Southwest engine failure

[FowVay]

The blade roots have a coating of copper-nickel-indium on the pressure faces. This sacrificial material prevents blade-to-disk contact. The visual inspection that occurs routinely at blade re-lube includes verifying the amount of Cu-Ni-In remaining. I can't quote off the top of my head but rarely is it allowed to have more than 10% of this coating missing.

By reapplying the molydag you are extending the service life of both the disk and the blade. Cu-Ni-In is applied at manufacture and overhaul and Molydag 254 is also applied during manufacture and overhaul. When new the Molydag is cured in an oven in order to ensure proper bonding. Routine maintenance affords only that the Molydag be brushed on and air dry at predetermined intervals such as every 100 cycles.

Another twist to this whole cycle is that once the blade slot dove tails on the disk become excessively worn they will broach the slots and then use shims to take up the slack.

The condition of the Southwest engine will likely never be disclosed. I do know that they turn an incredible amount of cycles on their engines. An AD will be issued very soon for further root inspection of these blades. Southwest just happens to have the highest level of exposure. No matter what the media spills about this you can be assured that this airline plays by the book and does their due diligence at keeping the fleet up to date.

 

[john_pifer]

Originally Posted By: FowVay
No matter what the media spills about this you can be assured that this airline plays by the book and does their due diligence at keeping the fleet up to date.


What makes you so sure?

 

[fdcg27]

Originally Posted By: john_pifer
Originally Posted By: FowVay
No matter what the media spills about this you can be assured that this airline plays by the book and does their due diligence at keeping the fleet up to date.


What makes you so sure?


Well, the airline has flown for decades with an enviable safety record.
That can't be just a matter of luck.

 

[nthach]

Originally Posted By: fdcg27
Originally Posted By: john_pifer
Originally Posted By: FowVay
No matter what the media spills about this you can be assured that this airline plays by the book and does their due diligence at keeping the fleet up to date.


What makes you so sure?


Well, the airline has flown for decades with an enviable safety record.
That can't be just a matter of luck.

And I also don't think WN has farmed out as much maintenance like other LCCs or even the legacy carriers do. Southwest does have a sizable MRO operation, and being common on one family of airplanes(but different submodels) does help keep the learning curve, parts inventory and risk of human error down.

There's been stories of subpar maintenance done overseas - granted Lufthansa, Singapore Airlines, EVA Air(EGAT), Korean Air and Cathay Pacific(HAECO) are also the biggest names in airline MRO. EVA Air's MRO operation is also a long-time Boeing partner - the 744BCF and LCF were converted over by EGAT.

 

[SEMI_287]

Incredibly sad incident and condolences to the womans family. That sure is an uncontained failure for sure. One blade from the disc destroyed the whole nacelle. MY worst nightmare for sure. Although the passengers not knowing how to use the oxygen masks is almost as frightening.


Originally Posted By: john_pifer
Originally Posted By: FowVay
No matter what the media spills about this you can be assured that this airline plays by the book and does their due diligence at keeping the fleet up to date.


What makes you so sure?


With very high utilization of equipment and a very good safety record I think we have something right.

 

[Astro14]

SWA has over 700 737 airplanes in Service. If there’s a problem with the jet, or the CFM-56, odds are that their fleet will be among the first to experience it. Two big failures in 18 months is enough of a data point to say that aging CFM-56 engines will need new maintenance procedures or inspection schedules.

But it is NOT enough of a data point to say that SWA is doing something wrong, they just have so many of these in Service that new problems will likely crop up with them first. Part of the NTSB investigation will be to go over Maintenance history and practice with a fine tooth comb.

In a year, we will know more.

 

[Astro14]

It is also fair to say, that since both of these uncontained engine failures were landed safely, without incident, despite additional damage to the airplane beyond the engine itself, that SWA has some excellent pilots.

 

[BusyLittleShop]

My best learned conjecture after studying the photos and what I know
of the CFM56 (KC135 USAF) say the fan casing failed first taking out
the fan blade... metal fatigue will be discovered in the fan casing
and not in the fan blade...

 

[Shannow]

Doubt it...

10 years as a turbine engineer, and I've never seen an externality take out a solitary blade, and leave it's peers untouched.

 

[Nyogtha]

I'm not a specific turbine engineer, but I have a couple of decades working experience with turbomachinery, especially "what went wrong and how do we address potential reoccurence" events. Some of the turbines I worked with had design speeds around 90,000 RPM, and I'd have to say my experience mirrors Shannow's.

