CATIII operations. Go around below DH.
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Yup interesting, although those limits can be company ones too.
However you have to distinguish between the two different low vis 737 models available. Fail operational 737s can be operated down to no DH and 75m RVR in LAND3 (in which case an automatic rollout failure becomes interesting) and 125m RVR DH 50ft in LAND 2 (to use 125m you need a special approval and training scheme in place, otherwise its 200m). They have the higher crosswind limit of 25kts for normal operation and 20 kts for one engine out autolands. Fail passive ones do operate to the normal IIIa limits of 50ft DH and 200m RVR, max 20kts crosswind. As if that isn't enough Boeing offers the installation of a head up guidance system which allows manually flown CAT IIIa approaches, in fact the 737 classic was the first airliner which had that feature available although that wasn't widely known.
I do agree on the no go around once the reversers are selected and that is as far as i know a boeing recommendation as well. However balked landings are available if you have speedbrakes up as they autostow once you move the thrust levers up again, still i do not really want to test it. With a required visual segment of one element (one single light) of the runway lighting system for CAT IIIb rollout however it becomes quite challenging to continue a highspeed rollout manually after a failure of the rollout system.
Sorry for the OT though.
Really hope to see the AN-148 flying around europe, looks like a neat plane.
However you have to distinguish between the two different low vis 737 models available. Fail operational 737s can be operated down to no DH and 75m RVR in LAND3 (in which case an automatic rollout failure becomes interesting) and 125m RVR DH 50ft in LAND 2 (to use 125m you need a special approval and training scheme in place, otherwise its 200m). They have the higher crosswind limit of 25kts for normal operation and 20 kts for one engine out autolands. Fail passive ones do operate to the normal IIIa limits of 50ft DH and 200m RVR, max 20kts crosswind. As if that isn't enough Boeing offers the installation of a head up guidance system which allows manually flown CAT IIIa approaches, in fact the 737 classic was the first airliner which had that feature available although that wasn't widely known.
I do agree on the no go around once the reversers are selected and that is as far as i know a boeing recommendation as well. However balked landings are available if you have speedbrakes up as they autostow once you move the thrust levers up again, still i do not really want to test it. With a required visual segment of one element (one single light) of the runway lighting system for CAT IIIb rollout however it becomes quite challenging to continue a highspeed rollout manually after a failure of the rollout system.
Sorry for the OT though.
Really hope to see the AN-148 flying around europe, looks like a neat plane.
Are we talking about 140kt aeroplanes?
As for autoland capable no-HGS aeroplanes, I think that following autoland failure, manual landing has great chance of success down to 300m RVR. Below that, it's safer to go-around.
But that's just my opinion.
Clandestino has it about right.
With no fancy,optional extras such as huds,enhanced vision aids etc etc under EU Awops shooting a LVP approach,if there is any failure below 1000' aal then a MANUAL landing may not be carried out in 300m rvr or less.
As usual with these things there is a great get out clause along the lines of:
" unless the Captain is ABSOLUTELY certain a safe landing can be made a GO AROUND must BE CARRIED OUT in <300m vis"
ergo land safely...."well done"
screw it up even slightly ..." dont let the door hit your ar*e on the way out"
With no fancy,optional extras such as huds,enhanced vision aids etc etc under EU Awops shooting a LVP approach,if there is any failure below 1000' aal then a MANUAL landing may not be carried out in 300m rvr or less.
As usual with these things there is a great get out clause along the lines of:
" unless the Captain is ABSOLUTELY certain a safe landing can be made a GO AROUND must BE CARRIED OUT in <300m vis"
ergo land safely...."well done"
screw it up even slightly ..." dont let the door hit your ar*e on the way out"
If I interpret Denti’s operating limits correctly (#39), then LAND 2 may be part of a fail operational system (hybrid) enabling either continued autoland or reversion to manual landing with HUD. I would be surprised to learn if pure manual landings were authorised in RVRs below 200m for system failures below DH; a GA is normally mandated after any failure. There are many interpretations of operational clearances (including interpretations made by the regulators) – not all are valid.
Where a ‘super fail passive’ system enables an operation in RVRs below 200m, normally a GA is the mandated (regulator) procedure below DH, vs manual landing above 200m. I would tend to agree with Clandestino; not on the safety aspects of ability, but of having one consistent operating procedure for all RVRs.
