rabenschlag
Posts: 1012
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Why No Single Engine Jet?

Wed Jul 31, 2002 9:54 pm

with improved reliability of jet engines, is it conceivable that one day there will be a single engine jet? like a 777 with only one powerful turbine located in the rear of the fuselage?

 
gr8slvrflt
Posts: 1452
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RE: Why No Single Engine Jet?

Wed Jul 31, 2002 10:04 pm

I think it is probable but not for quite some time.
I work for Southwest, but the views expressed are my own and do not necessarily represent those of Southwest.
 
pmk
Posts: 609
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RE: Why No Single Engine Jet?

Wed Jul 31, 2002 10:07 pm

Well the FAA is not going to allow it for a while. I will say that there is a business jet called the Visionaire Vantage that is still undergoing certification that is a six seat exec jet with only one P&W engine. Supposed to be certified for part 135 OPS.

Peter
 
MD88Captain
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RE: Why No Single Engine Jet?

Wed Jul 31, 2002 10:58 pm

Single engine jet? With passengers? Not for this pilot. Yes, they are reliable, but not 100% reliable. They quit every so often, like 2 days ago on the DAL 757 coming out of SNA. Ask those guys if they want to fly a single engine passenger jet. Flying single engine/single pilot while strapped to a Martin Baker ejection seat is acceptable risk for many thrill seekers. But a single engine passenger jet is just asking for death and destruction.
 
707CMF
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RE: Why No Single Engine Jet?

Wed Jul 31, 2002 11:24 pm

One thing is sure, no ETOPS certification for such a plane  Wink/being sarcastic
 
backfire
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RE: Why No Single Engine Jet?

Wed Jul 31, 2002 11:49 pm

Civil aviation safety is based on a fundamental premise: redundancy of critical systems, regardless of reliability.

Single-engined commercial flights? IMHO it'll be allowed the day after the engine is designated a non-safety-critical part of the aircraft. Work out for yourselves how long that'll take...
 
transswede
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 12:00 am

With so many proponents for twin-jets over quad-jets in this forum, shouldn't a single-jet be even better?  Big grin
 
N79969
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 12:03 am

There will not be a single engine transport aircraft in the foreseeable future. No way the FAA or JAA would approve that.
 
rabenschlag
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 12:14 am

now that so many of you find it to be unlike, just think about the following two thoughts:

a) it's not about redundancy per se, it's about probability of a complete loss. i think it is at leas conceivable that one will be able to build an engine that is less *likely* to fail than two engines at a time (e.g. two first generation jet engines).

b) there are many one engined prop's and nobody cares. there are even large ones that may carry 6 pax or more (like the pilatus).


sooooo, perhaps its not an obvious development but not impossible, or is it?

thanks for your input, r.

 
N79969
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 12:20 am

I think 6 seats is still general aviation and not transport category. The engines used on the 767,777, and the 330 have reached a point of near 'fail-safe' meaning that they cannot really become a lot more reliable than they are already. In spite of that, no aviation authority will certify a single engine transport airplane. Governments can't take the political risk of certifying a single engine transport that may crash due to engine failure. Passengers won't like it psychologically.
 
backfire
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 12:35 am

Rabenschlag,

Redundancy has everything to do with it.

It doesn't matter if you build the most reliable engine in history. What matters is that you have a backup for the day it goes wrong.

I haven't done the maths but the probability of a single-engine failure today might even be lower than that of a dual-engine failure on a older twin-jet (DC-9, 737-200, etc). Yet we've never used that reliability to justify eliminating redundancy.
 
Guest

RE: Why No Single Engine Jet?

Thu Aug 01, 2002 12:48 am

One of the main obstacles to a single-engined jetliner would be passenger confidence. No matter how reliable the engine is, many people would have a bad feeling in their gut about it. The reliability statistics wouldn't mean a thing to them.

For instance, if someone does business with a store or restaurant 20 times and gets treated shabbily only on the 20th visit, there's a good chance they won't go back for years. The statistical fact that they were a satisfied customer 95% of the time and a dissatisfied one only 5% of the time won't matter, or that the probability of it happening again might be fairly low. All they'll think about is that the place gives them a bad feeling in their gut.

