MAX 737 American Flight 2555 from Miami to Newark Engine Shutdown
If's not a fallacy. When you go from 2 to 4 engines and double the number of engines, you double the chance that there will be a catastrophic engine failure (actually its a little worse than that because engines on quads often don't get as good of maintenance attention). That increase is greater than the decrease you get in the probability that you'll have multiple engine thrust loss that turns catastrophic. No contradiction - just basic statistics.
That's not the case when you go from 1 engine to 2, but it is when you go more than 2...
Or to put it a little differently - the 767 and 747-400 were designed with roughly the same level of technology and safety, but the 767 (and 757) are statistically safer than the 747-400 (by roughly a factor of 2).
That's not the case when you go from 1 engine to 2, but it is when you go more than 2...
Or to put it a little differently - the 767 and 747-400 were designed with roughly the same level of technology and safety, but the 767 (and 757) are statistically safer than the 747-400 (by roughly a factor of 2).
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Our world is conducting ETOPS operations for about 40 years now and there was no single accident caused by this so far. It may happen one day but if you take into account how many flight hours were logged in during those 40 years, it leaves no space to doubt regarding safety angle. One of US majors did even overshoot the max diversion time due to the headwinds over mid Pacific many years ago, flying over 3 hours on one engine before landing on Hawaii. What else is need to be discussed here?
ps and no, Air Transat Azores glider does not count in here, with the same circumstances applied, it would be the same outcome with 747 or 340
ps and no, Air Transat Azores glider does not count in here, with the same circumstances applied, it would be the same outcome with 747 or 340
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Not sure you are debating ETOPS. This was caused by a maintenance error when an AMT incorrectly installed a lube unit scavenge screen.
It does not count against ETOPS and It's why 2 AMT'S are required when working on both engines or only one engine is done during a layover and the other is scheduled on a different date.
It does not count against ETOPS and It's why 2 AMT'S are required when working on both engines or only one engine is done during a layover and the other is scheduled on a different date.
Only half a speed-brake
- the number of IFSD over (say 10 k) departures was less on the 75&6 compared to the 747?
There are other metrics to view an IFSD.
- the number of events where 50% thrust loss resulted from an IFSD / (10k departures) (menitoned already)
and
- the number of events of IFSD where the resulting configuration was 1 (single) engine away from total loss of propulsion / (10k departures)
Okay, now the last one is clearly tailored to drive a certain point which had been already disproven by the decades of catastrophy-free twin jet operation. It's recognizable spin doctoring. Saying "the 767/757 ended up statiscically 2x safer than the 747 of equivalent technical design" - - that is equally awful. I remain convinced the bolded metric is a reasonable measure. It takes more bullets to hit more hares, and more luck to take down 4 in sequence than 2. P(n) = p^n.
The disagreement extends against arguments proposed at post #16, all of them to some extent are wagging the dog. To paraphrase, the classical mistake of supporting a good cause with weak examples and hollow logic.
For instance, #16 mentions finite probability of engine fire turning catastrophic (and the suggestions 4 installed increases exposure to the risk). Over the decades while ETOPS / LROPS existed, there was not any. See the lucid post number #21 saying _that (other discussed) failure was not supposed to happen_ and that's agreed. Same needs to apply to an uncontained rotor failure used to create a (not so) convincing probability calculation at # 16.
Nicely demonstrated with the AUA in-flight reverser deployment. Freak (uncontained by design at the time - absolutely love your insights!) failure mode where a fault on one engine takes down the whole ship. With that it certainly applies - having 3, 4, 8 increases the probabilty. That is mathematically valid but no longer relevant as it wouldn not happen again.
A conspiracy theorist would say this all reaks of groupthink and cherrypicking / modelling the probability equations for a pre-determined result. Perhaps in an era when launch of the T7 in twin configuration needed quasi-scientific support? I'm glad they did!
(personally I fly a twin and used to be rated on an ETOPS-180 one too. The marketing campaign 4engines 4the long-haul from a certain manufacturer to battle the T7 seizing her rightful place was pure hypocrisy)
Arcing over towards the dramatic now: in case of a complex failure, is a 2 man-crew safer than a 3 man one because there is less humans to make mess of it? I know, I know ...engines don't correct each other.
and a three-captain cockpit is a recipe for a disaster! 