However, my experience with these systems is that for the very few (and rare) failures below DH in RVRs less than 200m, the vast majority of the crews continued with a manual landing (against SOPs). The reasons given were very low altitude and judgement of the safest option – such is human performance.
Also, the majority of the failures involved ‘inadvertent’ autopilot disconnects caused by the crew’s tight grip on the controls. Other failures were due to ILS transmission failure or interruption. Thus there is need for appropriate crew training and adequate guarding of the autopilot disconnect button – a design issue.
Re the crosswind limits, these are usually hard limits published in the AFM (vice the more normal advisory max demonstrated) and result from the autoland certification. What many operators (and operational regulators) overlook is that humans have not been ‘certificated’ for manual landing in high crosswinds on a wet runway in low visibility.
Manual landing in 25 kts wet can be a demanding task in clear visibility, in fog it’s distinctly challenging. This area identifies a significant weakness in the regulations which require good crew judgement to apply lesser limits to their operation. Another good example is in blowing snow where there is a visual disorienting effect in additional to poor runway friction – laterally and longitudinal.
Autoland systems do not consider these aspects; it’s up to the crew, many of whom in my experience forget to attend to the ‘side’ issues of low vis operations when using automation.
There may be similar problems with HUD operations. The research quoted earlier evaluated development versions of HUD and noted “problems with division of attention” between symbology and the outside world, and “problems of presenting lateral guidance”, which perhaps indicate that HUD crosswind operations might have a lower margin of safety than normal operations – again good crew judgement is required.
Where a ‘super fail passive’ system enables an operation in RVRs below 200m, normally a GA is the mandated (regulator) procedure below DH, vs manual landing above 200m. I would tend to agree with Clandestino; not on the safety aspects of ability, but of having one consistent operating procedure for all RVRs.
However, my experience with these systems is that for the very few (and rare) failures below DH in RVRs less than 200m, the vast majority of the crews continued with a manual landing (against SOPs). The reasons given were very low altitude and judgement of the safest option – such is human performance.
Also, the majority of the failures involved ‘inadvertent’ autopilot disconnects caused by the crew’s tight grip on the controls. Other failures were due to ILS transmission failure or interruption. Thus there is need for appropriate crew training and adequate guarding of the autopilot disconnect button – a design issue.
Re the crosswind limits, these are usually hard limits published in the AFM (vice the more normal advisory max demonstrated) and result from the autoland certification. What many operators (and operational regulators) overlook is that humans have not been ‘certificated’ for manual landing in high crosswinds on a wet runway in low visibility.
Manual landing in 25 kts wet can be a demanding task in clear visibility, in fog it’s distinctly challenging. This area identifies a significant weakness in the regulations which require good crew judgement to apply lesser limits to their operation. Another good example is in blowing snow where there is a visual disorienting effect in additional to poor runway friction – laterally and longitudinal.
Autoland systems do not consider these aspects; it’s up to the crew, many of whom in my experience forget to attend to the ‘side’ issues of low vis operations when using automation.
There may be similar problems with HUD operations. The research quoted earlier evaluated development versions of HUD and noted “problems with division of attention” between symbology and the outside world, and “problems of presenting lateral guidance”, which perhaps indicate that HUD crosswind operations might have a lower margin of safety than normal operations – again good crew judgement is required.
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Correct, the cited limits for LAND2 are for a continued autoland. LAND2 is a degraded fail passive operation of the normally fail operational system. Automatic rollout and go-around capability is still provided. It is weird however that during normal (non degraded) one engine inoperative operation the system still announces LAND 3 (full fail operational system working) but only fail passive minimas may be used, this ties in with the lower crosswind limit of 20kts during one engine inoperative autolands.
Unfortunately we do not have HUDs in our current fleet so i can't really say if there is any SOP for continued manual landings in less than 200m RVR.
Unfortunately we do not have HUDs in our current fleet so i can't really say if there is any SOP for continued manual landings in less than 200m RVR.
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Bit of History
Denti: As if that isn't enough Boeing offers the installation of a head up guidance system which allows manually flown CAT IIIa approaches, in fact the 737 classic was the first airliner which had that feature available although that wasn't widely known.
Autoland gets you down in reduced vis; HUD lets you take off also. I don't think you'l find a pilot experienced with HUD who would prefer Autoland to HUD.
GB