Now imagine if one of these planes crashes due to engine problems. Even if it was an isolated accident and the engine boasts a 99.99999% reliability factor, the media will repeat over and over again that it was a one-engined plane with no backup in case that one and only engine failed. That would be enough to give millions of viewers that same bad gut feeling.
 
rabenschlag
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 1:07 am

Mcdougald,
i like your analysis. humans have big psychological troubles dealing with risks or dealing with very large and very small numbers in general. still, airbus luckily failed to persuade people that twins are something one should be afraid of. so they have a hard time to sell the four(money)holers. what if airlines could drastically cut costs with oneholers?

backfire,
i'm not completely convinced yet. in a way, redundancy is a way to reduce a certain risk. cutting risk is the end, an redundancy is ONE means to do so. we had no problem to sacrifice the redundancy of four engines to two engines as two have the same risk as four. or isnt it?

regards, r.





 
User avatar
ATA L1011
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 1:09 am

Yes with one engine if something goes wrong you dont havea backup, your up Sh**s creak!
Treat others as you expect to be treated!
 
SailorOrion
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 2:21 am

A critical system must not have a failure rate of more than 10e-9 / flight or flight hour. Jet engines are still lightyears away from this threshold, so there will be no single engine aircraft certified after Part 25 FARs / JARs in the foreseeable future.

SailorOrion
 
Ikarus
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 2:23 am

FAR/JAR 23 certified airplanes: High likelyhood within the next 20 years.

FAR/JAR 25 certified designs: NEVER.

It's as simple as that

Regards

Ikarus
 
cointyro
Posts: 62
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 2:31 am

Don't forget, there are loads of people flocking to Sir Richard's four-holers crossing the Atlantic instead of the passe 763 merely on the proven pyschological tendency for passengers to avoid any ETOPS situation, no matter how inconceivably unlikely. Crazy but true - and paying-passenger demand is what dictates what we fly just as largely as efficient operations.

People play the lotto don't they? Obviously people don't have a grasp on numbers outside the 0.01% to 100,000% range. Hence Branson's A340s and 744s jumping the pond on the shorter side of their endurance curves.

Regards,
Dan
 
srbmod
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 6:03 am

Airliners have had two engines minimum since the 1920s, when regs were put into place requiring airlines to fly a/c with at least two engines. This was in response to the TWA crash in which Notre Dame football coach Knute Rockne was killed. That aircraft was a single engine airliner, and after that crash, that type of a/c left commercial service (unless you count some of those Air Taxi services in AK that use Cessnas). When the jet age arose, the engines were not powerful enough to only use two engines, and add to this reliability issues with the early engines, and 4 engines made sense. Up until Airbus built the A300, the largest aircraft with two engines were the DC-9, the BAC 1-11, the Caravelle, and the 737. As technology has gotten better, newer designs allowed two engines because of the newer engine technologies made it safe and practical. Some aircraft have to have 3 or 4 engines just to get it off of the ground.
 
FDXmech
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 6:03 am

Don't forget, there are loads of people flocking to Sir Richard's four-holers crossing the Atlantic instead of the passe 763 merely on the proven pyschological tendency for passengers to avoid any ETOPS situation, no matter how inconceivably unlikely. Crazy but true - and paying-passenger demand is what dictates what we fly just as largely as efficient operations.

Well, you may be correct but I don't think so. The vast majority of pax don't know what type of aircraft they're sitting aboard, never mind how many engines are under the wing. They may be flocking to Virgin Atlantic but most likely for other reasons.


You're only as good as your last departure.
 
FDXmech
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 6:09 am

With so many proponents for twin-jets over quad-jets in this forum, shouldn't a single-jet be even better?

This logic could be reversed to read. With so many proponents of quads over twins, shouldn't we strive for five or more engines?

Let's separate fact from marketing hype when discussing the merits of twins or quads.

You're only as good as your last departure.
 
backfire
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 7:26 am

Take away the engines altogether and you'll eliminate the fundamental basis for engine failure  Insane
 
pmk
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 7:50 am

UH, Ikarus:

FAR/JAR 23 certified airplanes: High likelyhood within the next 20 years.

