By now you've seen the tragic footage of a Boeing 747 cargo plane crashing soon after takeoff from Bagram airport in Afghanistan.
What does this look like, from an aviation perspective? To get the caveats out of the way:
- I don't know first-hand that this is an authentic video, although it has been publicized widely without debunking that I have seen;
- It is certainly possible that there are causal factors that this video doesn't reveal, from sabotage to some external force somehow not shown on screen;
- And whatever else you can think of.
Still, if you ask what this looks like, the answer is: It looks like an aerodynamic stall.
As explained in, sigh, some previous crash posts here and here, an aerodynamic stall is nothing like a normal car-engine stall. The simplest way to envision it is to think of bicycling up a very steep hill in high gear. At some point, you won't be able to keep the bicycle's speed up -- and since a bike needs to be moving forward to stay upright, at that point it will fall down.
So too with an airplane. Its wings have to move through the air at a certain speed, conveniently known as "airspeed," to generate the lift that keeps the plane aloft. If they go too slowly, which often comes from climbing too steeply,* at some point they stop generating enough lift -- and then like a bike going too slowly up a too-steep hill, they will "fall over" the plane will come out of the sky.
That is what we seem to see in the video above, starting just a few seconds in. Every pilot has done "stall recovery" drills, in which you point the airplane too steeply upward, until eventually it stalls, noses over, and begins to fall. Then you recover in the prescribed way. But usually you do these drills a few thousand feet up into the sky -- to avoid exactly the fate shown in the video.
Why would an experienced flight crew get into this trouble -- if that is what occurred? Again, I don't know for sure, but one possibility would be "cargo shift." Suppose the cargo in a heavily laden plane was not securely strapped down, so that as the plane accelerated for takeoff, the cargo might shift toward the tail. That could make the plane too tail-heavy to fly. (To be more precise, it could shift the plane's center of gravity outside the acceptable flight envelope.) In general, a pilot increases a plane's airspeed -- and avoids the risk of a stall -- by pointing its nose down. The weight loaded into a plane is carefully calculated to be sure it is appropriately balanced between nose and tail; if the tail became too heavy, essentially making the plane a see-saw with too much weight on one side, the pilot would be helpless to avoid a stall and crash.
This is what this looks like. We'll learn more about what actually occurred.
__
* For the aviation crowd: yes, the technical term is here is that the angle of attack has become too acute.
Image may be NSFW.
Clik here to view.
Image may be NSFW.
Clik here to view.Image may be NSFW.
Clik here to view.Image may be NSFW.
Clik here to view.
What does this look like, from an aviation perspective? To get the caveats out of the way:
- I don't know first-hand that this is an authentic video, although it has been publicized widely without debunking that I have seen;
- It is certainly possible that there are causal factors that this video doesn't reveal, from sabotage to some external force somehow not shown on screen;
- And whatever else you can think of.
Still, if you ask what this looks like, the answer is: It looks like an aerodynamic stall.
As explained in, sigh, some previous crash posts here and here, an aerodynamic stall is nothing like a normal car-engine stall. The simplest way to envision it is to think of bicycling up a very steep hill in high gear. At some point, you won't be able to keep the bicycle's speed up -- and since a bike needs to be moving forward to stay upright, at that point it will fall down.
So too with an airplane. Its wings have to move through the air at a certain speed, conveniently known as "airspeed," to generate the lift that keeps the plane aloft. If they go too slowly, which often comes from climbing too steeply,* at some point they stop generating enough lift -- and then like a bike going too slowly up a too-steep hill, they will "fall over" the plane will come out of the sky.
That is what we seem to see in the video above, starting just a few seconds in. Every pilot has done "stall recovery" drills, in which you point the airplane too steeply upward, until eventually it stalls, noses over, and begins to fall. Then you recover in the prescribed way. But usually you do these drills a few thousand feet up into the sky -- to avoid exactly the fate shown in the video.
Why would an experienced flight crew get into this trouble -- if that is what occurred? Again, I don't know for sure, but one possibility would be "cargo shift." Suppose the cargo in a heavily laden plane was not securely strapped down, so that as the plane accelerated for takeoff, the cargo might shift toward the tail. That could make the plane too tail-heavy to fly. (To be more precise, it could shift the plane's center of gravity outside the acceptable flight envelope.) In general, a pilot increases a plane's airspeed -- and avoids the risk of a stall -- by pointing its nose down. The weight loaded into a plane is carefully calculated to be sure it is appropriately balanced between nose and tail; if the tail became too heavy, essentially making the plane a see-saw with too much weight on one side, the pilot would be helpless to avoid a stall and crash.
This is what this looks like. We'll learn more about what actually occurred.
__
* For the aviation crowd: yes, the technical term is here is that the angle of attack has become too acute.
Image may be NSFW.
Clik here to view.
| Image may be NSFW. Clik here to view.  Image may be NSFW.Clik here to view.  Image may be NSFW.Clik here to view.  Image may be NSFW.Clik here to view.  Image may be NSFW.Clik here to view.  |
Image may be NSFW.
Clik here to view.
Image may be NSFW.Clik here to view.
Image may be NSFW.Clik here to view.