FAA Statement on Pratt and Whitney Engine Emergency Airworthiness Directive | Hacker News Reader

FAA Statement on Pratt and Whitney Engine Emergency Airworthiness Directive

faa.gov

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This is a video explaining the (contained) engine failure, by blancolirio (Juan Brown) a 777-300 pilot. He commented to expect an Emergency Airworthiness Directive, and there was.

https://www.youtube.com/watch?v=jh4727krwH4

This kind of directive where they won’t let the plane fly again without an inspection is pretty unusual and disruptive. The planes could be at airports all over the world, and the carriers may have to scramble to find people who can do inspections in all those places, plus have parts ready for any that fail inspection. I bet a bunch of flights have to get cancelled or delayed. Usuallt these emergency directives let you comply over a period of days which reduces the operational complexity a lot - you can get it done at your depots, plan out downtimes, and sequence the inspections and repairs so the shop doesn’t have 10 airplanes waiting in line at the same time for the inspection.

It's not that disruptive. The planes affected are a minority of Boeing 777 models, most of these planes are already idle due to the pandemic, and many spare planes of comparable capabilities are available.

https://www.wsj.com/articles/boeings-777-problem-is-no-max-1...

"The affected 777s are the kind of big, old jets that airlines have kept in storage during the Covid-19 crisis. Out of 127 in operation, according to Cirium, 67 were already parked."

There are ~1450 Boeing 777s worldwide, mostly using GE90 engines, including 250 idle ones. The GE90-equipped planes are also generally more capable than the ones with PW4000s, and suitable for longer flights.

Agreed this is unusual. The airlines could likely send inspection teams with appropriate equipment to the airport they are presently at. It is also probable the FAA would issue "ferry permits" to fly the jets to a maintenance base.

United Airlines and probably some other 777 operators fly cargo-only some flights in those aircraft, since the pandemic restrictions started. This would give operators some flexibility to minimize the number of cancelled flights.

For airlines like United Airlines, they fly both 777-200 and 777-300 aircraft. The United Airlines 777-300 aircraft fly with GE90 engines, which are not grounded.

Thanks this was a great follow up. I hadn’t realized it was only a small fraction of the 777 fleet that had these engines

A single engine is 25$ million dollars on a 777. Not exactly something they want to push till its limits on inspections

I disagree with everything you said.

This is a serious problem, and airliners only land at airports with facilities, and engines are falling out of the sky. Sounds like a reasonable AD to me.

https://www.ainonline.com/aviation-news/air-transport/2021-0...

Source: commercially-rated airplane pilot.

Has it been reported how many cycles it had been since the last inspection for the plane which went down?

What do you mean by "plane which went down"? The usual meaning of this slang phrase is to crash. I'm not aware of any crashes related to this directive, only several engine blade failures that didn't result in crashes.

So, if I'm parsing this correctly, this is a requirement to immediately do a one-time inspection that's normally done periodically anyway.

I'm all for safety, but this has a vibe of "Something must be done! This is something... so it must be done!"

There's an existing inspection period of every 6,500 takeoffs and landings[1]. The expectation is that it would take sufficiently long for a detectable flaw to turn into a dangerous fracture that this would be sufficient to notice it. But, given this failure (and presumably also because of the 2018 one), that assumption appears to be untrue. Checking all of them now and comparing any discovered defects to the number of cycles since they were last checked should allow a recalibration of how frequent checks should be (or, if there's an indication that flaw propagation is significantly faster than anyone expected, potentially stronger measures)

[1] My understanding is that it's based on cycles rather than flight time because takeoff is the part of flying that puts the most stress on the blades - spending 10 hours in cruise isn't much worse than spending 2.

Or alternatively, the data might show that 10 hours in cruise IS much worse than 2, and just scheduling on cycles isn't sufficient (obviously they would have flight time data available as well to make that determination).

One reason why turbines are much more reliable than engines is very few parts are ever accelerating. Once the turbine has spun up everything is rotating in unison unlike a crankshaft for example that is constantly changing direction / acceleration

They're demanding inspections to collect more data, and will revise the inspection interval if deemed necessary.

Turbines are designed so that fan/blade separation failures are contained within the engine casing. Uncontained failures are considered a really big deal, because turbine blades carry a shitload of energy, and whether the blade shoots off into the distance or shreds a wing is essentially luck.

The FAA's response to this (uncontained) turbine failure is typical and expected.

Edit: Apparently this may have been a contained failure. See child comments for details. Leaving the text above alone for context.

Yeah i can’t see how the parent comment is framing this as bureaucracy. This seems like a solid move for relatively little risk to gather much-needed data. I’m glad the FAA is at least trying. This is their purpose.

> whether the blade shoots off into the distance or shreds a wing is essentially luck

The blade shoots off radially. Critical equipment is not located radially to the turbine blades. Critical equipment is also not located outboard of the engines.

(Interestingly, Boeing learned in WW2 not to run electric wires through conduit. A hit on the conduit would take out all the wires in it. But if it was just a bundle of wires, nicking a couple with shrapnel wouldn't affect the others.)

I'm very impressed that modern engines can contain a turbine burst while still being light enough to fly.

While there is no component critical to the engine located radially to the blades, there are other things, like wings and passengers.

The wings have redundant structure and will survive. The passengers are likely why there was a push to contain the blades. I don't know when they finally figured out how to do it, but it's an amazing achievement. It's all part of airliners evolving to be safer all the time.

Note that the same problem exists for propeller driven airplanes. I recall one incident where a prop passenger plane was crossing the Pacific when the propeller assembly came clean off. It sliced its way through the fuselage like butter, screwing up the control cables in the process. The pilots got that bird home by the skin of their chinny chin chins.

