Near miss with 5 airliners waiting for T/O on taxiway "C" in SFO!
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The design was set around 1979, so what was available then to crunch the numbers?
Today, some vendors are hitting limits with a 20 meg database in world-wide subscriptions.
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I was speaking of the newest version of the FMC is a 486, the highest memory option is 1GB.
20M memory, Yes, with all of these coded procedures coming about, the navdatabases are having to get pared down. Getting pretty creative with waypoint naming, the usual nomenclature out the window.
The FMS for the smaller aircraft, with the Garmins and such, are far more powerful with up to date electronics.
20M memory, Yes, with all of these coded procedures coming about, the navdatabases are having to get pared down. Getting pretty creative with waypoint naming, the usual nomenclature out the window.
The FMS for the smaller aircraft, with the Garmins and such, are far more powerful with up to date electronics.
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Someone made the decision that computers for safety critical systems had to be 'formally proved' by mathematics. This was difficult but just about achievable with 'simple' 286 chips with a single core and nothing really clever in its operation. However, with multicore CPUs which are effectively a set of computers working together all dropping and picking up threads of programs, pre-fetching expected code branches based on algorithms, being pre-empted and picking up a new thread etc etc., formal proof becomes impossible or at least an nP problem. Certification testing is going to have to change as it makes no sense to restrict the capability of the CPU in the FMC in this way.
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It has already been a factor. E.g., the Comair 5191 wrong runway takeoff crash at LEX.
Due to his schedule the controller was working alone after sleeping only 2 hours in the past 24. And the crash occurred on the "wrong side" of the controller's circadian rhythm -- he would normally be asleep at the time.
Since he was alone, the controller cleared Comair 5191 for takeoff before the aircraft had reached the intended runway and then attended other workload (administrative tasks) at the tower. That was a missed opportunity to notice that the aircraft had lined up on the wrong runway.
Due to his schedule the controller was working alone after sleeping only 2 hours in the past 24. And the crash occurred on the "wrong side" of the controller's circadian rhythm -- he would normally be asleep at the time.
Since he was alone, the controller cleared Comair 5191 for takeoff before the aircraft had reached the intended runway and then attended other workload (administrative tasks) at the tower. That was a missed opportunity to notice that the aircraft had lined up on the wrong runway.
@zionstrat2
but the fms seems to be not flexible enough to accommodate it properly according to this post
http://www.pprune.org/rumours-news/5...ml#post9829103
but the fms seems to be not flexible enough to accommodate it properly according to this post
http://www.pprune.org/rumours-news/5...ml#post9829103
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I think that is a little unfair on the controller at Lexington. The two thresholds were effectively in the same place viewed from the tower. The flight crew chose an unlit GA runway rather than the lit main runway. Visibility over airports at night is confusing at the best of times. By the time the controller could have recognized that the aircraft was attempting takeoff on the short runway he could have said nothing to prevent the accident.
The controller further stated that it might have been possible for him to detect that the accident airplane was on the wrong runway if he had been looking out the tower cab window. ...
The concurrent radar and tower tasks that required the controller to divide his attention occurred during the window of opportunity when the controller could have, but did not, notice that the airplane was stopped short of runway 26.
After the controller transferred control of American Eagle flight 882 to the Indianapolis ARTCC, he did not have any further active radar duties. However, after the transfer, the controller performed an administrative task—the traffic count—instead of monitoring the departure of Comair flight 5191. The controller had turned around in the tower cab to perform this task before the start of the critical window. At that time, the airplane had not yet deviated from the issued clearances. However, at the end of the critical window, the airplane had accelerated beyond the maximum airspeed that would have allowed the airplane to remain on the available runway if the flight crew rejected the takeoff and used maximum braking.
Thus, at that point, the controller missed his final opportunity to notice the flight crew’s error in enough time to take action to prevent the accident.
The concurrent radar and tower tasks that required the controller to divide his attention occurred during the window of opportunity when the controller could have, but did not, notice that the airplane was stopped short of runway 26.
After the controller transferred control of American Eagle flight 882 to the Indianapolis ARTCC, he did not have any further active radar duties. However, after the transfer, the controller performed an administrative task—the traffic count—instead of monitoring the departure of Comair flight 5191. The controller had turned around in the tower cab to perform this task before the start of the critical window. At that time, the airplane had not yet deviated from the issued clearances. However, at the end of the critical window, the airplane had accelerated beyond the maximum airspeed that would have allowed the airplane to remain on the available runway if the flight crew rejected the takeoff and used maximum braking.
Thus, at that point, the controller missed his final opportunity to notice the flight crew’s error in enough time to take action to prevent the accident.
After the accident, FAA increased staffing at LEX, hiring four additional controllers. It will be interesting to know the staffing levels at SFO at the time of this incident.
We have now had 39 pages of wheat and chaff.
I am still incredulous that two grown men cannot safely fly a visual approach at night to a well-lit runway in good weather conditions without creating 39 pages of wheat and chaff on pprune.
I am still incredulous that two grown men cannot safely fly a visual approach at night to a well-lit runway in good weather conditions without creating 39 pages of wheat and chaff on pprune.
