UPS MD-11 crash

[Maxmars]

The fore and aft fracture surfaces failed, most likely the aft first, which allowed the engine to rotate up, from the thrust pushing it.

Hindsight being the favorite tool of arm-chair quarterbacks...

Can the materials used in those critical control points be a "culprit" in this scenario?
Or are these vehicle so heavily-used that they are undergoing long-term increased stress?
More wear, more tear.

Look at me... like I know anything about this stuff...

[Zaphod58]

Hindsight being the favorite tool of arm-chair quarterbacks...

Can the materials used in those critical control points be a "culprit" in this scenario?
Or are these vehicle so heavily-used that they are undergoing long-term increased stress?
More wear, more tear.

Look at me... like I know anything about this stuff...

Some of the fractures found were consistent with over stress of the mount, most likely caused by high power settings being left for long periods of time. Other fractures were consistent with wear and age. So it's a combination of heavy use, and stress. The accident aircraft had just short of 100,000 hours on the airframe, and just over 21,000 cycles.

[Zaphod58]

According to the NTSB report, UPS performed a general visual inspection, and detailed visual inspection of the aft mount October 28, 2021. The inspection is required under UPS maintenance requirements every 72 months.

[RickyD]

Some of the fractures found were consistent with over stress of the mount, most likely caused by high power settings being left for long periods of time. Other fractures were consistent with wear and age. So it's a combination of heavy use, and stress. The accident aircraft had just short of 100,000 hours on the airframe, and just over 21,000 cycles.

Do you think this will lead to a different standard for maintenance cycles? Like instead of 72 months maybe 36? Or possible a system to flag a plane who's pilot had the power settings too high too long?

[Zaphod58]

Do you think this will lead to a different standard for maintenance cycles? Like instead of 72 months maybe 36? Or possible a system to flag a plane who's pilot had the power settings too high too long?

They'll probably keep the visual inspection at 72 months, but decrease the cycle inspection by several thousand cycles.

[EXETER]

Don’t believe people that are making wild claims based on American 191. That can’t happen again. After AA191 and UA232 significant changes were made. In AA191 that’s exactly what happened. As a result physical locks were placed in the slats that holds them in place regardless of hydraulic status, unless the slat handle is moved in the cockpit.

 After UA232, where the fan blade broke all three hydraulic lines and caused a complete loss of hydraulic fluid, fuses were placed at various points in the hydraulic system. When these fuses are activated they physically block the hydraulic line and prevent the complete loss of fluid from a broken hydraulic line. 

And that’s the long way of saying, no the slats almost certainly didn’t roll back due to loss of hydraulic fluid. The aircraft rolled left because the right engine was producing full power, and was the only engine producing full power, so the right wing was producing more lift than the left wing and there was no way to correct that.

I'll take your word for it that the FAA fixed the hydraulic line failure mode with mechanical locks on the leading edge slats.  Thanks for pointing that out.

However........

I don't think the accident facts are consistent with a simple asymmetric thrust explanation.  All multi-engine transport aircraft are designed so that they can withstand an engine loss of thrust in worst case conditions and still execute a controllable takeoff and climb.  Worst case, of course is at maximum takeoff weight right at the time of rotation--which basically describes the conditions here.  If the only thing that happened after the left engine departed the wing was loss of thrust on that side, they should have been able to control the roll attitude of the aircraft.  

If they had also lost thrust on the center engine, that would have reduced the total thrust available and they probably wouldn't have been able to climb.  But that wouldn't change the asymmetric thrust situation. In that case, they should have impacted the ground in a wings-level attitude.

The only thing that could have caused a large roll excursion to the left in the 30 feet of altitude they attained is a large loss of aerodynamic lift on the left wing. 

The NTSB released some photos today which I think sheds more light on the situation. They show that the left engine and the pylon as a unit departed the wing, with the engine/pylon unit apparently pitching up and pivoting around the front attach pin, before breaking off and flying up above the wing and fuselage, in flames.  When it departed, it apparently caused enough structural damage to create a large fireball on the upper surface of the wing that persisted until the aircraft crashed.  Most likely, the fireball was the result of one of the wing fuel tanks rupturing because of the structural damage.  

