Oceanic Long Haul - 2 or 4?
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United did have an engine failure at the PNR of all places so had to keep on truckin' to Hawaii on one engine. They ended up exceeding the ETOPs limit due to 'unforecasted head winds'
Dunno what the FAA did about it all however it would have been a pretty tense trip 3.5 hours on one engine over the Pacific at night!! Bet those blokes were wishing they were in a 747!! They at the moment hold the record for an ETOPS flight which wouldn't be a terribly saught after record to have i'd imagine
Dunno what the FAA did about it all however it would have been a pretty tense trip 3.5 hours on one engine over the Pacific at night!! Bet those blokes were wishing they were in a 747!! They at the moment hold the record for an ETOPS flight which wouldn't be a terribly saught after record to have i'd imagine
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What was the economic argument for putting 4 engines on the BAe146 when everyone else was building 2 engine shorthaul machines at the time (1981)? I can't believe that beancounters didn't dominate that decision.
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I thought the 146 was designed for STOL operations hence it's rather unconventional (in airliner terms) configuration.
On the subject of the United diversion, I am led to believe that SOP demand that following an engine failure in a twin, the commander must divert to the nominated diversion field which will be less than 3 hours away. However, that 180 minute calculation has been made on the basis that MCT is selected. I wonder how many aircraft commanders will be willing to select MCT on their sole engine knowing that it will be at a high power setting for 3 hours? Since many more engine failures take place at high power settings than low settings, surely the commander will mitigate against this risk by selecting a lower setting and opting for a lower cruise speed?
On the subject of the United diversion, I am led to believe that SOP demand that following an engine failure in a twin, the commander must divert to the nominated diversion field which will be less than 3 hours away. However, that 180 minute calculation has been made on the basis that MCT is selected. I wonder how many aircraft commanders will be willing to select MCT on their sole engine knowing that it will be at a high power setting for 3 hours? Since many more engine failures take place at high power settings than low settings, surely the commander will mitigate against this risk by selecting a lower setting and opting for a lower cruise speed?
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When you combine this topic with the lack of fuel reserves highlighted in the Shock horror Nigel has to wait thread,it makes worrying reading.By my understanding on a twin,one engine out means lower cruise altitude therefore higher fuel consumption,if there were any delays at the final destination due to weather or other factors, it seems that it's only a matter of time until the inevitable happens.
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Don't worry too much lasernigel...
The ETOPS discussion is mostly not about the amount of fuel on board, it is about how long you are willing to fly with only one engine left and no other redundancy over the ocean, which is very black and deep at night.
Losing an engine does not automatically mean a higher fuel flow. If you reduce your speed to max range the trip takes longer, but will use less fuel than at a high cruising speed with 2 engines. The effect of a lower cruise altitude is offcourse included in the ETOPS calculation. On top of that, of you reach your (diversion-) destination after two hours of flight with only one engine, you won't have to wait till all the others have left the holding in front of you. I never heard of any ATCO not clearing the runway immediately for an emergncy.
As you are still flying and not on fire or such, you will have some time to discuss to which airport you will fly and check the weather. On top of that, because you need alternate planning minima for your enroute alternates, the weather forecast for those airports has to comply to certain standards, making a diversion to such an airport possible.
P77
The ETOPS discussion is mostly not about the amount of fuel on board, it is about how long you are willing to fly with only one engine left and no other redundancy over the ocean, which is very black and deep at night.
Losing an engine does not automatically mean a higher fuel flow. If you reduce your speed to max range the trip takes longer, but will use less fuel than at a high cruising speed with 2 engines. The effect of a lower cruise altitude is offcourse included in the ETOPS calculation. On top of that, of you reach your (diversion-) destination after two hours of flight with only one engine, you won't have to wait till all the others have left the holding in front of you. I never heard of any ATCO not clearing the runway immediately for an emergncy.
As you are still flying and not on fire or such, you will have some time to discuss to which airport you will fly and check the weather. On top of that, because you need alternate planning minima for your enroute alternates, the weather forecast for those airports has to comply to certain standards, making a diversion to such an airport possible.
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If the 2 v 4 engine debate remains sufficiently alive amongst those of you that fly the things why (as 18 wheeler said) have there been no more new 3 engine designs?
Was there anything seriously wrong with the MD11?
Surely a new 3 engine design would satisfy the bean counters and the worriers and not be too much more trouble to conjure up than a new 2 or 4 engine design.
Was there anything seriously wrong with the MD11?
Surely a new 3 engine design would satisfy the bean counters and the worriers and not be too much more trouble to conjure up than a new 2 or 4 engine design.
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Thanks for your input Pegasus,I added 2+2 and obviously got 5!
But,for instance on the proposed San Francisco - Hawaii 737-800 route,how many diverts are there after PNR?Just interested.
But,for instance on the proposed San Francisco - Hawaii 737-800 route,how many diverts are there after PNR?Just interested.
