Bagram airfield crash question

Factual Questions
1

A 747 cargo plane crashed at Bagram airfield last week. The crash was captured by the dasboard camera of a ground vehicle.

The video is here. I’m two-clicking it because it shows seven people dying, and some people might be disturbed by that thought.

- YouTube

If you turn your computer’s volume way, way up (AFTER the first second; turn it down again before the final second), you can hear something that sounds like engine thrust at around the 8-second mark. The plane is probably a good 1/4-mile from the camera, so assume any sounds coming from the airplane are being heard one second after they are created. It’s been puzzling to me, because until recently I assumed the plane would already have been at max thrust and so would not have any more thrust to add.

a 747-400 cargo plane has a capacity of 124 tons, and the 5 MRAP vehicles this plane was carrying reportedly weigh about 15 tons each, so 75 tons total. They were only going to be flying about 1000 miles to Dubai, so presumably they would have had a fairly light load of fuel.

Questions:
When a plane is lightly loaded with fuel and cargo, do they still climb at something close to maximum thrust?

If they don’t normally do so, would they still do so at Bagram, in order to minimize vulnerability to attack from the ground by small arms fire?

What exactly are we hearing in the video that starts at ~8 seconds? Is that the sound of the pilots commanding absolute lord-help-us-now max power, or is it some sort of aerodynamic noise due to the slipstream hitting the wings and fuselage at really weird angles of attack?

2

I’m not sure about flying out of Bagram, but civilian airliners do derated thrust takeoffs as a matter of course.

3

If anything, I would have expected to hear them reduce power if they had any time to assimilate and contemplate what was happening. AIUI, a typical departure from Bagram is rather steep, so there’s probably not much range between a normal takeoff from there and “Our climb rate is too high, we’re about to stall! Cut the power, retract the flaps, try to get the nose down!”

Hopefully, both flight recorders will have usable information. Until they’re recovered and analyzed, all we can do is guess at what happened.

4

I know “get the nose down” is appropriate for an imminent stall, the point being to

A)reduce AoA and
B)increase airspeed (or at least reduce deceleration).

Retracting flaps would cut drag, but it would also increase the stall speed; if a stall is already imminent, I’d expect this to make it happen.

If a stall is imminent, how does reducing thrust help?

5

I don’t think it’s physically possible to recover a stall at that altitude with such a large aircraft.

6

It sort of looks like the plane is trying to climb out from behind the power band. It’s as if some of the cargo came lose and shifted to the rear of the aircraft making pitch control difficult if even possible.

7

I had heard speculation that the load might have shifted suddenly. A sudden change in weight and balance can be a handling nightmare. Insufficient pilot training via simulators could be part of the cause of this event.

8

I read the plane was carrying 4 MRAPs, for a total of something like 75 tons of cargo. I suspect that even one of those breaking loose and not being where it’s supposed to be would seriously upset the center of mass and gravity of the plane and make it do all kinds of squirrely stuff.

9

Depends on your definition of “stall”. If it’s a very brief excursion to an AoA just past maximum, then you should be able to push the nose back down and get back to flying without losing a ton of altitude. That’s not what happened to these guys; they were in a deep stall at low airspeed where there was not enough pitch authority to fight the tail-heaviness (due to cargo shift) and get the nose back down.

5 MRAPS (but still 75 tons). I assume it was a steep climbout (to avoid small arms fire from the countryside), and that could have contributed to one of the MRAPS breaking loose. I don’t know what kind of safety factor they employ when tying these vehicles down, but I’d expect that one of them rolling back into another one might be enough to rip that one loose too, and start a chain reaction that could move two or more MRAPS to the back of the plane.

10

In a passenger aircraft, say a 747-400, can the weight of human passengers create a similar problem? Suppose, someone turned a tiger loose in the forward cabin and the passengers suddenly rushed to the rearmost section of the airplane. Could they cause a similar problem, or are humans simply not heavy enough to upset such a large airplane?

11

Well a 747-400 can carry about 400 people, depending, and they are going to weight about 30 tonnes, give or take.

We don’t know how many of the MRAP’s busted loose and shifted to cause this crash but 30 tonnes is a fair percentage of 75 tons, so maybe shifting people could do it.

Of course MRAP’s are probably way more dense than people are going to be: what with lack of seating and aisle room you just couldn’t get all 400 people into the very rear of a 747, they would of necessity be spread from aft forward to a substantial degree.

12

Ok just a query here.
Does anyone know why the video is dated February 1?
y outube.com/watch?v=lksDISvCmNI

13

As mentioned earlier, the current speculation is focusing on the load shifting. If that were the case, they likely were trying to get the nose down.