The Visionaire Vantage will be in the air next year. Single engine. FAR 23


Peter
 
delta-flyer
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 11:02 am

High reliability only means that there is a very low failure rate, but there is still a failure rate, nonetheless. That means that an engine will fail, only we don't know ahead of time when that will be.

There are two aspects to risk management -- one is to reduce the likelihood of occurrence of a bad event, and the second is to limit the severity of the event when (not if!) it occurs.

We accomplish the first by making things as reliable as possible. We accomplish the second by adding redundancies. Any chain of events that will lead to catastrophic event (a fire, loss of control, etc.) must not be greater than 1e-9, as someone noted above. So, we have to keep adding redundancies until all identifyable chains of events can be shown, at least on paper, to meet this safety requirement. This is why a passenger plane must have at least 2 engines.

All airframers have a department staffed by mathematicians and engineers called Reliability & Safety Engineering -- it's one of the most important disciplines in aircraft design. Their analysis ultimately dictates the architecture of the electrical, hydraulic, flight control, fuel and avionic systems, just to name a few. The high level of safety in aviation does not happen solely by keeping the planes maintained, but even moreso by the inherent design. As they say, "Safety is no accident."

Pete  Smile
"In God we trust, everyone else bring data"
 
gr8slvrflt
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 11:13 am

Airliners have had two engines minimum since the 1920s, when regs were put into place requiring airlines to fly a/c with at least two engines. This was in response to the TWA crash in which Notre Dame football coach Knute Rockne was killed. That aircraft was a single engine airliner, and after that crash, that type of a/c left commercial service (unless you count some of those Air Taxi services in AK that use Cessnas).

Knute Rockne was killed in the crash of a TWA Fokker F.VII trimotor. The cause of the crash was structural failure of the wooden wing due to internal rot. This crash spelled the end of wooden airliners in the US, not single-engine airliners. Lockheed and Northrop single engine planes were used for passengers until banned by the Civil Aeronautics Act of 1938. Before then, single engine aircraft offered superior speed than contemporary multi-engine types.
I work for Southwest, but the views expressed are my own and do not necessarily represent those of Southwest.
 
brianhames
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 11:23 am

Yeah, you'd need ESOPs
 
cloudy
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 2:30 pm

A few points -

1. It is my understanding that for airline operations a jet must be able to suffer an engine failure on takeoff and continue to climb, or at least not loose altitude. This is an obvious impossibility for a single

2. In general aviation, twins have a higher accident rate than equivalent singles. Twin engine airliners have a lower diversion rate than quads do. Redundancy increases safety but so does simplicity. There is a trade-off.

3. Airliners can glide a very long distance(can someone give us some figures?). Transport jets can land safely even if all engines were to fail at cruising altitude, provided a suitible landing surface is available. An Air Canada(I think) 767 ran out of fuel in the middle of nowhere and landed at an unused airport with no damage. Within the US and Europe, there is little if any risk to life from engine failure at altitude - airfields and highways abound.

Passengers and the media fear engine failure at high altitude.

Pilots fear engine failure durring takeoff or landing.

It is the later possibility that will probably prevent us from seeing single engine airliners.



 
gr8slvrflt
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 8:59 pm

What about a second engine for takeoff that would then be shut down and retracted or faired-over for cruise? This engine could also be brought into service if the main engine fails. Sort of like the hybrid gas/electric cars.
I work for Southwest, but the views expressed are my own and do not necessarily represent those of Southwest.
 
Guest

RE: Why No Single Engine Jet?

Thu Aug 01, 2002 9:38 pm

Cloudy made an interesting comment...

In general aviation, twins have a higher accident rate than equivalent singles. Twin engine airliners have a lower diversion rate than quads do. Redundancy increases safety but so does simplicity. There is a trade-off.

Cloudy's comment is correct, but don't make the assumption that the pilots involved in these light-twin accidents are fully qualified and proficient in their multi-engine aircraft. Unfortunately, VERY few light-twin pilots are. I know, I've given too many BFRs and ICCs to some of these people. They are usually very rusty and very dangerous. Believe me, it usually takes much longer than the basic 1 hour BFR to bring these guys up to speed. The sad part is many of these people have more money than sense and they simply don't fly enough to stay on top of things. Oh well, that's another topic... Bottom line is that it's this type of pilot that skews the statistics, not the well-trained, experienced professional (or amateur).