Ooops, not so much of light relief. Stay healthy everyone.
Last edited by FlightDetent; 15th Mar 2021 at 03:22.
Sorry FlightDetent - I was simply referring to the hull loss and fatal hull loss accident rates. Nothing to do with engines specifically. Granted, a very simplistic argument - but if more engines made the aircraft safer, then one would expect that quads and tri's would have better accident rates than twins - and that's simply not the case.
Although shutdown and loss of control rates are tracked by operational hours and cycles, the fact remains that most engine failures occur early in the flight - takeoff and initial climb. Failures at cruise are but a small subset of the total numbers.
The loss of 50% thrust on a quad - particularly early in the flight - can be catastrophic - quads are not designed for that. In fact the most recent accident I can recall which was the result of multiple independent engine failures was a 747F. Specifically - roughly ten years ago - a Kalitta 747F suffered a major engine failure during takeoff (turbine failure) - the pilot apparently advanced the remaining engine throttles, which prompted a second engine to fail. They didn't make it.
Although shutdown and loss of control rates are tracked by operational hours and cycles, the fact remains that most engine failures occur early in the flight - takeoff and initial climb. Failures at cruise are but a small subset of the total numbers.
The loss of 50% thrust on a quad - particularly early in the flight - can be catastrophic - quads are not designed for that. In fact the most recent accident I can recall which was the result of multiple independent engine failures was a 747F. Specifically - roughly ten years ago - a Kalitta 747F suffered a major engine failure during takeoff (turbine failure) - the pilot apparently advanced the remaining engine throttles, which prompted a second engine to fail. They didn't make it.
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The Kalitta accident was a good way to illustrate your point that the heavy quad can’t stand a second engine failure. Those weren’t independent failures, though. The first failure caused the pilot to increase the power above limits on the remaining tired engines as you said, causing the second failure. Strictly speaking that’s a cascading effect of the first failure. I recognize that wasn’t your main point in mentioning that accident.
I don’t think I’ve ever heard of any instance of two or more truly independent engine failures on the same flight in the last 40 years. I could be wrong though.
I don’t think I’ve ever heard of any instance of two or more truly independent engine failures on the same flight in the last 40 years. I could be wrong though.
Last edited by Dave Therhino; 15th Mar 2021 at 03:39.
For example; if the failure is the result of a maintenance error because the mechanic was tired, cross and under pressure, did that mechanic also work on the other engine on the same shift, and sign off both tasks?
Since quite some time it is prohibited that same mechanic performs same task on both engines or all 3 hyd. systems etc. (critical systems).It was introduced on ETOPS airplanes, but it is (should be) a norm now for all airplanes in Part-145 maintenance. This policy was followed in several maint. organizations I was dealing with in the past.
Since quite some time it is prohibited that same mechanic performs same task on both engines or all 3 hyd. systems etc. (critical systems).It was introduced on ETOPS airplanes, but it is (should be) a norm now for all airplanes in Part-145 maintenance. This policy was followed in several maint. organizations I was dealing with in the past.
Also, some operators (note the disclaimer - I'm not saying this is universal) didn't pay as close of attention to things like EGT margin and vib limits on quads (hence the previously mentioned Kalitta event).
trdracer I'll buy most of that, and I'm already saying 10 Hail Mary's for forgetting the rule about having different teams work on each engine of an ETOPS aircraft.
It's a discussion that's going nowhere, you have your very valid views and I have my reservations. Like, for example, that specific rule (different maintenance teams). Why only ETOPS? If a potential cause of error is one team working on both engines, surely passengers and crew in non-ETOPS aircraft are entitled to having the risk eliminated on the aircraft they are sitting in? To widen the argument, the inference to be drawn from most of the regulations for ETOPS is that non-ETOPS aircraft have a lower standard of maintenance. That cannot be acceptable.
It's a discussion that's going nowhere, you have your very valid views and I have my reservations. Like, for example, that specific rule (different maintenance teams). Why only ETOPS? If a potential cause of error is one team working on both engines, surely passengers and crew in non-ETOPS aircraft are entitled to having the risk eliminated on the aircraft they are sitting in? To widen the argument, the inference to be drawn from most of the regulations for ETOPS is that non-ETOPS aircraft have a lower standard of maintenance. That cannot be acceptable.
