To keep the signal-to-noise ratio higher in these post-accident posts, it might be a good idea to establish a basic commenting criteria for speculating on causes of aircraft accidents.
First a word about aircraft strength. Transport category aircraft are certified to a standard known as FAR Part 25 which dictates among other things ultimate load limits which the aircraft must survive. One of these limits is the 55 feet/sec gust (essentially a huge thunder storm), while traveling at Vmo. That's ALOT of stress on the wingspar, and the fuselage. The fact that an aircraft can be built light enough to get airborne, withstand high speed flight loads, but still maintain a shape resembling an aircraft after running across the ground and falling into a ravine without wheels at 145 kts is a testament to the relative strength of the airframe. Try that with any car short of a Hummer.
As for the cause of the accident, at this point we know absolutely nothing about what caused the departure from controlled flight. If you feel you MUST speculate, please at least consult a pilot, or have detailed operation of flight operations, or at the very least access to someone who does.
Though I usually avoid commenting before the experts do, as I hold a commercial multi-engine rating and have some turbine time, I can at least present some possible options:
* tire blow out: If anyone ever has had a blowout of a front tire in their car at highway speeds, you know exactly what kind of challenge you face with directional control if one of them goes. V1 (go / no go speed) in a fully loaded 737-500 would be around 145kts. Complete loss of left tire would cause a severe asymmetric rolling moment, and if the crew hesitated on the rudder (or maybe ran out of rudder given wind gust and gear drag), they simply may not have had enough time to catch it. From the track marks though, it looks like both gear were intact at runway departure
* Asymmetric (split) flap / incorrect flap condition - there is some speculation the aircraft went airborne for a moment or so. If the flaps had been mis-set, or worse, had an asymmetric setting (mechanical failure), this may have caused the aircraft to momentarily roll or even yaw left, and again, depending on the reaction time of the crew, the yaw moment may have been too quick to catch.
* Uncommanded left-rudder movement - Over there years, there have been numerous incidents involving uncommanded rudder movement in 737s, including a speculated one in Steamboat springs with United airlines several years back. Uncommanded flight control movements, needless to say are as dangerous as in-flight fires, as they can render the aircraft uncontrollable in a matter of seconds, and lead to catastrophic results, especially near the ground. An uncommanded left rudder movement could easily have given enough steering yaw moment to have the aircraft depart controlled flight, and off into the grass.
There are other failure modes possible, but I think you guys get the idea. Again, speculation about accident is understandable, but please try to make it based on rational possibilities, and not simply fantastical guessing.
On the bright side, all the passengers are probably getting healthy holiday "bonuses" from the airline to prevent lawsuits. Emotional trauma aside, it might have been a good thing for the people who were not injured.
I read that some guy sent off a message to his Twitter blog a few minutes after it all happened, like saying 'heck, I've just been in a friggin plane crash...' or so....
And he took Continental's offer of a replacement ticket two days later. That guy was one tough (or mad) nut, for sure.
@yogibimbi: I had a deer run into my car. The way I see it, the chances of TWO deer running into my car in my lifetime are astronomical. So the chances of this guy being in two plane crashes is higher than mine, so he's fine.
Some of the reports reported the plane stopped a short distance from one of the airports' fire stations. Pure speculation on my part, but if the structures in the photos is indeed one of those fire stations, the pilot may have had a warning in the cockpit and driven the plane in that direction.
@taylors_dad: You don't drive TOWARDS a building in an out of control aircraft. You try to minimize damage to the craft and what/who is on the ground. Blowing up the place where everyone is waiting to rescue you and put the fire out isn't a good idea.
12/24/08
12/23/08
First a word about aircraft strength. Transport category aircraft are certified to a standard known as FAR Part 25 which dictates among other things ultimate load limits which the aircraft must survive. One of these limits is the 55 feet/sec gust (essentially a huge thunder storm), while traveling at Vmo. That's ALOT of stress on the wingspar, and the fuselage. The fact that an aircraft can be built light enough to get airborne, withstand high speed flight loads, but still maintain a shape resembling an aircraft after running across the ground and falling into a ravine without wheels at 145 kts is a testament to the relative strength of the airframe. Try that with any car short of a Hummer.
As for the cause of the accident, at this point we know absolutely nothing about what caused the departure from controlled flight. If you feel you MUST speculate, please at least consult a pilot, or have detailed operation of flight operations, or at the very least access to someone who does.
Though I usually avoid commenting before the experts do, as I hold a commercial multi-engine rating and have some turbine time, I can at least present some possible options:
* tire blow out: If anyone ever has had a blowout of a front tire in their car at highway speeds, you know exactly what kind of challenge you face with directional control if one of them goes. V1 (go / no go speed) in a fully loaded 737-500 would be around 145kts. Complete loss of left tire would cause a severe asymmetric rolling moment, and if the crew hesitated on the rudder (or maybe ran out of rudder given wind gust and gear drag), they simply may not have had enough time to catch it. From the track marks though, it looks like both gear were intact at runway departure
* Asymmetric (split) flap / incorrect flap condition - there is some speculation the aircraft went airborne for a moment or so. If the flaps had been mis-set, or worse, had an asymmetric setting (mechanical failure), this may have caused the aircraft to momentarily roll or even yaw left, and again, depending on the reaction time of the crew, the yaw moment may have been too quick to catch.
* Uncommanded left-rudder movement - Over there years, there have been numerous incidents involving uncommanded rudder movement in 737s, including a speculated one in Steamboat springs with United airlines several years back. Uncommanded flight control movements, needless to say are as dangerous as in-flight fires, as they can render the aircraft uncontrollable in a matter of seconds, and lead to catastrophic results, especially near the ground. An uncommanded left rudder movement could easily have given enough steering yaw moment to have the aircraft depart controlled flight, and off into the grass.
There are other failure modes possible, but I think you guys get the idea. Again, speculation about accident is understandable, but please try to make it based on rational possibilities, and not simply fantastical guessing.
Thanks
-avi
12/24/08
12/23/08
12/23/08
12/23/08
And he took Continental's offer of a replacement ticket two days later. That guy was one tough (or mad) nut, for sure.
12/23/08
12/23/08
12/23/08