Post by LOU on Jul 8th, 2013 at 7:14pm
I have to agree with Bruce of Lost in Isaan:
The 777 is truly a sturdy built aircraft. The amount of structure that remained at zero motion was remarkable.
The following is speculation
Here is a printout from a site that records flights from radar information.
http://flightaware.com/live/flight/AAR214/history/20130706/0730Z/RKSI/KSFO/tracklog
Interesting data here. Less than 2 min to landing, he was at 169 kts/194 mph passing 1400', vertical speed 1380 fpm down. Descent rate remains at 1300 fpm or more until 600' above the ground with decreasing airspeed. Airspeed continues to decay to below normal as descent rate decreases to a more normal value. Looks like the nose is coming up but without power increase. Then at 100' above the ground (water) airspeed is down to 109kts, looks like a big pitch up at low airspeed. Likely they were in a stall condition prior to touchdown. Fits a classic high unstabilized visual descent with an pitch overcorrection near the ground with little to no power increase leading to a stall. Just my opinion from the raw data.
I flew a few approaches in the CS 777 to see what it would look like from the cockpit and the ground. I set a landing weight around 400,000# which gave me a Vref of 129 kts. After flying several approaches and doing screen captures of the approach I came up with these two shots.
Here is the plane in landing configuration. I have less than the necessary thrust set to make the speed bleed off to near stall.
The speed in this picture is 108 KTS and a vertical speed of -420 FPM @ 100 feet above the runway, with 10 degrees nose up.
I continued to raise the nose to touchdown where I obtained a pitch angle of almost 15 degrees and in stall buffet the last 50 feet above the TDZE.
Here is a snap of the plane just prior to touchdown.
In this case, I was able to land on the runway in stall buffet and just scrape the aft part of the plane. If I had been just a little lower on this approach the gear and the aft of the plane would have hit short of the runway. It looks like, from the cell phone video and passenger reports, that the plane actually skimmed the water prior to hitting the rock wall.
Now, I have never flown the 777, but the other Boeing planes like the 747 and 767 all have pretty much the same auto-thrust system. The throttles are driven by a slip clutch when A/T is engaged. You can override the throttle movement while the A/T system is still engaged. This is something I would do many times to make small corrections to the speed. Since the plane was high and fast, I wonder if the pilot disengaged the A/T during the descent in order to get the plane down into the slot and then "forgot" to re-engage, or thought they were engaged. He could have just kept his hand on the throttles and held them at idle, but if he moved his hand off the throttles to maybe do something else the throttles would have increased if the speed was below what was dialed in on the glare shield speed window. In any event, I can only guess that the A/T were not on during the last portion of the flight and that resulted in a speed bleed as the nose was slowly raised during the last part of the approach.
BTW, during several of my simulated approaches, I kept the throttles back during the last portion of the approach in order to force the stall around 100 feet above the ground. Each time I got the speed down to around 106 KTS, buffet would occur. If I applied full thrust at that point almost every time the plane would make a successful go-around.
Lou
Uploaded with ImageShack.us
The 777 is truly a sturdy built aircraft. The amount of structure that remained at zero motion was remarkable.
The following is speculation
Here is a printout from a site that records flights from radar information.
http://flightaware.com/live/flight/AAR214/history/20130706/0730Z/RKSI/KSFO/tracklog
Interesting data here. Less than 2 min to landing, he was at 169 kts/194 mph passing 1400', vertical speed 1380 fpm down. Descent rate remains at 1300 fpm or more until 600' above the ground with decreasing airspeed. Airspeed continues to decay to below normal as descent rate decreases to a more normal value. Looks like the nose is coming up but without power increase. Then at 100' above the ground (water) airspeed is down to 109kts, looks like a big pitch up at low airspeed. Likely they were in a stall condition prior to touchdown. Fits a classic high unstabilized visual descent with an pitch overcorrection near the ground with little to no power increase leading to a stall. Just my opinion from the raw data.
I flew a few approaches in the CS 777 to see what it would look like from the cockpit and the ground. I set a landing weight around 400,000# which gave me a Vref of 129 kts. After flying several approaches and doing screen captures of the approach I came up with these two shots.
Here is the plane in landing configuration. I have less than the necessary thrust set to make the speed bleed off to near stall.
The speed in this picture is 108 KTS and a vertical speed of -420 FPM @ 100 feet above the runway, with 10 degrees nose up.
I continued to raise the nose to touchdown where I obtained a pitch angle of almost 15 degrees and in stall buffet the last 50 feet above the TDZE.
Here is a snap of the plane just prior to touchdown.
In this case, I was able to land on the runway in stall buffet and just scrape the aft part of the plane. If I had been just a little lower on this approach the gear and the aft of the plane would have hit short of the runway. It looks like, from the cell phone video and passenger reports, that the plane actually skimmed the water prior to hitting the rock wall.
Now, I have never flown the 777, but the other Boeing planes like the 747 and 767 all have pretty much the same auto-thrust system. The throttles are driven by a slip clutch when A/T is engaged. You can override the throttle movement while the A/T system is still engaged. This is something I would do many times to make small corrections to the speed. Since the plane was high and fast, I wonder if the pilot disengaged the A/T during the descent in order to get the plane down into the slot and then "forgot" to re-engage, or thought they were engaged. He could have just kept his hand on the throttles and held them at idle, but if he moved his hand off the throttles to maybe do something else the throttles would have increased if the speed was below what was dialed in on the glare shield speed window. In any event, I can only guess that the A/T were not on during the last portion of the flight and that resulted in a speed bleed as the nose was slowly raised during the last part of the approach.
BTW, during several of my simulated approaches, I kept the throttles back during the last portion of the approach in order to force the stall around 100 feet above the ground. Each time I got the speed down to around 106 KTS, buffet would occur. If I applied full thrust at that point almost every time the plane would make a successful go-around.
Lou
Uploaded with ImageShack.us