Any event that was energetic enough to cause structural damage to the wing would also be energetic enough to cause failure of slats or flaps regardless of mechanical locks.  In NTSB photo #1, the outer leading edge slat is clearly deployed.  In photo #6, it is not so obvious to me whether whether it is or isn't.  Also, the photos don't show anything about the flaps.  And for that matter, the wing camber of the upper surface of the wing could simply have been deformed enough by the engine/pylon departure that the lift coefficient deteriorated.

I'm still betting that sudden loss of lift on the left wing is going to figure in to the final report.

[Zaphod58]

I'll take your word for it that the FAA fixed the hydraulic line failure mode with mechanical locks on the leading edge slats.  Thanks for pointing that out.

However........

I don't think the accident facts are consistent with a simple asymmetric thrust explanation.  All multi-engine transport aircraft are designed so that they can withstand an engine loss of thrust in worst case conditions and still execute a controllable takeoff and climb.  Worst case, of course is at maximum takeoff weight right at the time of rotation--which basically describes the conditions here.  If the only thing that happened after the left engine departed the wing was loss of thrust on that side, they should have been able to control the roll attitude of the aircraft.  

If they had also lost thrust on the center engine, that would have reduced the total thrust available and they probably wouldn't have been able to climb.  But that wouldn't change the asymmetric thrust situation. In that case, they should have impacted the ground in a wings-level attitude.

The only thing that could have caused a large roll excursion to the left in the 30 feet of altitude they attained is a large loss of aerodynamic lift on the left wing. 

The NTSB released some photos today which I think sheds more light on the situation. They show that the left engine and the pylon as a unit departed the wing, with the engine/pylon unit apparently pitching up and pivoting around the front attach pin, before breaking off and flying up above the wing and fuselage, in flames.  When it departed, it apparently caused enough structural damage to create a large fireball on the upper surface of the wing that persisted until the aircraft crashed.  Most likely, the fireball was the result of one of the wing fuel tanks rupturing because of the structural damage.  

Any event that was energetic enough to cause structural damage to the wing would also be energetic enough to cause failure of slats or flaps regardless of mechanical locks.  In NTSB photo #1, the outer leading edge slat is clearly deployed.  In photo #6, it is not so obvious to me whether whether it is or isn't.  Also, the photos don't show anything about the flaps.  And for that matter, the wing camber of the upper surface of the wing could simply have been deformed enough by the engine/pylon departure that the lift coefficient deteriorated.

I'm still betting that sudden loss of lift on the left wing is going to figure in to the final report.

In an asymmetric thrust situation one wing is going to want to drop, because the other is producing more lift due to that engine producing thrust and the other not. With them at low speed, and heavy weight keeping control and keeping wings level was going to be difficult, with them impacting a building, and potentially getting more damage, it was going to get worse, especially with only one engine producing significant power.

 The left wing was going to stay on fire because the fuel was still flowing, and there was still some hydraulic fluid. It was only about 30 seconds from separation to impact. That’s not enough time for them to have recognized the loss of thrust, and attempted to shut the engine down, and cut off the fuel flow. The hydraulic fluid may have stopped due to the fuse in the line, but I’m not sure how long it takes for them to block the lines off.

[Sky727]

In an asymmetric thrust situation one wing is going to want to drop, because the other is producing more lift due to that engine producing thrust and the other not. With them at low speed, and heavy weight keeping control and keeping wings level was going to be difficult, with them impacting a building, and potentially getting more damage, it was going to get worse, especially with only one engine producing significant power.

 The left wing was going to stay on fire because the fuel was still flowing, and there was still some hydraulic fluid. It was only about 30 seconds from separation to impact. That’s not enough time for them to have recognized the loss of thrust, and attempted to shut the engine down, and cut off the fuel flow. The hydraulic fluid may have stopped due to the fuse in the line, but I’m not sure how long it takes for them to block the lines off.

AND with the loss of power from the left engine and with the right engine  supposedly still producing take off power the aircraft would have required a butt load of right rudder to maintain directional control.  They were screwed ....