Turbine Failure

[tom slick]

With Shannow's photo of a turbine failure in the Industrial section i thought I'd share a couple of pics of a C-130 turbine failure.

This plane landed at Al Ueid AB while I was there in 2003. I pulled the engine off the wing after inspecting it for a write-up of high vibration and shut-down in flight. the crew "saw sparks".

It liberated the rear bearing and rear oil pump somewhere over Saudi Arabia.
This was caused by a rear oil pump failure, which caused the rear bearing to fail, which caused vibration, which caused the struts to fail and the oil pump/bearing assy to fall off, which caused the turbine to fail. it did send parts through the turbine case.

The flight engineer attempted to explain to me how the turbine failed causing the oil pump/rear bearing to liberate, those guys know everything

some specs are:
Allison T-56 engine
13,000 rpm constant
about 24" diameter turbine
about 3500 horsepower
about 1600 lb-ft torque

 

[Shannow]

tom slick,
thanks for the pics.

In my world it is very uncommon for the fir trees (root attachments) to tear off the disk.

"High vibration"...the words give me shivers sometimes.

 

[FrozenPilot]

Only 1600lb-ft? I guess thats before the prop reduction gearbox. The 675shp PT6 on the C208B is rated to 1865lb-ft at 1900RPM on the prop.
Nice pics BTW.

 

[tom slick]

it's actually 19,800 in-lb on the guage measured at the torque shaft between the engine and RGB. doing some quick math...1600 lb-ft X 13:1 reduction = 20,800 lb-ft.

The J model RR powerplant did away with torque measurements altogether and calculates horsepower output. the AE2100 engine is capable of 6,000hp but the C-130J airframe limits it to 4,600hp. that margin makes the engine never have low power due to wear/loss of efficiency like the old T-56 did.

 

[CBDFrontier06]

One reason I don't like sitting at the back of an S80, 727 or CRJ. Doesn't happen often, but when it does.....

 

[tom slick]

What failed on that engine?

it is very difficult for an engine to throw parts out of the cases with enough velocity to cause damage to the passenger compartment.

I used to stand next to the engines while they were on the test stand. it's fun to check for leaks with a 10' prop spinning next to you.

 

[CBDFrontier06]

I can't find any facts concerning the picture I posted...perhaps a turbine blade?
Something similar happened with a Delta MD88 in Pensacola in 1996. I used to have a picture of the Pensacola plane but can't find it now. It put a sizeable hole in the fuselage, but thankfully the takeoff roll had just begun.

"Uncontained engine debris from the front compressor front hub (fan hub) penetrated the left aft fuselage. Two passengers were killed and two others were seriously injured." --NTSB.ORG

I recall reading elsewhere that a piece of the blade was located embedded in the first aid kit mounted to the wall inside the plane. Scary stuff.

 

[tom slick]

this the the NTSB write-up for the pensacola bird.
http://www.airdisaster.com/reports/ntsb/AAR98-01.pdf
the fan hub was not inspected correctly and the had a catastrophic failure. that stems from poor maintenance practices and complacency.

 

[FowVay]

I'm a NDT inspector at Delta and I can tell you that the Pensacola incident shook that place up in a hurry. I would like to say that the inspection that took place on the fan disk was done exaclty as prescribed in Pratt's SPOP and cross referenced to Delta's own process standard.

I'm not at liberty to discuss exactly what took place during the investigation but I will tell you that it changed the inspection techniques for all of these disks.

Rolls Royce always required that their critical rotating parts got oven dried before FPI inspection. Pratt never required that. many cleaning techniques such as 'flash drying' of the parts were done incorrectly and even the inspection technique itself was inadequate to find the crack that led to the catastrophic failure of the -219 in Pensacola. Volvo had actually made nine faulty disks for these engines. Our disk had been inspected several times and the crack was never detected.

Now all bolt holes and cooling holes get FPI inspected and Eddy Current inspected. There's currently a similar situation with the CF6-80A2 engine that we fly on our B767. Worldwide airworthiness directives to FPI, acid etch, FPI, acid etch, then eddy current inspect the blade slot bottoms to try to detect these incredibly tiny stress fractures that are present in the first and possibly second stage HPT.

That 777 in London is going to be a interesting finding. Complete complacency of the autothrust mechanism when in autopilot and manual mode... was it computer or fuel problem? I hope we learn soon before the next one decides to go limp on final approach.

 

[Shannow]

FowVay,
thanks for the post.

 

[blackcherry06]

Stumbled across a picture of what I believe to be the Pensacola plane. Ouch

 

[outrun]

Even though these uncontained failures are rare ... would a belt of Kevlar or some sort of ballistic material be suitable to shield the aircraft vitals systems ... from flying metal?

 

[tom slick]

There is some containment measures in newer engines. the problem is the amount of mass that spins at those velocities creates tons (literally) of force.

 

[Shannow]

tom's correct.

The last stage of the (steam) turbines that I have at work have a blade 33.5" long, hanging off around a 4' disk, spinning at 3,000RPM.

The pins holding them to the disk experience a 200 tonne load at operating speed.

The "shroud" around them is 1-1/2" thick steel, and if a blade tries to escape, we've seen 1" dents from the inside out.

 

[bar1]

Originally Posted By: FowVay
That 777 in London is going to be a interesting finding. Complete complacency of the autothrust mechanism when in autopilot and manual mode... was it computer or fuel problem? I hope we learn soon before the next one decides to go limp on final approach.

Did they find the fault with the 777 at Heathrow, London?

 

[FrozenPilot]

Last I heard they were still investigating. They've found no mechanical failure but found abnormal cavitation in the high-pressure fuel pumps which could signal a restriction or just excessive aeration. Either way they could develop full flow. The engines just weren't responding to commands and were producing something less than what the autothrottles and pilots were commanding.

American had one of their 777-200ER have a nearly identical problem a month later, but only on the left engine. Both aircraft had Rolls-Royce Trent 800 engines.

 

[Propflux01]

Originally Posted By: tom slick
it's actually 19,800 in-lb on the guage measured at the torque shaft between the engine and RGB. doing some quick math...1600 lb-ft X 13:1 reduction = 20,800 lb-ft.

Actually 19600 max in-lb for the guage measurement, and 13.54-1 reduction. Those pics of that liberated turbine is actually not that uncommon, I have seen a few that all that remained was the 4th stage, even the support assy was gone! We had one of our planes blew one out over greenland, MS and took out the wing causing a fatal incident. They can explode rather violently at times. lets just hope that one pictured in above posts landed on some al-qiada operatives' head!