Tri vs Twin-jet

[Archer]

I've been trying ot find some single and twin engine performance for tri jets such as the 727 and the Falcons...

I was wondering if you guys could help me out.

Also, while we are on topic...what are some pros and cons compared to twin jets?

off the top of my head I can think of more redundance and better engine out performance for trijets...but also higher maintenance, cost and chance of engine failure.

 

[mar]

You really need an AFM

I can't help you with any of the performance questions but one obvious advantage to three or more engines is the freedom to operate without the constraint of considering ETOPS.

ETOPS stands for Extended Twin-engine...um...Operations...um...or is it Engines Turning Or Passengers Swimming?

I can't remember.

But the basic idea is that if an airplane is certified for 180 minutes ETOPS then that means it must always remain with 180 minutes of an enroute alternate in case of an engine failure.

Given the weather at some airports used for ETOPS alternates that might mean a longer leg than a three-engine or four-engine jet would've flown...

...so in that case was it more economical to operate a two-engine jet?

As somewhen once said: A 777 with an engine out over the middle of the Pacific is just a single engine plane out over the middle of the Pacific.

Lots of things to consider.

And when people ask me why I fly an airplane with four engines I tell them it's because they make very few with five engines.

 

[huncowboy]

Just curious. Any stories of 777s losing and engine over the oean yet? Sorrry for the hijack but wasn't going to open a thread for it.

 

[SkyWestCRJPilot]

In terms of efficiency it's more fuel efficicent to have one big huge turbofan engine than 4 small ones giving 1/4th the thrust of the big one. As engine reliability has improved aircraft designers have swithced to 2 engines as the basic design. The newest jet engines are so reliable that they hardly ever fail. Ironically the more engines you have actually increases the liklihood of an engine failure on your flight. If your engine has a failure rate of once every 10,000 hrs then with 2 engines at that same failure rate per engine you'll have an engine failure at once every 5000 hours with the two combined. With four, once every 2500 hours. Charles Lindbergh chose a single engine airplane to cross the Atlantic because he knew this exact same logic. But with 3 or 4 engines you don't have to worry about ETOPS restrictions. That's why 747 and A340s are popular for real long haul flying and that's probably one reason why the A380 will have 4 engines instead of 2. Conversely the efficiency created by 2 engines is why the 7E7 will only have 2. GE is hoping to extend ETOPS on the 777 engines to 330 min from 180 min. Here's the article. Link

 

[mar]

Any stories of 777s losing and engine over the oean yet?

USA Today article "Finding a safe place to land."

Monday, December 4, 2000

By Alan Levin
USA TODAY

SHEMYA ISLAND, Alaska -- If this tiny speck of tundra is known at all, it is for fierce winds and top-secret intelligence work. Virtually unseen is the vital role it plays in aviation safety.

An airport here and a constellation of equally remote airstrips have for decades served as last-ditch havens for fliers traversing the northernmost regions of the globe.

But as the number of lengthy flights over these areas soars and airlines clamber to open routes over the North Pole to shave valuable time off flights from North America to Asia, the long-neglected rules governing these airports and the flights above them are under fire.

Some pilots and aviation experts contend that airports like the one on Shemya are not prepared to handle a major emergency. Indeed, severely injured passengers on a Chinese jet that made an emergency landing on Shemya in 1993 lay on stretchers for hours before being transferred to mainland hospitals. At least two people died in the incident.

And, the critics say, rules governing such things as how much fire
protection and medical equipment are needed on the jets that ply these routes are out of date and inadequate. ''You have very few options on the polar route,'' says Joan Sullivan Garrett, whose company MedAire Inc. links flight crews with doctors to handle in-flight emergencies.

A related issue already has sent bitter shock waves through the aviation world. In January, after an angry debate, the Federal Aviation Administration granted carriers more flexibility when flying two-engine jets over the north Pacific. The fight pitted European regulators against the FAA, Airbus Industrie against Boeing, its rival in the production of large jets, and some pilot groups against their employers.

No one is saying the long flights over the world's most desolate regions pose a dire risk. But, just like the island of Shemya, officials say this obscure issue is of huge significance to the future of long-range flights.

Aviation powerhouses like the FAA and Boeing agree. Though both point to the excellent safety record of these flights, they have endorsed a re-examination of the rules. Earlier this year, the FAA assembled dozens of industry experts on a panel to recommend improvements.