As far as "serious" flying in single-engine aircraft goes, there was a time when I wouldn't have given much thought to operating properly equipped and maintained single-engine (piston or turbine powered) aircraft almost anywhere, anytime day or night. That however, was a long time ago. Having "been around the block" several times now, I realize that there are just some operations that only a second engine can justify. I know that certain things can be done to enhance the redundency for single-engine IFR operations, like secondary vacuum pumps, generators, etc. and these ought to be considered mandatory; but none of these things will be sufficient when your trusty Continental, Lycoming, P&W PT-6, or whatever decides to pack it in for the evening.

As far as single-engine airliners, you can read about the last one that will ever be built in the history books. They were done away with in the 20's. (I'm not counting single-engine Part 135 IFR operations as airline operations.) In my humble opinion, I doubt if there will never be any single-engine aircraft much larger than the Cessna Caravan in the future - the potential legal liabilities are just too great. There is no way that Boeing is going to come out with a single-engine MD-11.
 
FDXmech
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 10:14 pm

Excellant post Delta-flyer.

The reasoning of four engines being good, three being better and two better yet so why not one defys logic and is readily apparent.

This is an example of reaching the point of diminishing returns.
You're only as good as your last departure.
 
L-188
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RE: Why No Single Engine Jet?

Thu Aug 01, 2002 10:24 pm

The problem isn't with the engines it is with the flight controls to the tail.

The problem is that the most logical place to put a turbine engine would be right out the tail. Just like the third engine on a 727, L-1011 or a Falcon.

The problem is in case of a uncontained engine failure. Because of where the engine is located there is a very good chance that failure mode will also take out the control runs to the tail surfaces and possibly the tail structure itself. Remember Sioux City and that DC-10.

Nobody has yet been able to figure out how to demonstrate how to design an aircraft of that type that eliminates that failure mode.

Anybody remember the Perigrain (Or whatever the name of that bird(falcon) is spelled) design from about twenty years ago. I can't remember who came up with it but it looked like an ASTRA with a single TFE731 that was mounted in the middle of the tail. It got cancelled during the recession that Carter started in the 1970's but it was an interesting design.

OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
rw774477
Posts: 1020
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RE: Why No Single Engine Jet?

Fri Aug 02, 2002 1:29 am

..... and in the unlikely event of an engine failure, we all die ... thank you for flying Air .....

rw774477
 
eugdog
Posts: 426
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RE: Why No Single Engine Jet?

Fri Aug 02, 2002 1:42 am

Aviation safety is determined by cost per life saved (currently $3 million per life)- this means that the cost of any saftey measure divided by lives it will save must be LESS then $3 million dollars.

ie cost of implementing fire suppression in cargo hold

Cost to industry (say) $200 million - potential lives saved (say) 50

therefore cost per life $4 million - hence safety measure is rejected!

There might come a time when engines become so reliable that the additional cost to industry of extra engines divided by lives saved exceeds $3 million.
 
FredT
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RE: Why No Single Engine Jet?

Fri Aug 02, 2002 2:18 am

When flying a single engine aircraft, you are to fly it in such a way that if an engine fails at any time in flight, you can handle it. That means always keeping an area suited for an emergency landing within gliding distance.

How many commercial operations would be willing to take the lack of flexibility this would give?

And yes, I know that many GA pilots do not fly this way. But they also end up killed when they stall their aircraft into forest areas while trying to fly way below best L/D speed to a landable area.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
delta-flyer
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RE: Why No Single Engine Jet?

Fri Aug 02, 2002 2:48 am

Redundancy increases safety but so does simplicity. There is a trade-off.
Excellent observation, Cloudy. This is what we, engineers, contend with all the time. But the SSA (System Safety Analysis) says the same thing in numbers -- adding redundant systems reduces overall a/c reliability, but is sometimes the only way that a particular failure scenario can be made to meet the 1e-9 probablity requirement.

FDXMech -- thanks for the compliment. There are many ways to accomplish the required safety -- how a particular airframer does it is based on their assessment of the economics of the market for which the a/c is designed. I suspect Airbus had a good reason for the four-engined A340, and similarly good reasons for the twin A330.