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How nervous would you be? - You're in a twin over the ocean at night, 180 mins from closest diversion. Both engines have been on the airframe since new and therefore have identical hours and cycles. Suddenly, one engine goes twang as a consequence of a previously unsuspected fatigue problem. You shut it down and then there you are - 180 mins from diversion with one engine remaining which, in every respect, is identical to the one that has just failed and, presumably, is just as likely to suffer the same failure. I bet that 180 mins is longer than a lifetime!
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keendog,
You are not likely to see a three engine design again.
It is rather weight design limited, and a huge compromise over two.
The only real reason the L10 and the DC10 were three engine designs, was that the engine 'technology' was not up to snuff for two.
The TriStar actually began design life as a twin (for a specific request from AA)...and of couse you didn't see any twin-engined TriStars in the AA fleet..RR couldn't produce a big enough engine.
Altho 4 engines are nice to have for long overwater flights, twins win every time on efficiency grounds, so expect to see a lot of 'em on transoceanic routes.
In addition, no matter how many engines you have, if one fails, lower cruise altitudes are guaranteed, at the heavy weights encountered, and additional fuel burn follows in many cases.
Proper planning from the beginning, together with truly sensible enroute alternates are very necessary to keep safety margins adequate.
You are not likely to see a three engine design again.
It is rather weight design limited, and a huge compromise over two.
The only real reason the L10 and the DC10 were three engine designs, was that the engine 'technology' was not up to snuff for two.
The TriStar actually began design life as a twin (for a specific request from AA)...and of couse you didn't see any twin-engined TriStars in the AA fleet..RR couldn't produce a big enough engine.
Altho 4 engines are nice to have for long overwater flights, twins win every time on efficiency grounds, so expect to see a lot of 'em on transoceanic routes.
In addition, no matter how many engines you have, if one fails, lower cruise altitudes are guaranteed, at the heavy weights encountered, and additional fuel burn follows in many cases.
Proper planning from the beginning, together with truly sensible enroute alternates are very necessary to keep safety margins adequate.
I never (ever) buy tickets on trans-Atlantic flights that use aircraft with anything less than 4 engines. This limits my options in terms of airline or flight, however after reading some of the remarks made by the people who actually fly the things, I feel somewhat vindicated. For those that can waive stat's about twin op's and their reliability, this must seem incredibly irrational. There is no substitute for multiple redundancy, if lightning never strikes twice in the same spot, why do insurers increase your car premium when you make a claim - even if the accident was somebody else’s fault?
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Forgive the question, but why is a twin more efficient?
I can understand it being cheaper initially, and I imagine it is cheaper to maintain two engines than four, but is there a significant difference in in-flight efficiency?
Why would four smaller engines not be as efficient as two bigger ones? And would the two bigger engines not need to be significantly over-rated (moreso than the four small) in order to cover for a failure on take-off?
I can understand it being cheaper initially, and I imagine it is cheaper to maintain two engines than four, but is there a significant difference in in-flight efficiency?
Why would four smaller engines not be as efficient as two bigger ones? And would the two bigger engines not need to be significantly over-rated (moreso than the four small) in order to cover for a failure on take-off?
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Java’s Galunggung volcano
multiple engine failures do occur...
http://www.nw.faa.gov/releases/volash.html
We all know this amazing story, but what if this volcanic ash incident happened to a 777 for example?
I totally agree... the more engines the merrier!
http://www.nw.faa.gov/releases/volash.html
We all know this amazing story, but what if this volcanic ash incident happened to a 777 for example?
I totally agree... the more engines the merrier!
Just how is a 777 safer than the 747 if all engines are snuffed out on both aircraft? Same would happen to a 10 engined plane if it flew through volcanic dust.
Anyone out there have the data for 2 versus 3/4 engine returns? Same of shutdowns. Saw it a few years ago, it showed that the ETOPS redundancy actually produced a safer product. It wasn't Boeing derived data either.
Anyone out there have the data for 2 versus 3/4 engine returns? Same of shutdowns. Saw it a few years ago, it showed that the ETOPS redundancy actually produced a safer product. It wasn't Boeing derived data either.
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Ask the 3 and 4 holers what happens when they get a decompression in the middle of the ocean. There are several occasions when they will not have enough fuel to reach a suitable div without either shutting engines down or at least throttling back to idle. At least with twin ops, we have that scenario covered in our fuel planning. It is normally the limiting factor and requires us to carry extra fuel to comply with the planning minima.
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In my airline at least (4 engines only - for the moment!), extra fuel required by the decompression scenario is included in the flight plan. We would not have to shut down engines, or slow down (other than as required by the lower level) in order to make our oceanic diversions.
West Coast - True, if you fly through a volcanic dust cloud there's a good chance that all the engines may quit. But with four engines you have twice the chance that at least one will light up again when you clear it. Remember the BA 747 with Captain Moody all those years ago, they still only got 75% of the engine running after they were well clear of the dust.
javelin - As Scroggs wrote. Our plans cover low-level diversions. It's really only a problem with long over-water flights though, where you have limited options as to where to go.
javelin - As Scroggs wrote. Our plans cover low-level diversions. It's really only a problem with long over-water flights though, where you have limited options as to where to go.