When visibility is zero

At 300 feet above Shemya's runway, visibility is zero. The Boeing 727 supply jet rumbles in amid the hiss of compressed air in the cockpit and the whine of jet engines outside. But the milky white veil covering the windshield creates an impression that the jet has stopped.

Capt. Jon Bergstedt, a pilot for Reeve Aleutian Airways, routinely flies in conditions like these. In summer months, low-level clouds and rain blanket the island. In winter, unpredictable, heavy winds whip the treeless landscape.

Delivering a load of passengers and cargo to this intelligence-gathering outpost, Bergstedt has descended as low as the rules allow in bad weather and is heading toward a radio beacon at the end of the runway. Before he can land, though, he or crewmembers Steve Wooliver and Trig Bjorklund need to
catch sight of the runway. With only enough fuel for one pass, it doesn't look good.

Co-pilot Wolliver opens his mouth to announce an aborted approach but before he can speak, Bjorklund barks, ''Landing lights.'' A pier holding a string of lights pops out of the mist to the left.

In rapid-fire maneuvers, the pilot turns toward the runway, then banks back to the right to line up with the rapidly approaching 10,000-foot strip of concrete. The runway is visible now, but with each turn it appears to rock wildly back and forth in the windscreen. Within seconds, Bergstedt straightens out, and the jet kisses the pavement.

''That would be something coming in there in a 777 with one engine,'' Wolliver says a few moments later.

Within range of a runway

That is just what the twin-engine Boeing 777, perhaps the world's
most-advanced jet, is designed to do. And if an engine failure or other problem occurred midway between North America and Asia, Shemya is one of the emergency strips pilots would head toward.

An engine failure on a 777 is extremely unlikely. But it does happen -- 10 times in the 117,800 long-range flights from June 1995 though last March. An engine on American Airlines Flight 129 from San Jose, Calif., to Tokyo stopped shortly after takeoff on April 4, forcing an emergency landing in San Francisco.

Under FAA rules, airlines that cross the Pacific with two-engine jets have to take a route that stays within about 1,500 miles of the nearest approved ''diversion'' airport so that the aircraft would fly no more than three hours on a single engine. If an engine died over the ocean, the pilot would fly toward the closest approved airport -- north toward Alaska, south to Midway Island, northwest toward Russia or west toward Japan.

On Shemya, pilots landing in an emergency would find a long runway and special aircraft firefighting equipment, but not much more. A few aging aircraft hangers line the airport, which normally shuts down at 5 p.m. Flights to Anchorage, the nearest large city, take at least five hours. Because of rapid changes in weather, the Air Force warns visitors that they could easily be stranded here for days.

Flying this route with a jet like the 777 would have been unthinkable just 15 years ago. The foundation of safe flight holds that any critical system -- with engines at the top of that list -- needs a backup. For most of the jet age, flying on one engine alone was to be avoided at all costs.

But modern engines have become hundreds of times more reliable than the jets introduced in the 1960s. A 777 engine fails about five times during every 1 million hours of flight, and most of those failures occur right after takeoff. The chances two engines would sputter to a stop in a 3-hour span are extremely remote. Such a failure has never caused an accident.

Just to make sure, the FAA mandates numerous safety measures on two-engine jets that fly across the oceans or other rugged terrain.

In January, the FAA finalized rules that allow even longer diversions on two-engine jets. Over the north Pacific, specially equipped 777s can now fly routes that are nearly 3½ hours from an airport, or about 1,700 miles.

Boeing and three airlines -- United Airlines, American Airlines and
Continental Airlines -- wanted the change to give them the flexibility to keep flying their regular routes when bad weather socked in diversion airports three hours away. The Air Line Pilots Association, which represents pilots for United and other carriers, supported the plan. So far, only a handful of such flights have been flown.

The proposal drew vehement objections from Airbus -- which sells the A340, a four-engine competitor to Boeing's 777 that is capable of similar flights -- as well as American Airline pilots and European regulators. They said that the change posed an unacceptable additional risk and argued that, because
the FAA did not take into account wind, the maximum diversion could be even longer than the new policy envisioned.

An analysis by a consortium of European aviation firms found that a 207-minute flight on one engine, the maximum length permitted by the new FAA policy, posed an unacceptable risk. The extended flights would set back safety enhancements 15 years, the group said.

''An accident will become a real possibility,'' Yves Roncin, an expert with the European Association of Aerospace Industries, wrote in a letter to the FAA last year.