Aviation safety is determined by cost per life saved
Eugdog.... You make it sound as if planes are not sufficiently safe because of the cost of safety. That's not the case...they all meet the basic safety requirement that the probability of a catastrophic event is less than 1e-9. The economic factors you mention are used more to compare different solutions for reaching this standard, or for implementing improvements on designs that fall short. The bottom line is that nothing can be made 100% safe, with zero probability of failure. The goal of designers is to achieve the required level of safety at the lowest cost.

Pete
"In God we trust, everyone else bring data"
 
Klaus
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Cloudy

Fri Aug 02, 2002 3:26 am

Cloudy: Twin engine airliners have a lower diversion rate than quads do.

You´re making a popular mistake, here.

A quad has a slightly higher chance of at least one engine failing just because of the higher number of engines.

The point you´ve missed, however, is that a quad will still remain in a multiple-redundancy mode, while the twin is in a clear and direct emergency with no further safety margin. In addition, the twin will even have to operate its last remaining engine at a higher power level than the quad with its three remaining ones, which increases the probability of a failure of that last engine.


With an imagined engine failure rate of, say, 1%, the diverson rate for the twin would be about 2% (rounded), for the quad it would be about 4% (assuming the quad would even need to divert on a single-engine failure).

The all-engine-failure rates, however, would be 0.01% for the twin, but only 0.000001% for the quad. Quite significant.

The first set of numbers tells you how probably you´ll be inconvenienced, the latter is relevant for your survival. When in doubt, I know which one I would use for a decision.  Wink/being sarcastic


Cloudy: Redundancy increases safety but so does simplicity. There is a trade-off.

That would only be true if the additional systems depended on each other. Since practically all of them are working independently in parallel, however, there is no or only a very small gain in reliability to be achieved. Nothing comparable to the reduced redundancy. It´s basically a political decision to accept the increased risk.


Cloudy: 3. Airliners can glide a very long distance(can someone give us some figures?).

Not from an ETOPS 120 or 180 distance. Not by far.


Cloudy: Transport jets can land safely even if all engines were to fail at cruising altitude, provided a suitible landing surface is available. An Air Canada(I think) 767 ran out of fuel in the middle of nowhere and landed at an unused airport with no damage.

Incorrect.

They were over Canada, which hardly compares to the open Atlantic or the Pacific in terms of "middle of nowhere". And it was only due to a very improbable set of circumstances that they were able to land on an abandoned airstrip.

There was damage due to the inability to deploy the nose gear properly (in addition to a scraped engine pod, as far as I remember). If the plane´s tanks hadn´t been empty anyway (the reason for the emergency), there is the question if the higher weight would have made the landing a lot harder - and the fire that broke out after the landing a lot more dangerous.

The recent A330 gliding incident was also very close to disaster. It was pure luck they didn´t have to ditch because they happened to be close enough to the Azores.

Many people in here like to complain that the general public overestimates the risks involved in air travel. But naivity in the other direction is much more dangerous. Having been incredibly lucky for a few times doesn´t mean that there is no risk!


Cloudy: Within the US and Europe, there is little if any risk to life from engine failure at altitude - airfields and highways abound.

Just ask a few pilots whether they believe that bringing down a fully fueled airliner with all engines out on a traffic-heavy highway is their idea of an "acceptable risk".
 
airplay
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RE: Why No Single Engine Jet?

Fri Aug 02, 2002 3:27 am

FAR 25 901(c) states:

(c) For each powerplant and auxiliary power unit installation, it must be established that no single failure or malfunction or probable combination of failures will jeopardize the safe operation of the airplane except that the failure of structural elements need not be considered if the probability of such failure is extremely remote.

Never mind the all of the probability figures discussed, since 1977 this transport category aircraft standard has pretty much plainly said you need at least 2 powerplants and that's fine with me.

I think this type of redundancy is what is expected by the public from commercial civilian transport aircraft. Having said that I don't understand why single engine normal category (FAR 23) aircraft have been allowed to operate commercially in IFR conditions. I refuse to step on these single engine wonders. The question is not "if" the engine fails, its "when" the engine will fail.

