Are you implying that the video is not “real info”? I know the titles can be pretty click-baity (which I blame on his production team), but I have always found the actual content of Petter’s videos to be well researched and pretty much sticks to “just the facts”. (But full disclosure, I haven’t watched that particular video yet, just because I haven’t had 40 minutes of free time in which to do it.)
No. I simply do not watch vids for information on any topic. Give me a 1, 10, or 100 page written report and I’m all over it. A vid? Not even gonna click to read the blurb about it.
Clearly a personal foible in our post-literate era. But it’s my foible & I’m holding onto it for dear life.
Well, here’s a news article about the events of concern.
Tl;dr: If the left side CFM LEAP-1b engine of a 737-MAX loses a fan blade, a vibration compensating system will (as an unavoidable side effect) dump the entire forward rotor lubrication (“A”) sump into the compressor flow, rapidly vaporizing multiple gallons of oil into the cockpit-primary AC pack. So the cockpit is rapidly smokebombed with high concentrations of toxic visually-obscuring oil vapor, quite possibly at a time of high stress (takeoff + failed engine response).
“Toxic” in the sense of “potentially lethal in 40 seconds”.
Me too. I do share videos, and I watch some; but if I’m looking for an ‘article’, I hate to open a page and find out it’s a video.
Thank you.
I’m a bit confused about the suggestion upthread that some entity statistically anticipated two of these events every year. That seems to suggest a lot more severe bird ingestions than my recollection of history. Not every birdstrike is into an engine and not every engine birdstrike would be expected to shed a fan blade.
That two events actually happened in one year is not the same thing.
Having said all that, that does seem to be a failure mode with decent probability of a disastrous outcome. Such that prompt redesign should be required by FAA and that any reasonable mitigating procedures should be rapidly put into place. Making bleed-off takeoffs with or without APU as applicable might well be a smart move. It’s certainly a low-ish cost move that can be implemented by all carriers in a matter of days.
Now for the fine print. …
As I mentioned upthread, assuming a 737 w no pre-existing malfunctions, the APU can be used to power the air conditioning / pressurization system up to 17,000 MSL. Which is roughly 9,000 AGL above the highest altitude airports that 737s operate may to/from.
Most large birds are high altitude capable birds. You can find eagles, hawks, buzzards, geese, etc. at 10,000 feet or more. They’re more common down lower, but they are up high too. Unlike e.g. sparrows & pigeons.
So at what altitude during climb-out do we stop using APU bleed and switch to engine bleed if a large birdstrike is going to be assumed to lead directly to a high criticality cockpit or cabin smoke/fumes event? Do we do the same thing on descent?
Note that switching to APU bleed removes significant redundancy from the total HVAC / pressurization system and will increase the incidence of loss of cabin pressure incidents. The good news is most of them will begin at relatively low altitudes where lasting harm to even frail passengers is unlikely.
If the airplane is dispatched with a generator out of service the APU will be supplying electricity too and can only supply bleed air up to 10,000 MSL, which may be as little as ~1500 AGL versus a high altitude airport.
I can see FAA choosing to direct Boeing to develop an interim procedure for bleeds off takeoffs as the norm. I can also see them directing CFM to solve the oil dump problem. I could also see them deciding the rest of the opened cans of worms make it easy to justify standing pat on procedural changes while directing CFM to come up with a hardware fix. In any case, any hardware fix will take several years to certificate then fully retrofit into the fleet.
Be interesting to know FAA’s actual calculations and rationale. By design, NTSB doesn’t really include practicality in their safety recommendations. They’re whole thing is “In an ideal world, you should do …”. FAA is charged with adding practicality into the mix. Assuming they haven’t all been laid off.
An interesting larger question is how common these fan hub Load Reduction Devices are on all sorts of turbofan engines & airplanes. And why / how / whether the CFM LEAP is different in having this oil dump consequence? Or do they mostly all have the same issue, and the MAX is just a very unlucky machine to have had two incidents in rapid succession?
I know I don’t know.
Well, that’s the punchline you don’t see in the article Iinked, but is the reason Mentour did the video.
The FAA literally opted to do nothing. No directives, no negotiation with Boeing, or CFM, or the airlines. There is no rulemaking in response to this information.
Apparently it’s good enough that Boeing issued an FCOM bulletin saying “don’t forget to put on your mask while you work through this crisis.”
Which leads to the question of whether that external inaction was a deliberate result of legit analysis, or just the whole problem being ignored by whichever department ought to have dealt with it. Or being told to ignore it. Or being overtasked and they’ll get to looking at the situation next year when they get around to it.
Again I know I don’t know. But that is a question worth getting a real answer to.
In deference to @LSLGuy’s foibles, here is a transcript of the video.
Here is the passage in question, which comes about three-quarters through the video:
And finally, the sixth recommendation required Boeing to reassess the likelihood of an LRD activation as they had stated during certification that they expected maximum one event every year.
But those two events had happened nine months apart, which might be a fluke, but might also not be.
I found one of Mentour’s media sources about the FAA no-decision.
FAA’s own technical investigators recommended both SW tweaks (to automatically recognize LRD activation and shut down bleed from the affected engine using a pre-existing emergency bleed control system) and procedural preventative measures (not using left-side bleed during takeoff operations, since both incidents were below 900’ AGL during climbout).
That certainly seems to be a possible smoking gun for political interference. Although whether the politics are FAA-internal or Boeing bullying the bureaucracy is TBD.
