Asiana 777 Crash at SFO
06-29-2014, 09:59 PM
#951
Da Hudge
Joined APC: Oct 2006
Position: Poodle Whisperer
Posts: 17,473
Originally Posted by Airhoss
80Kts,
Just for clarification sake here on the Bus incident
How did he "disable" the low speed protection?
Answer;
He did disable the low speed protection but he didn't know that he had disabled it due to a lack of system understanding. He had the auto thrust system engaged and he had the throttles in the CL detent which means that the airplane should be in managed or selected speed mode IE auto thrust will maintain a selected FCP speed or a programed managed speed from the FMC. And the auto thrust system will maintain that speed, unless you get below a certain radar altitude then the airplane will not maintain speed or thrust as it thinks you want to land. It's been a long time since I flew the bus but it's somewhere around 100 AGL where the airplane starts switching to land mode and there are several other things that happen as you get lower.
So he set the the FCP speed to the speed he wanted for the pass then descended below the that critical radar altitude which made the airplane think he was going to land so the power started to come back for landing. By the time he figured it out and manually pushed the throttles to TOGA it was too late.
All he ever had to do was disconnect the auto thrust system and manually fly the throttles which is what he should have been doing during a low pass in any case. You can disconnect the throttles by simply pushing them to the TOGA detent or you can hit the disconnect switches on the throttles or push the A/THR button on the FCP any one of those actions gives you manual throttles and then they work just like any conventional throttles you've ever used.
I am a bit rusty on A-320 system details but that is pretty darn close to how it happened and why.
Just for clarification sake here on the Bus incident
How did he "disable" the low speed protection?
Answer;
He did disable the low speed protection but he didn't know that he had disabled it due to a lack of system understanding. He had the auto thrust system engaged and he had the throttles in the CL detent which means that the airplane should be in managed or selected speed mode IE auto thrust will maintain a selected FCP speed or a programed managed speed from the FMC. And the auto thrust system will maintain that speed, unless you get below a certain radar altitude then the airplane will not maintain speed or thrust as it thinks you want to land. It's been a long time since I flew the bus but it's somewhere around 100 AGL where the airplane starts switching to land mode and there are several other things that happen as you get lower.
So he set the the FCP speed to the speed he wanted for the pass then descended below the that critical radar altitude which made the airplane think he was going to land so the power started to come back for landing. By the time he figured it out and manually pushed the throttles to TOGA it was too late.
All he ever had to do was disconnect the auto thrust system and manually fly the throttles which is what he should have been doing during a low pass in any case. You can disconnect the throttles by simply pushing them to the TOGA detent or you can hit the disconnect switches on the throttles or push the A/THR button on the FCP any one of those actions gives you manual throttles and then they work just like any conventional throttles you've ever used.
I am a bit rusty on A-320 system details but that is pretty darn close to how it happened and why.
They were intentionally flying just below 100 feet right at stall speed with the RA inhibiting A.FLOOR trigger. The FO was to maintain speed manually, while the CA flew the plane. They planned on doing a hard pull back with TOGA application at the end.
They drifted down to about 40 feet, realized they were too low with the trees approaching and pulled back while they went to TOGA.
Since they were already at alpha limit due to the poor control of airspeed/hot dogging, they got the airbus equivalent of a stick pusher.
About the time the manually selected TOGA power kicked in, they were entering the trees.
06-29-2014, 10:02 PM
#952
Da Hudge
Joined APC: Oct 2006
Position: Poodle Whisperer
Posts: 17,473
Originally Posted by badflaps
When I first checked out on the 767 I loved A/T till the day I flared and put both hands on the yoke and the throttles went right back up to bug. Only happened once.....
Always 1 hand on the yoke/stick, one hand on the TLs! (and the 767 is twitchy... no need for 2 hands on that yoke!)
06-30-2014, 07:44 AM
#953
Gets Weekends Off
Joined APC: Jan 2009
Position: B744 F/O
Posts: 141
Had some issues when I went from 744 to 757 a few years ago. The AT disconnect switch on the 744 is the GA switch on the 757. First day in the sim and ready to click the AT off, hey why is this thing going around! Instructor laughed and said happens all the time. They beat it out of me by the type ride.