 
SkyGuy11
Posts: 532
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RE: Why No Single Engine Jet?

Fri Aug 02, 2002 4:43 am

"Single engine jet? With passengers? Not for this pilot. Yes, they are reliable, but not 100% reliable. They quit every so often, like 2 days ago on the DAL 757 coming out of SNA. Ask those guys if they want to fly a single engine passenger jet. Flying single engine/single pilot while strapped to a Martin Baker ejection seat is acceptable risk for many thrill seekers. But a single engine passenger jet is just asking for death and destruction."

MD-88Captain, can you please elaborate on this or at least let me know where I can find out more about it? I fly out of SNA and am very curious about this, especially considering the rocket ship departure. You can email me if you like, buddy1997@earthlink.com. Thanks.
.
 
PPGMD
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RE: Why No Single Engine Jet?

Fri Aug 02, 2002 5:13 am

Not really going to get in this debate, but the Air Canada's 767 Glider, was calculated to have a 14:1 glide ratio. Thats about the same as a Cessna.
At worst, you screw up and die.
 
FDXmech
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RE: Why No Single Engine Jet?

Fri Aug 02, 2002 5:37 am

The point you´ve missed, however, is that a quad will still remain in a multiple-redundancy mode, while the twin is in a clear and direct emergency with no further safety margin. In addition, the twin will even have to operate its last remaining engine at a higher power level than the quad with its three remaining ones, which increases the probability of a failure of that last engine.

Can you point to a twin that suffered a dual engine failure other than failure caused by environmental factors (volcanic ash, flock of birds, etc) or fuel management related (exhausting fuel supply type scenarios).
As far as operating the engine at a higher thrust setting if one engine is shut down, what makes you think this setting would promulgate a second engine failure?

I think the operation of twin jets is well established and much doubt is being generated from airframe marketing departments.
You're only as good as your last departure.
 
Klaus
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FDXmech

Fri Aug 02, 2002 5:56 am

FDXmech: Can you point to a twin that suffered a dual engine failure other than failure caused by environmental factors (volcanic ash, flock of birds, etc) or fuel management related (exhausting fuel supply type scenarios).

No, I´m perfectly happy with the fact that this hasn´t happened - yet. The additional risk is pretty small, it appears, but it´s necessary to be aware of the fact that it still exists.


FDXmech: As far as operating the engine at a higher thrust setting if one engine is shut down, what makes you think this setting would promulgate a second engine failure?

Of course the engines are rated for this kind of occurrence; Again, it´s not a "cause" for the failure of the remaining engine. It´s merely an additional factor. Irrelevant in most situations; Possibly relevant when other negative factors come together. Nothing to get into panic about, just something to be aware of in a discussion like this.


FDXmech: I think the operation of twin jets is well established and much doubt is being generated from airframe marketing departments.

Both true. I still think that in this discussion, it would be wrong to completely ignore the additional risks that are involved in twin ops - and must be dealt with.

There seem to be quite a few cases of "overshoot" where people apparently seem to believe twins were somehow safer than quads. Of course entirely unrelated to certain marketing departments...  Wink/being sarcastic
 
T prop
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RE: Why No Single Engine Jet?

Fri Aug 02, 2002 6:56 am

Single engine pax jetliner? Not in our life time, see all of the reasons above.

Twins vs quads IMHO:

Trying to select flights on quads because one is concerned about the chance of both engines failing on a twin is ludicrous. You have a much higher chance of being struck by lightning, bitten by a shark or killed on the way to the airport.

The probability of both engines on a twin failing due to unrelated reasons is about as likely as having the wings folding up.

If I ever get to the point I'm worryed about this, lock me in a padded room.


T prop.
 
Klaus
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T Prop

Fri Aug 02, 2002 8:42 am

T prop: You have a much higher chance of being struck by lightning, bitten by a shark or killed on the way to the airport.

Might I remind you that most people do seem to be using lightning-conductors, get out of the water when a shark is in sight and try to drive cautiously to the airport?

Just a thought...  Wink/being sarcastic
 
FDXmech
Posts: 3219
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RE: Why No Single Engine Jet?

Fri Aug 02, 2002 8:58 am

Klaus
There seem to be quite a few cases of "overshoot" where people apparently seem to believe twins were somehow safer than quads. Of course entirely unrelated to certain marketing departments.