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Someone made the decision that computers for safety critical systems had to be 'formally proved' by mathematics. This was difficult but just about achievable with 'simple' 286 chips with a single core and nothing really clever in its operation. However, with multicore CPUs which are effectively a set of computers working together all dropping and picking up threads of programs, pre-fetching expected code branches based on algorithms, being pre-empted and picking up a new thread etc etc., formal proof becomes impossible or at least an nP problem. Certification testing is going to have to change as it makes no sense to restrict the capability of the CPU in the FMC in this way.
It is way harder to have a formally-proven system because quite a bit of what is taken for granted in most computer gear is not allowed because it can't be reliably modelled.
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On the controllers shortages at SFO , I do not have the exact figures but Nationwide it is between 15 and 20% , mostly compensated by overtime . NATCA has an interesting piece on the US controller shortage on their web site : http://www.natca.org/
But as to the question : Would an extra controller had spotted the deviation earlier ?
I frankly do not think it would have made any difference in this case , but that is only my opinion.
The total number of fully certified professional controllers (CPCs) has dropped 10 percent since 2011 and continues to decline. The most recent FAA count indicates there are 10,532 CPCs. This number represents both a 28-year low and the disturbing continuation of a sharp five-year decline. The lack of a stable, predictable funding stream has made these problems worse. Despite some incremental progress since late 2015, the current total of CPCs is more than 2,300 short of the FAA’s overall operational target of 12,896.
I frankly do not think it would have made any difference in this case , but that is only my opinion.
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But as to the question : Would an extra controller had spotted the deviation earlier ?
It does seem an odd situation whereby people are asking if a second ATC controller, positioned at the side of an approach, at night, could have a better visual appreciation that a 2 man crew could be lined up, visually, on to the wrong runway.
It does seem an odd situation whereby people are asking if a second ATC controller, positioned at the side of an approach, at night, could have a better visual appreciation that a 2 man crew could be lined up, visually, on to the wrong runway.
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I still don't understand is why the United crew didn't say "AC, go around you're on the taxi way"?! It was clear that ATC didn't noticed it. With that, I'm surprised that ATC didn't see what was going on. Same thing with the Asiana who was below the glide at final. Do they have such old equipment that they can't see it?
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It does seem an odd situation whereby people are asking if a second ATC controller, positioned at the side of an approach, at night, could have a better visual appreciation that a 2 man crew could be lined up, visually, on to the wrong runway.
When pilots make errors, we want to give controllers the best chance to detect them so corrections can be made. Likewise when controllers make errors, pilots should also have the awareness and tools to detect and correct them.
I find it odd that the layered approach to safety is so difficult for many to understand. The 'Swiss cheese' model has been around for awhile now.
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^^ Nothing wrong with that, but I think wingview's point may have been that since the two-person "layer" didn't work for the AC crew, there's no certainty that two ATCs further removed from the scene would have worked any better. That's the way I read it, anyway.
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The controller certainly seems to share neither blame nor responsibility.
That said, with hindsight, they did give an unhelpful and mechanical response to an obviously confused arriving aircraft.
From the evidence presented here, I choose to believe that a less busy controller could have added more value, suggesting to me at least that controller staffing levels or workload may be a contributory factor.
That said, with hindsight, they did give an unhelpful and mechanical response to an obviously confused arriving aircraft.
From the evidence presented here, I choose to believe that a less busy controller could have added more value, suggesting to me at least that controller staffing levels or workload may be a contributory factor.
Last edited by pilot9249; 12th Aug 2017 at 00:22.
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The only realistic contributing factor at LEX was the messed up taxiway configuration. (Long since resolved.)
The crew caused this crashed by:
1. Not checking their EHSI magnetic heading against the runway heading for reasonableness.
2. Taking off on an unlighted runway without so much as a question.
3. Far too much extraneous conversation during taxi out.
Also, pre flight of the wrong airplane.
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How many checks and balances?
The controller was already there, and in his own judgement, if he wasn't doing other tasks he might have been able to detect that the aircraft was lined up on the wrong runway.
Why not support him by:
- Not putting him on a schedule resulting in 2 hours of sleep in 24 hours on the backside of his circadian rhythm
- Making available a second controller to share his workload, per FAA guidelines
- Giving him time & space to observe critical phases of flight, instead of doing admin tasks
- Providing additional tools / technology to detect wrong runway incursions
49 people perished on that crash. If another set of eyeballs had a chance to prevent the accident, why not take advantage of that?
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But as to the question : Would an extra controller had spotted the deviation earlier ?
I frankly do not think it would have made any difference in this case , but that is only my opinion.
I frankly do not think it would have made any difference in this case , but that is only my opinion.
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I asked my wife, a recently retired controller of the Tower/Tracon variety, if she had any comments after reading the preliminary stuff from the NTSB that was posted many pages ago.
Her third comment was that aircraft lining up with taxiways happens a whole lot more often than you hear about.
Her second comment, which directly addresses the post above, was that it is really difficult from the controller's position in the tower to identify exactly which stretch of pavement an aircraft is lined up with.
Her first comment, addresses workload--at the time this was all unfolding, just before the hour, the lone controller might very well have been cutting a fresh ATIS, in addition to everything else.
FWIW.
Her third comment was that aircraft lining up with taxiways happens a whole lot more often than you hear about.
Her second comment, which directly addresses the post above, was that it is really difficult from the controller's position in the tower to identify exactly which stretch of pavement an aircraft is lined up with.
Her first comment, addresses workload--at the time this was all unfolding, just before the hour, the lone controller might very well have been cutting a fresh ATIS, in addition to everything else.
FWIW.