If you look on the engine, there is a brownish kevlar sheet that is designed to actually contain the blade. The cowling is not part of the testing process for broken fan blades and is not on the test engines.

Ah, kevlar! The same thing put in bulletproof vests. That makes sense. Thanks for the info!

Consider the DC-10 which had the 3rd engine in the tail. One day, the compressor came apart and cut the lines to all three hydraulic systems. The lines drained out, and the pilots had to fly it back using variable engine thrust to control the airplane. They still lost a third of the passengers on landing, but it remains an incredible display of piloting skill that there were any survivors at all.

Slinging the engines under the wings makes it much easier to design the aircraft to be resistant to turbine burst. Modern airliners are now also designed to not lose the entire hydraulic system if a line gets severed (check valves are used).

If Boeing really learned from that it wouldn't have run redundant wires in the same bundles...

I don't know to what extent redundancy was there in WW2 aircraft.

Doesn’t the redundancy show they learned something?

This looks like it was a contained engine failure, even though the cowling fell off. A portion of a fan blade was embedded in the containment ring and the other damaged blades is missing but probably went out the front, slicing the cowling on its way.

https://www.flickr.com/photos/ntsb/50971339066/in/album-7215... does not look contained.

You can't tell from that picture, the damage could have been sustained from the cowling. There is speculation that the damage is from a fan blade but that has not been determined yet. The video of the engine doesn't show any corresponding damage on the side where any fan blade could have exited either.

That's fair. I assume the logic here is that a dislodged cowling or other external engine paneling is traveling at a relatively low velocity when it makes contact with another part of the plane, compared to a fan blade which, if successfully ejected from the engine casing, would be traveling at a very high speed?

Cowling is not designed to hold the fan blades. There is a brown kevlar sheet around the fan that keeps the shrapnel in

Oh, so this is what my initial source was talking about. I guess we'll have to wait for the final NTSB report.

I can't quite tell how far back this is, but it's possible that the failure was contained, but the blade still departed out the back at an angle, and then hit the aircraft further back along the fuselage.

That's a composite fairing that just smooths out the join between the wing and the fuselage. It wouldn't take a lot to do damage to it, so a chunk of the cowling is pretty plausible here.

All of this is true except the assertion this incident is an uncontained failure. There's no evidence it was uncontained. Parts exiting the rear of the engine is a contained failure.

http://avherald.com/h?article=4e35503b&opt=0

I only took a quick look, and this source doesn't seem fantastic, so perhaps it's wrong, but anyway... here's my source [1]:

> Engine failures are defined as contained or uncontained. When engine debris leaves the engine, it is an uncontained engine failure. There appears to be a tear in the rear of the fuselage possibly from a fan blade strike. If this is the case, UA 328 suffered an uncontained engine failure.

Edit:

Yeah okay, after looking at the video in your link, I agree that it appears contained.

[1] https://www.travelcodex.com/united-flight-328-boeing-777-eng...

It's considered an uncontained failure if debris leaves the engine through a hole that didn't previously exist - if it falls out the back (or manages to bounce off the containment structure and exit the front), that still classifies as contained. Obviously the difference to people on the ground is pretty semantic[1], but the assumption is that a contained failure should have very little chance of putting the aircraft at risk.

[1] Well, as long as the failure doesn't result in an entire plane landing on their neighbourhood instead of just a few parts

Then why dont the test engines for broken fan blades have the cowling installed?

The apparent failure is in this specific component and looks like metal fatigue. This inspection would detect metal fatigue in that specific component. It's the obvious place to look.

It may be that they don't find anything. Coincidences can happen, if you fly enough jet planes, enough times, sooner or later something like this will happen. Or it may be that this inspection finds one or more further engines with unexpectedly degraded compressor fan blades. That gives them a pattern on which they can base a subsequent investigation, while also keeping passengers safe.

Yes, it's something that's already done at intervals. The implication is that maybe that interval is too long. Also from TFA:

Based on the initial results as we receive them, as well as other data gained from the ongoing investigation, the FAA may revise this directive to set a new interval for this inspection or subsequent ones.

There's also the possibility that the usual inspection shop was doing a bad job of applying its standards with the necessary consistency and rigor, and that new inspections after engine explosions might see them paying more attention.

See this interesting article on the specifics of the P&W fan blade inspection shop and the process, which the NTSB previously concluded in summer 2020 has hidden behind the label "new and emerging technology" for far too long, avoiding the scrutiny which might make it more reliable: http://aerossurance.com/safety-management/ndi-failures-b777-...

Possible, but less likely since this has now happened 3 times, on different (but otherwise basically identical planes) in an ~18 month time span

> this has now happened 3 times, on different (but otherwise basically identical planes) in an ~18 month time span

Wouldn't that make it more likely that there is some systemic cause, such as a flawed inspection process?

But "periodically" means every 6500 takeoffs and landings.

That seems like an awful long time between inspections. I don't know how often international flights takeoff and land, but the interval might be decades.

The jet engines on the ME-262 had a service life of 20 hours. The service life of the airframe was so short they didn't even bother painting them.

My dad's B-17 was scrapped after 30 some missions for being flying junk, or around 300 hours.

For comparison, the Boeing 757 was designed to fly around 65,000 hours, for comparison. A car is designed to run for 3,000 hours or so. Your car is very poorly made compared to an airplane :-)

I would think an inspection interval should be shorter than an overhaul interval. But I don't know how they do it.

Uh, we also don't overhaul car engines every several thousand hours. That comparison is basically useless.

After several thousand hours of work a car engine will have to have a lot of stuff replaced or serviced. Probably only the block, head, pistons and shafts will remain.

Story of the last 11 months.

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