Go Back  PPRuNe Forums > Flight Deck Forums > Rumours & News
Reload this Page >

MAX 737 American Flight 2555 from Miami to Newark Engine Shutdown

Rumours & News Reporting Points that may affect our jobs or lives as professional pilots. Also, items that may be of interest to professional pilots.

MAX 737 American Flight 2555 from Miami to Newark Engine Shutdown

Old 13th Mar 2021, 00:00
  #21 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 65
Posts: 3,196
First off, that failure wasn't supposed to happen - the nacelle should not fail due to a FBO (reportedly Boeing had a fix in the works for the nacelle coming apart - which apparently was delayed because of the FAA paperwork - which should have prevented the nacelle failure in the similar UAL event in Denver).
But more to the point - FBO is a rare event - something like 10-7 per flight (which, BTW, is the same probability number used for an uncontained rotor burst failure). And FBO at cruise is extremely rare - nearly all FBO events are during TO or initial climb. So you're talking an event probability that is way out there - the same sort of probability that an uncontained engine failure will cause catastrophic damage. Yes, it happened - but so do many improbable failures that endanger continued safe flight and landing. The statistics are solid - adding engines doesn't improve safety. Quite simply there are better places to spend money if the goal is to improve flight safety.
tdracer is offline  
Old 14th Mar 2021, 17:56
  #22 (permalink)  
 
Join Date: Apr 2006
Location: uk
Posts: 891
tdracer many of the arguments I have listened to about ETOPS could equally be applied to a case for saying that 1 engine is as safe, or safer than 2. And there are many cases where additional engines don't help, eg running out of fuel, to name the most obvious.

But you contradict yourself by asserting that "after you have two engines, adding more doesn't help safety," and then saying "there is a small but finite probability that a twin engine aircraft will suffer a dual engine shutdown or loss of thrust that turns catastrophic - and the probability gets smaller if you add more engines". Exactly.

It is a fallacy that you increase the chance of a catastrophic failure by having more engines. Apart from related failures (ie fuel starvation, volcanic ash etc) each failure is a random event. The probability of the first failure is the same whether your are flying with 2, 4 or 8 engines, as is the probability of a second unrelated failure which is, as you say, small but finite. I do believe that the small probability of a genuinely random second failure is increased by the fact that one engine has failed, due to a number of factors that are hard to quantify. 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?

The limiting factor on allowable diversion times was, if I recall correctly, the longest time that a hold fire could be suppressed, nothing to do with engine failure probabilities, and maybe that's still the case. I often wondered if that figure has ever been really tested in all conceivable types of hold fire. Maybe it has, maybe it hasn't. That's a problem with quads also, of course!

By the way; "
First off, that failure wasn't supposed to happen". There you go, Murphy strikes again. It wasn't supposed to happen, but it did because it could.
old,not bold is offline  
Old 14th Mar 2021, 19:44
  #23 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 65
Posts: 3,196
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).
tdracer is offline  
Old 14th Mar 2021, 20:36
  #24 (permalink)  
 
Join Date: Feb 2001
Location: Europe
Posts: 1,056
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
CargoOne is offline  
Old 14th Mar 2021, 21:58
  #25 (permalink)  
 
Join Date: Jan 2008
Location: Hawaii
Age: 73
Posts: 45
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.
hunbet is offline  
Old 15th Mar 2021, 02:45
  #26 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Commuting home
Age: 43
Posts: 3,189
Originally Posted by tdracer View Post
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).
Apologies, I understand the wording may have been simplifed. It seem to depend on what is meant by (shown to be) _statistically safer_ in this context. Is it that
- 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.
FlightDetent is offline  
Old 15th Mar 2021, 03:00
  #27 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 65
Posts: 3,196
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.
tdracer is offline  
Old 15th Mar 2021, 03:29
  #28 (permalink)  
 
Join Date: Jan 2013
Location: Seattle Area
Posts: 267
The Kalitta accident was a good way to illustrate your point that the heavy quad canít stand a second engine failure. Those werenít 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 thatís a cascading effect of the first failure. I recognize that wasnít your main point in mentioning that accident.

I donít think Iíve 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.
Dave Therhino is offline  
Old 15th Mar 2021, 11:32
  #29 (permalink)  
 
Join Date: Apr 2006
Location: uk
Posts: 891
Originally Posted by tdracer View Post
............................ engines on quads often don't get as good of maintenance attention.......
What!? (as Oprah would say). Any evidence to back that one up? I don't think it's going off thread to ask the question; it's a factor in the discussion if true.
old,not bold is offline  
Old 15th Mar 2021, 14:32
  #30 (permalink)  
 
Join Date: Apr 2008
Location: Europe
Posts: 82
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.
hoistop is offline  
Old 15th Mar 2021, 17:43
  #31 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 65
Posts: 3,196
Originally Posted by old,not bold View Post
What!? (as Oprah would say). Any evidence to back that one up? I don't think it's going off thread to ask the question; it's a factor in the discussion if true.
I don't have access to current information, but with the same engine on 747s and 767s, the 747 fleet usually had a marginally higher IFSD rate. Now, part of that is you're more likely to do a precautionary shutdown on a quad than a twin, but when you looked at the actual data, it went deeper than that. Also, ETOPS put restrictions on the same mechanic/team doing maintenance on both engines at the same time - rules that did not always carry over to quads (and a significant number of shutdowns are due to maintenance errors).
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).
tdracer is offline  
Old 15th Mar 2021, 18:17
  #32 (permalink)  
 
Join Date: Apr 2006
Location: uk
Posts: 891
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.
old,not bold is offline  
Old 15th Mar 2021, 21:57
  #33 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 65
Posts: 3,196
Originally Posted by old,not bold View Post
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.
I think an unappreciated aspect of ETOPS (or at least underappreciated) is that is caused most of the industry to raise their game - resulting in improved safety across the board. There is the more obvious stuff like aircraft designed for ETOPS with improved systems and redundancy (777 being the first), and operators that conducted a significant numbers of ETOPS flights began maintaining their entire fleet to ETOPS standards - rather than maintaining separate ETOPS and non-ETOPS fleets.
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.
tdracer is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.