# Losing Both Engines on a 777

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We know that current twin engines aircraft like a 777 are relatively safe - a chance of losing both engines for unrelated reasons is tiny. The current rate of unscheduled in-air engine shutdowns for the 777 type is 1 event per 250,000 hrs of operation per engine. Ok, I then asked myself the following question: How long do we have to wait to have a 50% chance of witnessing such a rare 2 engine failure on this aircraft?. (Assuming current level of traffic).To answer this question I first used available number of current 777 flights - about 170,000 flights per year. I also guessed an average 777 flight is 10 hrs. in duration. This gave me a probability of about 0.00027 to have a shutdown of both engines on any single 777 flight in a year. But still it does not provide the answer to my original question.I don't want to bore anyone with mathematical details - I actually had to write a relatively simple program to do the calculations. I could not find an analytical formula (I was looking at Poisson's formula but did not find a way to apply it) for what I wanted and otherwise I was facing an impossible task of performing thousands of multiplications. On my laptop it runs a fraction of a second and the program took me only 5 minutes to write.This is the answer: 2548 yearsAnd you might ask - how long for 90% chance - 8465 yearsMichael J.

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The A330 took only about 10 years...

>The A330 took only about 10 years...And only one year for it to happen to a 767... but your anti-european/airbus craze made you forget about it, maybe...And obviously, apart that, what Michal said is right: running out of fuel is not to be considered an "engine failure"...Marco

Actualy, with that Qatar Airways A332, it took only a few days. ;) Honestly, in most cases Airbus and Boeing use the same engine types, so it's a matter of maintenance, or luck, or with the 767, Imperial gallons. In the case of the brand new Qatar A332, it flew through a monsoon, and apparantly drowned the engines. They were restarted within 2 minutes or so, and the plane landed safely. "Landed Safely" - the key phrase.

they ran out of fuel though because of an error in the connection between the fuel lines and the engine, which caused a major fuel leak which was either misrepresented or misinterpreted in the cockpit.That makes it a mechanical failure which due to its location could be called an engine failure, though it was of course due to faulty maintenance.And no, I didn't forget about the 767. I just had no reference data about how long after service entry it took.I may not like Airbus, but that doesn't mean I can't be objective...

G'day Michael,You wouldn't be looking for a job as a public relations manager with an airline by any chance. :-)What I'm advocating is that it is misleading to introduce statistics that includes ifs and buts, on losing engines because in the long run it doesn't matter whether the loss is from related or unrelated issues, mechanical failure (exploding turbines) or an eagle taking a short cut through the engine rather than around it, the net result is the same - loss of engine Just trying to add balance the odds. :-)Cheers,Roger

Listen, I tried to explain but it doesn't get to you. In this case regardless how many engines you would have all of them would shut down. Even if you consider that one of the engines failed because of the fuel line the other did not. If an aircraft flies into a hail storm and loses both engines is another similar case. Never since the day of modern aviation or since statistics were kept no airliner went down because of loss of both engines due to mechanical 'unrelated' malfunctions. I thought what I was talking about was easy to grasp - clearly not for you.Michael J.http://www.precisionmanuals.com/images/for...argo_hauler.gifhttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg

Well numbers like that are being considered when agencies are looking into ETOPS operations (recent drive to increase to 330 min.) - there is nothing misleading about them - they are based on the current data for modern jet engine reliability. What the above numbers only show that frankly with odds like that it makes little practical difference how many engines you have (2 at least), the odds are so small they are dwarfed by all other potential causes - pilot errors, other malfunctions, running out of fuel, weather, terrorism, war, ATC errors, etc. Michael J.http://www.precisionmanuals.com/images/for...argo_hauler.gifhttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg

With the A330 that lost both engines Airbus tried to blame the pilots. However, when they did the airline turned round and said "they went by the book, that you wrote", which kind of shut Airbus up. The pilots were heroes and I believe still hold the record for "deadsticking" an airliner, 89 NM I think it was, and still had to lose speed and altitude when they got there, pretty amazing pilots.Back on topic though, it is very rare even for a single-engined plane to lose it's power, for two engines this goes up exponentially, then again for 3 and 4. Imagine the chances of losing all your engines on an AN225 Mriya with 6 of the things. They must be absolutely infinitessimal.(Spelling?)

a chance of losing both engines for unrelated reasons is tinyI'm not going to pretend to be the aviation safety expert, but from what I've learned over the years, including assisting the recorder in few military accident investigations - unrelated reasons - is about as impossible as stated elsewhere in this thread.That however does not mean the aircraft is beyond the possibility of it happening. Once in 2,548 years can be tomorrow and then not again until 4554 AD.I'd be hard pressed to actually find a case of any incident/accident in the past 20 years where multiple engine failures had totally unrelated causes.Also most cases of multiple engine loss in aircraft I've seen (including a hairy ride and landing at Danang in an EC-121 with both 1 and 2 out) have come down to a sequence of events.The aircrew concentrating on one problem and allowing another problem to develop and result in either the loss of another engine, or all engines - is too common in accident reports.Understand also I'm not blaming aircrews - at times everyone expects them to perform not only significantly above the level of ordinary humans, but above the competence level of a god.Also as stated elsewhere - Airbus, Boeing or whatever really doesn't matter the engine type / manufacturer is more likely to be a commonality than the airframe.