 

[FowVay]

These engines don't spin nearly that fast. The low pressure (N1) speed is around 10,000 RPM and the high pressure (N2) speed is around 17,000 RPM. These things are small in size for an airplane engine, although you should see the cute little CF34

I work the CF6 and it's a virtual tortoise in comparison due to the size. It spins around 4800 RPM N1 and 7500 N2.**note: these RPM's are off the top of my head so don't nit pic if they're off by a few hundred.

The FAA issued an emergency AD (airworthiness directive) to have these stage 1 blades inspected in the next 20 days. The airports and maintenance hangars are hopping with NDT inspectors. The inspection is now an ultrasonic on-wing inspection. The blades already get an FPI and ECI during overhaul. Blades are NOT considered critical rotating parts although the disk that they attach to is. Blades are not life-limited either. The initial ultrasonic inspections are going to be on blades that have accumulated 30,000 cycles.

 

[SEMI_287]

I'm not a turbine engineer either but I can't see a piece of the nacelle taking out just one blade. N1 takeoff RPM is 5200 rpm on the -7B, certified max RPM is 5382 displayed 104%. 90,000 RPM holy moly!

 

[FowVay]

Semi_287, I went back and looked at the type certificate for the -7B and your times are much more accurate. It listed N1 at 5382 and N2 at 15183.

I think when people think of these super high RPM turbines they're thinking of tiny little car turbochargers. These CFM engines have a fan diameter of about 5 feet and getting that thing spinning around creates quite a high stress on the blade roots.

 

[SEMI_287]

I'm not sure we have the required metallurgy to get a CFM up to 90k RPM.

 

[FowVay]

I don't know,,, if the pilot misses a shift or accidentally goes from 5th to first on landing it might rev up to 90,000.

 

[Nyogtha]

There were coupled compressor-turboexpander assemblies in a cryogenic system designed to recover additional propane, butanes, and gasoline from catalytic reformer off-gas which has a high hydrogen content. You found out really quickly if the combination glycol and molecular sieve drying systems weren't doing the job adequately for example.

 

[Mr Nice]

Originally Posted By: FowVay
These engines don't spin nearly that fast. The low pressure (N1) speed is around 10,000 RPM and the high pressure (N2) speed is around 17,000 RPM. These things are small in size for an airplane engine, although you should see the cute little CF34

I work the CF6 and it's a virtual tortoise in comparison due to the size. It spins around 4800 RPM N1 and 7500 N2.**note: these RPM's are off the top of my head so don't nit pic if they're off by a few hundred.

The FAA issued an emergency AD (airworthiness directive) to have these stage 1 blades inspected in the next 20 days. The airports and maintenance hangars are hopping with NDT inspectors. The inspection is now an ultrasonic on-wing inspection. The blades already get an FPI and ECI during overhaul. Blades are NOT considered critical rotating parts although the disk that they attach to is. Blades are not life-limited either. The initial ultrasonic inspections are going to be on blades that have accumulated 30,000 cycles.


Love your jet engine technical explanations.

How long have you been working on jet engines ?

 

[Yah-Tah-Hey]

Originally Posted By: FowVay
The blade roots have a coating of copper-nickel-indium on the pressure faces. This sacrificial material prevents blade-to-disk contact. The visual inspection that occurs routinely at blade re-lube includes verifying the amount of Cu-Ni-In remaining. I can't quote off the top of my head but rarely is it allowed to have more than 10% of this coating missing.

By reapplying the molydag you are extending the service life of both the disk and the blade. Cu-Ni-In is applied at manufacture and overhaul and Molydag 254 is also applied during manufacture and overhaul. When new the Molydag is cured in an oven in order to ensure proper bonding. Routine maintenance affords only that the Molydag be brushed on and air dry at predetermined intervals such as every 100 cycles.

Another twist to this whole cycle is that once the blade slot dove tails on the disk become excessively worn they will broach the slots and then use shims to take up the slack.

The condition of the Southwest engine will likely never be disclosed. I do know that they turn an incredible amount of cycles on their engines. An AD will be issued very soon for further root inspection of these blades. Southwest just happens to have the highest level of exposure. No matter what the media spills about this you can be assured that this airline plays by the book and does their due diligence at keeping the fleet up to date.
Do you know if they hire Spartan grads?

 

[SEMI_287]

Originally Posted By: FowVay
I don't know,,, if the pilot misses a shift or accidentally goes from 5th to first on landing it might rev up to 90,000.

There's a new idea for a engine, a manual shift geared turbofan.

 

[Shannow]

Nyogtha wasn't saying that the engine in question was 90,000RPM, but in his experience of rotating turbomachinery (including such speeds) that he'd never seen BLS's conjecture of casings taking out an isolated blade.