Tr
Tr
06-30-2014, 08:12 AM
#954
Banned
Joined APC: Nov 2008
Position: A330
Posts: 1,043
Originally Posted by badflaps
When I first checked out on the 767 I loved A/T till the day I flared and put both hands on the yoke and the throttles went right back up to bug. Only happened once.....
I always turned off A/T by final approach fix on 767.
The Asiana guys crashed because of some embedded cultural habits that don't belong in the cockpit coupled with shi**y training.
06-30-2014, 09:04 AM
#955
Gets Weekends Off
Joined APC: Apr 2011
Position: retired 767(dl)
Posts: 5,724
Originally Posted by 80ktsClamp
Ha! I can completely see that happening. Always 1 hand on the yoke/stick, one hand on the TLs! (and the 767 is twitchy... no need for 2 hands on that yoke!)
Always 1 hand on the yoke/stick, one hand on the TLs! (and the 767 is twitchy... no need for 2 hands on that yoke!)
06-30-2014, 02:07 PM
#957
Gets Weekends Off
Joined APC: Apr 2009
Position: Hiding under the counter
Posts: 276
Curious, is it fairly normal to be selecting descent rates like that in good visual conditions?
I can understand initially setting something in, but then haphazardly changing it on final? Perhaps I'm a bit naive, but I would have assumed one would fly the yoke at that point if the plane starts to get significantly off of GS, not mess with a descent rate. It seems he could have caught the whole problem a long time before having to cut to idle, and the the auto throttle misunderstanding that followed.
EDIT: after thinking about that point another moment, I guess the auto throttle would be coupled to what you selected as a descent rate. So perhaps if he didn't want to hand fly, that is the only way to keep the throttles where you want them?
I can understand initially setting something in, but then haphazardly changing it on final? Perhaps I'm a bit naive, but I would have assumed one would fly the yoke at that point if the plane starts to get significantly off of GS, not mess with a descent rate. It seems he could have caught the whole problem a long time before having to cut to idle, and the the auto throttle misunderstanding that followed.
EDIT: after thinking about that point another moment, I guess the auto throttle would be coupled to what you selected as a descent rate. So perhaps if he didn't want to hand fly, that is the only way to keep the throttles where you want them?
06-30-2014, 04:05 PM
#958
Gets Weekends Off
Joined APC: Jul 2008
Posts: 854
Originally Posted by Globerunner513
EDIT: after thinking about that point another moment, I guess the auto throttle would be coupled to what you selected as a descent rate. So perhaps if he didn't want to hand fly, that is the only way to keep the throttles where you want them?
The problem started when he made the mistake of selecting the flight level change (FLCH) vertical mode. The altitude alerter was already set to 3,000', their missed approach altitude, so the airplane began to CLIMB back to 3,000' by increasing thrust to climb and pitching up to maintain airspeed.
At this point he disconnected the autopilot, to try to fix his mistake and stop the climb, and pulled the thrust levers back to idle. Pulling the thrust levers back to IDLE changed the A/T mode from SPEED to HOLD. The A/T was still active but it was no longer maintaining speed--end it didn't. This is why the A/T didn't increase power when they got too slow.
The F/D (the A/P was now off) would still be displaying pitch commands to maintain the speed, and may have contributed to them ended up so low, but he soon called for the F/D to be switched off. As far as I recall, the DFDR transcript did not indicate that the vertical mode ever changed from FLCH.
07-01-2014, 02:58 AM
#960
Gets Weekends Off
Joined APC: Jul 2008
Posts: 854
Originally Posted by DCA A321 FO
Is the 777 capable of a VNAV approach?
Does FLCH call for an idle descent on 777?
If he had descended in FLCH the power would have gone to idle but would have increased again once they started to slow. Pitch would have pitched down for the descent then back up again when capturing the selected altitude.
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