G'day Michael,>Well numbers like that are being considered when agencies are>looking into ETOPS operations (recent drive to increase to 330>min.) - there is nothing misleading about them - they are>based on the current data for modern jet engine reliability.True that modern jet engine reliability has improved over the years, but that is NOT THE ONLY CAUSE (reason) for ETOPS.The push for using these glowing odds is simply a fuel saving ploy at the passengers risk. But they are NOT indicative of the odds that an aircraft may need to be near to an airport after suffering engine failures/shutdowns. To use them for trying to establish ETOPS is misleading.>What the above numbers only show that frankly with odds like>that it makes little practical difference how many engines you>have (2 at least), the odds are so small they are dwarfed by>all other potential causes - pilot errors, other malfunctions,>running out of fuel, weather, terrorism, war, ATC errors, etc.Tonights news. A twin engine Piper had to ditch at sea because only one engine failed. Flying on a single engine it simply ran out of fuel! Cheers,Rogeredit: apologies Michael I used your signature images.

>Tonights news. A twin engine Piper had to ditch at sea because>only one engine failed. Flying on a single engine it simply>ran out of fuel! >Since when was Pipers ETOPS certified?-

G'day,>Since when was Pipers ETOPS certified?That's the point exactly! They aren't, but private flying across the Pacific is fraught with danger.If Michaels figures are used to extend the ETOPS range then sooner or later ( and I'm not talking 8000 odd years) we will be reading about 777's ditching at sea. Cheers,Roger

Doesn't the ETOPS specification require the ability to fly on one engine at FL100 (due to possible depressurization) for the required distance?-

>True that modern jet engine reliability has improved over the>years, but that is NOT THE ONLY CAUSE (reason) for ETOPS.And who said it was? Of coures the main driver for ETOPS is efficiency of twin-engine aircraft. Engine reliability is something that makes it possible.>But they are NOT indicative of the odds that an aircraft may>need to be near to an airport after suffering engine>failures/shutdowns. To use them for trying to establish ETOPS>is misleading.Sorry I don't understand the meaning of that.>A twin engine Piper had to ditch at sea because>only one engine failed. Flying on a single engine it simply>ran out of fuel! Again, I fail to see connection with the topic. This Piper could have had 4 engines and it would make absolutely no difference.Michael J.

>I'd be hard pressed to actually find a case of any>incident/accident in the past 20 years where multiple engine>failures had totally unrelated causes.>Correct. Whether you go back 20 years or 60 years - it never happened. Michael J.http://www.precisionmanuals.com/images/for...argo_hauler.gifhttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg

In the worst aviation accident in South Australia for 28 years, a Navajo had multiple-engine failure crashing into the Spencer Gulf.Although the loss of both engines in this accident seem to be related, there is a small possibility that the loss of the right engine may have been caused by other reasons.* "left engine failed first as a result of a fatigue crack in the crankshaft."* "It is likely that because of the increased power demanded of the right engine after the left engine failed, abnormal combustion (detonation) occurred and rapidly raised the temperature of the pistons and cylinder heads. As a result, a hole melted in the number 6 piston causing loss of engine power and erratic engine operation."Taken from Flight Safety Australia Magazine - January/February 2002 issue

Have a great Day/Night where ever you are! :-wave

http://www.3dflite.com/dac/img/BANNER-soccer.gif Student Pilot - YSBKC152/Tomahawk/Warrior/Archer/Duchess66.3 hrs Total

"I know folks are trying hard to come up with a counterexample - wish you luck."Not trying to come up with a counterexample. I know a Navajo ain't a 777, but multiple-engine loss is multiple-engine loss regardless of it being piston, turpoprop or a turbine.

Have a great Day/Night where ever you are! :-wave

http://www.3dflite.com/dac/img/BANNER-soccer.gif Student Pilot - YSBKC152/Tomahawk/Warrior/Archer/Duchess66.3 hrs Total

If you read "Fate is the hunter" (one of my favorite books) by Ernest Gann-he documents all 4 engines failing on a DC 4A-(they were able to restart them for occasional time periods to get back once they got below 3000 ft.-was a problem with the engines not working at altitude)...An earlier chapter also documents a similar venture with 3 out of 4 engines quiting on a C-54 due to incorrect spark plugs.http://mywebpages.comcast.net/geofa/pages/rxp-pilot.jpg

>>In the worst aviation accident in South Australia for 28>years, a Navajo had multiple-engine failure crashing into the>Spencer Gulf.>>Although the loss of both engines in this accident seem to be>related, there is a small possibility that the loss of the>right engine may have been caused by other reasons.But a Navajo is not ETOPS certified!Marco

G'day Michael,Now go back and calculate the odds of multiple engine failures on an aircraft for ANY reason. They are the true odds that should be considered for ETOPS I can assure you they will be condiderably lower than the odds you are quoting for unrelated reasons. Whenever restrictive controls are set in place there is always a drive by vested interests to whittle away at them.ETOPS was enacted for my interests and as a passenger my safety comes ahead of some engine manufacturers concocted reliabilty figures or airlines bottom line :-)Cheers,Roger

>Now go back and calculate the odds of multiple engine failures>on an aircraft for ANY reason. They are the true odds that>should be considered for ETOPSThey are. And they will be not much different than for a 4-engine aircraft and that's the whole point of this discussion. Once you start looking at certain other types of failures number of engines have little to do with your final odds. Michael J.http://www.precisionmanuals.com/images/for...argo_hauler.gifhttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg

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