Airbus, which also sells twin-engine jets, has so far not applied to extend the length of flights that its jets can take over water.

<<Continued>>

 

[mar]

<<Continued>>

The rules for older jets

Boeing, the airlines and the FAA insist that the flights are safe. Most independent aviation safety experts agree. ''I think that the real risk at 180 minutes isn't significantly different from 207 minutes,'' says John Hansman, director of the Massachusetts Institute of Technology's International Center for Air Transportation.

However, when the dust settled in this heated debate, all the parties agreed on one point -- while the world argued the fine points of safety on two-engine jets, similar issues on three- and four-engine models that routinely fly over the same areas fell by the wayside. In some cases, the rules governing their operation haven't changed in 45 years.

For example, diversions on the four-engine 747, though rare, occur more than twice as often as on the 777, according to statistics from Boeing. A similar pattern exists on Airbus' two- and four-engine jets. Yet an airline can fly a 747 over the North Pole or across the North Pacific without checking to see that airports along the route are clear of bad weather.

For two-engine jets to fly across remote areas, an airline must not only ensure that there is good weather at diversion airports, but must also certify that the airport has specially equipped firefighting teams. Three- and four-engine models have no such requirement.

A cargo fire is just as likely to strike an MD-11, a 747 or an A340, all of which have three or four engines, as a 777. Yet the rules governing 777 flights -- and other two-engine jets over water -- call for cargo bin fire extinguishers that last for more than 3 ½ hours. The other jets need only carry cargo fire extinguishers lasting 30 minutes. (Major U.S. carriers flying long-distance routes with three- and four-engine jets all have more fire protection than the law requires, but none have as much as the 777.)

Northern facilities 'pathetic'

There are other reasons, according to some of the world's top safety experts, that all jets flying long routes should be treated similarly.

The protections on two-engine jets flying remote routes are designed mainly in case of a mechanical failure. But about half of all diversions occur even though nothing is wrong with the jet, according to Boeing.

Many are for medical emergencies. An FAA analysis of medical problems requiring diversions found that they are several times more likely to occur on a jet carrying 300 people than an engine problem. Theoretically, the risk would increase on the double-decker A3XX and the extended 747X, the jets being developed by Airbus and Boeing to carry as many as 600 people.

Garrett, whose company advises airlines on medical issues, says she has studied the medical facilities available near airports in northern Russia, Alaska and the Arctic Circle. They are ''pretty pathetic,'' she says.
Generally, if a passenger became ill on a polar flight, her company,
MedAire, would advise a flight crew to continue to a modern city like Anchorage rather than fly to the nearest airport.

As jets get larger and routes more remote, Garrett believes the airlines and aviation regulators around the world need to start thinking about requiring more complete medical facilities on board jets, possibly even a doctor. ''If there is nothing on the ground, there is no point in landing that plane,'' Garrett says.

For all these reasons, the FAA earlier this year convened an advisory committee of industry officials, pilots, consumers and government officials to study safety issues of long-range flights and draft proposed new rules. ''It's just clearly the right thing to do,'' says Thomas McSweeny, the FAA's chief of regulation and certification.

In addition to examining safety on the jets that ply these icy routes, the advisory board will examine what steps need to be taken to ensure that airports like Shemya or Petropavlovsk-Kamchatsky in northeast Russia are adequate to meet the growing need for safe places to land.

Capt. Chester Ekstrand, a Boeing official who is the firm's point man on long-range flight, says the company has been ''pleasantly surprised'' at the quality of the remote airports it has surveyed. ''That doesn't mean we don't have challenges,'' Ekstrand says.

At Petropavlovsk-Kamchatsky, which officials describe as one of the most modern Russian diversion airports, weather reporting is not always reliable, for example. At least one diversion airport is used so rarely that Boeing must financially subsidize it.

Weather, particularly in winter, plagues these northern airstrips. At Shemya, the winds are so fierce that Pentagon planners say construction workers can only perform some tasks during one month of the year, July. (The island is a proposed site for radar that would be used in the U.S.' long-range missile defense system.)

Pilot groups, even those that support increased flexibility for long-range flights, say they worry that an emergency evacuation in a wintry Siberian climate with sub-zero temperatures could cause as many fatalities as a crash. Others worry that some airports could close, reducing a pilot's options.

''We'd like to see that there's a building nearby so passengers can stay warm, that there are medical facilities somewhere nearby,'' says Capt. Michael Cronin, the American pilot and legislative director for the Coalition of Airline Pilots Associations. ''There is a firefighting requirement, but it is very modest. We'd like to see that enhanced.''