But it goes deeper. For example, in the ramp-up to initial ETOPS (EROPS back then), Boeing started looking at the overall shutdown statistics and discovered that a many of those shutdowns were due to known causes with identified fixes. Many operators simply didn't bother to incorporate known fixes - figuring it was cheaper to simply accept the occasional shutdown. Boeing put together a presentation that pointed out just how much each in-flight shutdown cost the operators - not just the direct costs of a broken engine, but all the indirect costs of fleet disruptions, loss of use, remote engine replacements, etc. In short, a shutdown could easily cost the operator over a million dollars (and that in 1980's money) - it was cheaper to prevent the shutdown than to deal with it. After the operators got the message, shutdown rates started dropping dramatically such that now days shutdowns due to known causes with readily available fixes are fairly rare.
NWA SLF
I find it interesting? (alarming?) that this is the third flight that my tiny brain can remember where the rostered crew were overwhelmed and had to use the assistance of jump seat riders or passengering crew to keep ahead of the airplane. UA232, UA1175, QF32
I find it interesting? (alarming?) that this is the third flight that my tiny brain can remember where the rostered crew were overwhelmed and had to use the assistance of jump seat riders or passengering crew to keep ahead of the airplane. UA232, UA1175, QF32
Mistrust in Management
Chris 2303,
It is a case of using all resources available to you in a sensible manner. If a qualified crew member is sitting on the jump seat you would use his/her eyes and ears rather than taking the F/O (or Capt) out of seat - after all such a jumpseater could have been the person rostered to fly with you but happened not to be on that particular day.
It is a case of using all resources available to you in a sensible manner. If a qualified crew member is sitting on the jump seat you would use his/her eyes and ears rather than taking the F/O (or Capt) out of seat - after all such a jumpseater could have been the person rostered to fly with you but happened not to be on that particular day.
exeng
My point was more what if there was no additional assistance available. Would Al Haynes have got the airplane down relatively safely if it was just him, the FO and the FE
My point was more what if there was no additional assistance available. Would Al Haynes have got the airplane down relatively safely if it was just him, the FO and the FE
Check Airman
No question that using available competent resources is good. The real quest is whether the jump seater was a critical resource. Would the captain and FO alone been able to handle the non normal situation successfully? I realize professional pilots are reluctant to admit they could not. But there are some examples to the contrary.
The issue though is not pilot competence, but aircraft design and whether it is good enough, safe enough for two pilots to handle the potential nonnormals.
No question that using available competent resources is good. The real quest is whether the jump seater was a critical resource. Would the captain and FO alone been able to handle the non normal situation successfully? I realize professional pilots are reluctant to admit they could not. But there are some examples to the contrary.
The issue though is not pilot competence, but aircraft design and whether it is good enough, safe enough for two pilots to handle the potential nonnormals.
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I've been retired for 12 years - I don't know what today's processes are. Nacelle failing - would not Boeing doe a DFMEA on nacelle if they found deterioration from years of use, then go to the FAA explaining the urgency? Or is the FAA a roadblock to fast response? I have difficulty listening to experts say the FAA should have caught issues. Being an engineer for 47 years going through design process developments over 5 decades, I cannot fathom how inspectors are supposed to know more about the design and function than the crew designing. My second cousin once removed, who began his career with Boeing in the 1940's and retired after doing finite element analysis on the B-2 in the 1990s, reminisced about how our 2 industries - aviation vs automotive - weren't all that different although his team needed to do a lot more explaining to the people overseeing the project about what they should be looking for. Automotive a lot more reactive. In the nacelle failure incidents, I would foresee a process like finding and analyzing a problem, producing the documentation to the FAA recommending prompt repair. Yet the need to avoid statements or even inferences that if we don't make this change, people are going to die (Applegate memorandum). Living outside Senlis, France, I visited the DC-10 crash site many times to refresh the lesson of how engineers can screw up, assembly and maintenance can multiply the screw up, and even when a pilot like Bryce McCormick tells you that you have a big problem you fail to respond. And even worse sitting on a witness stand reviewing accident pictures when you've been trying to twist arms to implement a change and due to bureaucracy, being forced to defend.