I agree.

I do find it ironic that, Airbus, who pioneered the widebody twin is now putting its money on several quads. Boeing, who picked up late on the widebody twin took the gauntlet and ran. Whereas Airbus rather than competing head to head on the same basic idea chose a retro niche, the traditional long distance four engine jet.

As much as I like the A340 family, I'm concerned that the A330 is languishing in the A340's shadow.
You're only as good as your last departure.
 
PPGMD
Posts: 2398
Joined: Sun Sep 30, 2001 5:39 am

RE: Why No Single Engine Jet?

Fri Aug 02, 2002 9:27 am

There is already an aircraft that can serve the A340's market. The funny thing is that it has been available for years.

The problem with Airbus is that they are competeing in markets that it has to get the people to buy them instead of Boeing. The Boeings have been around for years, its easy to get type ratings and many people have them, while with Airbus the pilots have to learn a new aircraft and a new way of flying.

I think that Airbus might succed with the A380, that is if Boeing doesn't just bring out a streched 747, which there are rumors that the Sonic Cruiser has been placed on the back burner so they can rework and make a bigger 747.
At worst, you screw up and die.
 
Klaus
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Joined: Wed Jul 11, 2001 7:41 am

FDXmech

Fri Aug 02, 2002 10:42 am

FDXmech: I do find it ironic that, Airbus, who pioneered the widebody twin is now putting its money on several quads.

Which seems quite consistent, since the A300 was never meant for long-range trans-oceanic service, as far as I know. And I guess an A380 with two hyper-monster engines would really be a bit too much for any technology we´ve got so far.  Wink/being sarcastic


FDXmech: Boeing, who picked up late on the widebody twin took the gauntlet and ran.

Basically betting the farm on none of their twins ever having a double inflight shutdown. The first such incident would probably yank the priorities back to redundancy over cost-saving. ETOPS tickets could become a hard sell, even at a discount.


FDXmech: Whereas Airbus rather than competing head to head on the same basic idea chose a retro niche, the traditional long distance four engine jet.

This discussion we´re having here would evaporate the second the news broke. People would remember basic math and there wouldn´t be anything "retro" about a quad, all of a sudden.

Quads aren´t invulnerable, either; Especially since independent inflight shutdowns aren´t the only (maybe not even the most prominent) possible problem. But there still is that extra safety margin. Which can only be ignored as long as it has never been needed. And so far, we´ve been lucky for a long time. With the expected increase of ETOPS-relevant movements, the odds aren´t exactly getting better.


FDXmech: As much as I like the A340 family, I'm concerned that the A330 is languishing in the A340's shadow.

I always thought the A340 was the "dog" there?  Wink/being sarcastic

Airbus is certainly right in there with the ETOPS crowd. They just leave the choice to the customers, up to a point. Boeing, on the other hand, with the 747 beginning to fade away seems to rely entirely on their continued luck. I just don´t know if that´s really such a brilliant idea in the long run...
 
T prop
Posts: 915
Joined: Tue Apr 03, 2001 4:33 pm

RE: Why No Single Engine Jet?

Fri Aug 02, 2002 11:48 am

Might I remind you that most people do seem to be using lightning-conductors, get out of the water when a shark is in sight and try to drive cautiously to the airport?

O.K. I thought about it.  Big grin

People still get zapped, bitten by sharks and crash thier cars, but no twin jetliner has had a double engine failure due to unrelated reasons.

And I thought about this.

Basically betting the farm on none of their twins ever having a double inflight shutdown. The first such incident would probably yank the priorities back to redundancy over cost-saving. ETOPS tickets could become a hard sell, even at a discount.

Although it has never happened, if it did unfortunately it would need to happen more than once and to different engine types to have this effect.

T prop.
 
FDXmech
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Joined: Sun Mar 19, 2000 9:48 pm

RE: Why No Single Engine Jet?

Fri Aug 02, 2002 12:21 pm

Klaus
Basically betting the farm on none of their twins ever having a double inflight shutdown. The first such incident would probably yank the priorities back to redundancy over cost-saving. ETOPS tickets could become a hard sell, even at a discount.