The elevator on the tail, which controls that pitch, is limited in how much nose down force it can generate. At slower airspeeds such as right after takeoff, there is not much air flowing over the elevator, so the amount of nose down force available is much lower than it would be in high speed cruise.

Very crudely put, an airplane and its load balances like a seesaw in normal circumstances. If you were to slide all the load to one end, it would require a much greater force to counteract that load on the other end. The elevator is what would provide that counteracting force. But, with a massive shift in weight, and little airflow over the tail, you can push the yoke all the way forward (nose down) and the elevator isn’t going to do a damn thing for you.

Incidentally, (based on the jets I’ve flown), the recovery procedure for a departure stall would be something like:

Max Power
Spoilers in
Reduce Pitch (not to the point where the nose is pointed down at the ground- remember, the ground is theoretically very close at this point)
Wait for the airspeed to recover to certain point, and for the airplane to gain altitude- known as “Positive Rate”
Only when the airplane is flying again do you retract the flaps/gear

In a simulator situation (thank god the only kind of departure stall in a swept wing aircraft that I’ve seen), the airplane has enough power to “fly out” of the stall. I don’t know if it would be recoverable with only 1000 feet of altitude though. If you look closely, they never got the gear up, which means they were likely in a lot of trouble well before they reached 1000 feet.

Thanks for the broken link, by the way. The day this happened, someone sent me the link with no explanation. Watching it was like a punch to the gut. It does look like they were fighting it. It’s sickening imagining fighting something like that with no hope for recovery.

14

First of all, the maximum thrust available for take-off may be less than the actual maximum thrust if you just firewall the thrust levers. If they were using maximum take-off thrust, they may still have had thrust in reserve that would take the engines beyond their design limits but would still be usable in an emergency.

It depends on the plane. Taking off with reduced thrust significantly reduces wear on jet engines so it is normal to use less than max thrust if you have the performance available to do it. Pilots in our company are required to do one max thrust take-off once a week to check the engines are producing their rated thrust, other than that pretty much every take-off is reduced thrust.

The way this works for us is we check the take off performance for an outside air temperature that is higher than what it really is, and if that performance is ok, we use the max thrust that would be available on a day at that temperature. As temperature goes up, available thrust reduces, so instead of using around 94% N1 (fan speed) we are using 88%.

I’m pretty sure they’d use max thrust for the reasons you state. I’ve heard, but don’t have any first hand knowledge, that they use a standard noise abatement climb procedure to get a good initial angle of climb. It would be logical that they’d use max thrust though because they’re not actually trying to minimise noise.

I think it might just be changes in sound as the aircraft turns and gets closer.

The thrust vector on most aircraft is below the drag vector, this results in a thrust/pitch couple that causes the nose to pitch up when thrust is increased and to pitch down when thrust is decreased. As their very first priority is to get the aircraft flying again, it is possible they might have tried reducing thrust. I’m not saying they would have done that, just that it is something they may have tried if all other options were exhausted.

Simulator training won’t help much with a load shift. A load shift can make the aeroplane literally unflyable and it is of little value to train for an event that is extremely unlikely to happen and if it does happen there is very little you can do about it.

15

Probably the same reason my microwave has the wrong time on it. If a bit of technology doesn’t automatically set the correct time and date it is pretty common for the user to not bother setting it correctly.

16

The pilot reported a cargo shift. If one of the vehicles came loose it’s pretty much a fatal event at 1300 feet AGL. IF at the exact moment the load shifted they banked hard over there is a miniscule chance they could get the load to reshift forward. But this was 30,000 lbs of load shifting.

MRAP’s are large vehicles so they would be have to be center loaded like this so the pallet it’s sitting on is not tucked in under the side rails on each side but under the lip of individual floor locks. The straps used are probably 5000 lb straps. So if you use half the capacity of the strap you would be using up to 12 straps for each direction of travel. It takes a lot of straps (and time) to secure 5 of these vehicles.

If one of them breaks loose the change in weight and balance would exceed the lift of the plane’s elevator trim. There is no way keep the nose level so no matter how much power is used the plane will stall with full power on.

Realistically, if one of these broke loose it could not be shifted back without destroying the plane’s structural integrity. Most of the structural strength is in the floor of the plane. That’s it’s backbone.

17

Is there a reliable source for the pilot reporting a cargo shift?

18

haven’t seen a preliminary NTSB report yet. This came from someone listening in on the frequency. No idea of the validity.

19

Looking at the link I just posted it shows the crash literally at the end of the runway.

20

My son just finished training for a new type-rating (BE-300). The trainers in the sim twice threw in a Kobyashi Maru situation (unrecoverable wind-shear after takeoff) as a training demo. They said this was part of their normal training syllabus.