One of the problems with widespread government decay is that even when something is done for legit reasons, the likely reaction by observers is to assume it was done for evil reasons.
Cynicism is a vile and corrosive attitude. But if you you live in a world operated of, by , and for cynics, pretty soon you too need to adopt that attitude in order to survive with sanity intact.
I’m not saying the USA, the FAA, or this decision are necessarily there now. But it seems things are flowing in that direction. Uggh. Glad I’m out of the biz.
Lily Tomlin said that the problem with being cynical is that, no matter how cynical you get, it’s impossible to keep up.
(Or something like that. There are lots of slight variations out there.)
Maybe my stats is rusty, but if the mean time between events is expected to be 12 months, having a pair of events happen 9 months apart is not that unusual.
The other thing about “max 1 event/year” is that’s presumably based on what Boeing expected the total MAX (heh) fleet size to be. Which fleet is now about 1/4th the hoped for final production run.
I still find the idea of 737 engines shedding fan blades bad enough to trigger LRD even annually to be very high versus my intuition. Just based on other airplanes I’d expect more like one blade loss to all causes per 3 or 5 years.
LSL thanks for you input on this. I still don’t fully understand the oil dump. Does the fluid dampen the out-oz balance issue or is it it flooding the bearing assembly? It would be interesting to see how a broken blade is dealt with in other engine designs.
I’m sorry, but ‘Whiskey Dick Mountain’ is funny.
I believe the idea is simple. If the whole fan rotor is unbalanced enough and is flailing around in there badly enough, the oil containing area around the forward fan shaft bearing breaks open from the mechanical stress from the flailing. All the oil drains out and real soon the not-lubricated bearing drags the fan to a slower non-harmonic RPM. Or seizes the fan rotor completely. Either way the problem of containing a madly flailing out-of-balance fan is solved without needing to add 1,000 lbs of armor steel around the outside of the fan to hold it in.
But where does all that deliberately leaked oil go? It should go harmlessly overboard. If instead it goes directly into the bleed air feeding the HVAC system and ultimately into the aircraft interior that’s bad. Very bad.
As to other engines …
It appears from further reading that some engines have similar auto-seize systems. Others do the up-armoring instead. There may be other ways to handle radical fan unbalance too, but I don’t know what they are. As fans have gotten bigger and have also gotten fewer but larger blades, the imbalance caused by a single blade loss is much greater than it was back in the lower-bypass small-blade days. Which makes the imbalance problems worse and explains why this issue hasn’t been much in the news from back in the '70s or even the early 2000s.
Here’s a face-on pic of the NG & MAX versions of the CFM56. Differences between the Boeing 737 MAX and Boeing 737 NG engines| Instagram. You can readily see there are fewer larger blades on the MAX version. Making the blade-off imbalance problem inherently worse.
Here’s an interesting question about this engine specifically:
The CFM56 LEAP is available in three models. The -1A for Airbus A319/320/321 NEOs, the -1B for Boeing MAXes, and the -1C for COMAC C919s. Very clever naming convention. Anyhow, I wonder how specific this issue is to the -1B version? And if it is, how is the -1B different from the -1A & -1C? And if they are the same in this respect (as I suspect they are), what does Airbus (or EASA) think about this risk as it applies to their rapidly growing NEO fleet?
A lot of it comes down to airframe integration. Bleed system design and operating practices might make the Airbus variants more resistant, but AFAIK we haven’t seen a blade-loss incident/LRD trigger in an Airbus Neo aircraft yet, so no hard evidence.
As to the basic difference among the LEAP variants, Wikipedia has a table with side-by-side comparison:
Agreed. The high-level diagram of one bleed system is a lot like another. But the devil (or angel) is in the details.
The gross difference between the -1A & -1B is the -1B has a smaller diameter fan to fit with the 737s low sitting height. Which may have necessitated broader-chord blades so a blade-off incident is a bigger deal. Or the specifics of the LRD design means the -1A dumps the oil mostly around the combustor flow path rather than into it. All we know is that we don’t know.
This entire conversation is about the continuing airworthiness process. The fact that the FAA determined “no immediate action” was needed does not at all imply that no action will ever be done. A risk assessment based on event probability and hazard was conducted and the conclusion is that the fleet doesn’t need to be grounded or implement a change before next flight. Either CFM or Boeing (or both; one owns the engine type certificate, the other owns the airframe/integration one and it’s not clear to me where design responsibility for this issue lies) would have presented this risk assessment, and a corrective timeline to find a permanent fix, and the FAA has accepted that.
The FAA is NOT the designer, they do not lead the process here. The applicant has the responsibility to provide a plan to update the design/operation of the engine and execute the certification process for that design change. Then, the FAA would mandate that specific change as a fix to the issue, and that’s where “rulemaking” as mentioned in the article comes in; the issuance of an airworthiness directive is an act of law.
As for the “once a year” assessment; these things come out of the compliance to standards for safe function and operations. They are usually expressed as a probability of an event per flight hour, and that probability has to be various levels of unlikely depending on the severity of the event. It’s possible that the probability was miscalculated, or some assumptions were invalidated by the actual events; this is also likely being reevaluated as part of the continuing airworthiness process to bring the design back into compliance.
Much of the underlying work and information/assumptions being discussed here will never be made public. Some context will be publicised in the AD rulemaking, but the risk assessment data is generally proprietary.