So in your mind, ETOPS, no matter how many decades of proven, safe and reliable service can never be fully accepted on the premise of an eventual double shutdown?

Would the same standards then be applied to an eventual fly by wire failure in which case we shall return to the redundancy of cable controlled flight controls?

You're only as good as your last departure.
 
cloudy
Posts: 1613
Joined: Sat Apr 06, 2002 3:23 pm

RE: Why No Single Engine Jet?

Fri Aug 02, 2002 3:40 pm

Klaus - I was not talking about ETOPS, I was talking about the possibility of engine failure at altitude. I never claimed you could glide to a safe landing over the Atlantic. I said "Within the US and Europe".

I also did not say that losing all engines even over safe territory would be something to look forward to. All I said it is much, much less of a risk than engine failure on takeoff. Engine failure on takeoff can and has killed people. Engine failure, alone and at altitude, hasn't been a problem in commercial jets - at least not for some time. When the 777 was designed - engine failure over the Atlantic was seen as a political/regulatory problem more than a real significant risk. A single engine failure on takeoff was the real problem Boeing had to deal with in the design, particularily the asymetrical thrust. Engine failure on takeoff is a showstopper, I think, for a single engine airliner.

What you and many other amateurs (I myself am an amateur) fail to do is to realize that everything is a trade off. It is true that there is a remote possibility of a double engine failure from unrelated causes. But there are far worse possibilities to worry about if I were you.

Uncontained engine failures DO happen with some regularity, people have died from them recently and in modern commercial jets. You increase your odds of having one if you have 4 as opposed to 2 engines. As I said before, redundancy provides safety but so does simplicity.
Boeing picked simplicity in this case
Quads FEEL safer, but twins arguably ARE safer.

Trade offs go even further - from what I heard, the FAA once declined to promulgate a new regulation because it would increase the cost of air travel so much that more people would drive instead. Since driving is more dangerous then flying on airlines, more people would die overall with the new regulation than without it.

Be carefull - the media likes to focus on small, overhyped risks. It is the overall risk you take by flying - or even by living in an industrialized society, that matters. And that is not as simple a matter as the Ralph Naders of the world would have you believe.

The A-330 emergency landing was caused by a fuel management problem, This problem could just as easily happened to a quad. no, it actually be more likely because fuel management in a Quad is usually a more complex task than in a twin
 
rabenschlag
Posts: 1012
Joined: Fri Oct 20, 2000 10:28 pm

RE: Why No Single Engine Jet?

Fri Aug 02, 2002 5:43 pm

puh, this has turned into a 2 vs. 4 discussion.

just let me try to summarise and add a new thought:

a) most of us reject single engine AC because we think an engine shut down will be lethal for sure.

b) we can never eliminate the risk that an engine will fail for internal reasons

c) we accept twins on long range over water, because there is always an airport within reach and several precautionary measures have to be installed in such AC

d) however, if the increase in risk associated with a technical change leads to dramatic monetary benefits, we (and the airlines) are willing to accept it. i think we all agree that there is a very slight increase in risk in two vs. four engine jets. but we find it neglible.


so: i think it needs few things before we will see single engine jets:


a) increase the gliding capacity of aircraft. , maybe this will be possible in the future without spoiling the aircrafts high speed capability.

b) put so many emergency airports along major routes that single engine aircrafts are always in gliding distance from one of them

c) automatize the reaction to the event of engine failure in that the aircraft always monitors the closest airport within gliding distance and the path to it.

d) anyhow put redundancy on the plane for take off


maybe some of these roblems seem hard to solve. on the other hand, the possible econimic profit may be very high. just a final example:

if you take flights within germany, i think condition b is almost met.

cheers, r.




 
Guest

RE: Why No Single Engine Jet?

Sat Aug 03, 2002 12:09 am

In some of the posts, only part 23 and 25 were mentioned regarding multi-engine requirements. I'd like to point out that the answer lies elsewhere. Part 121 (airliners operation) forbid the use of single engine airplanes (14 CFR 121.159- No certificate holder may operate a single-engine airplane under this part). I don't think part 135 has this provision but I'm not really sure. Part 23 and 25 do not prohibit single-engine airplanes.

Regards,
Nut

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