout capability might not be enough to cope with correction demands. Pilots therefore have to prepared to disconnect the autoflight system and take over manually.
Personally i would only use it if there is no alternative left, as the above is a typical ass covering exercise and therefore if something does not work out as planned it all lands squarely at yours truly.
For example the 737 has only a fail passive automatic rollout system if one engine has failed above alert height (200ft). Therefore you need a DH now (50ft) and the minimum raises from 75m to 125m. Same if the autoland system reverts to LAND 2 status.
Autoland on contaminated runways is allowed, however boeing cautions that autorollout capability might not be enough to cope with correction demands. Pilots therefore have to prepared to disconnect the autoflight system and take over manually.
AFDS ROLLOUT mode performance cannot be assured when used on contaminated runways. The ROLLOUT mode relies on a combination of aerodynamic rudder control, nose wheel steering and main gear tracking to maintain the runway centerline using localizer signals for guidance. On a contaminated runway, nose wheel steering and main gear tracking effectiveness, and therefore airplane directional control capability, is reduced. To determine the maximum crosswind, use the most restrictive of the autoland crosswind limitation, or during low visibility approaches, the maximum crosswind authorized by the controlling regulatory agency.
CAUTION: If an autoland is accomplished on a contaminated runway, the pilot must be prepared to disengage the autopilot and take over manually should ROLLOUT directional control become inadequate.
CAUTION: If an autoland is accomplished on a contaminated runway, the pilot must be prepared to disengage the autopilot and take over manually should ROLLOUT directional control become inadequate.
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Meiklour
The problem is addressed the other way round. When LVP's are in force, the Fire Service are on "weather standby" at suitable places near the runway, rather than tucked up in their nice crew room.
I bet that makes them really look forward to fog!
The problem is addressed the other way round. When LVP's are in force, the Fire Service are on "weather standby" at suitable places near the runway, rather than tucked up in their nice crew room.
I bet that makes them really look forward to fog!
Last edited by BizJetJock; 17th Dec 2011 at 14:22. Reason: Spelling
I believe the 75m RVR limit was introduced as a consequence of the crash in thick fog of BEA Viscount G-AOHU on 7th Jan 1960 at LHR. A heavy landing collapsed the nose gear, causing the aircraft to catch fire as it slid down the runway. The fire service took about 30 mins to find the aircraft, by which time it had burned out. By great good fortune, no lives were lost. But as previous posters have alluded, it was accepted that 75m was a minimum acceptable for rescue operations. I once met a survivor of this accident whose description of the event was terrifying.