A major emergency

The number of jets that develop problems on long flights is extremely low. But on April 6, 1993, a China Eastern Airlines flight from Shanghai to Los Angeles demonstrated what might happen in the event of a major emergency over the Pacific.

The MD-11, carrying 235 passengers and 20 crew, began oscillating wildly at 33,000 feet after a pilot accidentally moved a panel on the wing. The motion tossed passengers around the cabin like dolls. Air traffic controllers told the pilots to fly north 950 miles to the nearest airport, Shemya.

Two hours after the incident, the jet touched down on Shemya's windy, snowy runway, according to an official Air Force account. ''The interior structure of the aircraft was significantly damaged. There was food, blood, vomit and bodies throughout the rear and central cabin. The stench was that of a 'slaughter house,' '' according to an account of the incident by historians
at Elmendorf Air Force Base.

The evacuation was slowed because the airport had only one stair that could reach the aircraft exits, the Air Force said. The medical facility had supplies to treat 30 patients, one-fifth of the 156 victims.

Luckily, though, Shemya was an Air Force base at the time with a doctor on its small staff. The injured were taken to a hanger and within hours the most serious were placed on planes and flown to Elmendorf, near Anchorage. About 10 hours passed from the incident until the first passengers arrived at hospitals on the mainland.

Two passengers died from their injuries. A flight attendant was declared brain dead a short time later.

Doctors who treated the injured that day said the delays in treatment probably did not cause any deaths, but the arrival of so many casualties severely taxed even the large hospitals of Anchorage.

''It was an extremely busy day,'' recalls Steven Floerchinger, a surgeon who treated the victims at Providence Hospital.

Regulators know airports like Shemya are far from perfect, but they say that's not their purpose. They are a final stopgap in the event of some major problem like an onboard fire or a mechanical breakdown, says the FAA's McSweeny.

Still, with two new jet models capable of flying as far as 10,000 miles, farther than ever before, due on the market within two years and airlines poised to turn demonstration flights over the North Pole into daily routes, McSweeny and others say the standards need to be reviewed.

''The international community needs to get on with assuring the availability of adequate alternate airports for all airplanes,'' says Boeing's Ekstrand.

 

[labbats]

With more than two engines, your takeoff minimums become less too I believe.

 

[Citationkid]

single engine performance for tri jets such as the the Falcons...

I was told 700 fpm on one engine for the Falcon (not sure if it was the 50 or 900).

 

[Capt. Caucasian]

With more than two engines, your takeoff minimums become less too I believe.

Our take-off mins for the E145 (two engines) is 600, 600, and 600 RVR. That is abou tas low as you can get. The reason is because we are part 121 were the rules are different than 91.

 

[kevdog]

3 holin is more fun than 2.

 

[nosewheel]

4 holin is more fun than three

 

[DAS at 10/250]

The newest jet engines are so reliable

What new jet engines?

Are you talking about the "new" turboprops they are calling high bypass turbofans?

I haven't seen a jet engine in a while outside of the 73/727's.

 

[Archer]

So I guess the question comes down to which is more likely, a twin engine failure on a tri-jet or a single engine failure on a twin-jet.

I doubt one jet engine is more reliable than other by significant amounts...the engine of a Falcon 900 and a Falcon 2000...I'm sure they are both pretty much of the same reliablity.

So that would mean tri-jets are that much less likely to have to fly with only one engine left...

taking it further...if 2 engines on a twin-jet is very unlikely, a triple failure on a tri-jet must be near impossible...

plus I think it would be less of an yaw moment on a tri-jet engine failure than a twin-jet...especially if the centerline one fails...which creates no yaw at all

 

[ThomasMore]

More engines is gooder...

The more engines you got, the better.

Six is a good starting point...

(B-47, An-225)

Eight probably gives you a better chance, though...

(Spruce Goose, B-52)

You're pretty safe with ten engines...

(B-36: 6 recips + 4 jets, Soviet "Caspian Sea Monster" ekranoplan: Wing-In-Ground effect transport -- 8 jets on the nose, 2 more on the tail)

But for me, personally, I'll take twelve.

(Dornier Do-X)

'sides. The more engines ya got, the faster ya go, right?

 

[bigsky]

There is definitely an added sense of security with a 3 or 4 engine jet. The numbers are small but problems do arise. I think I can remember about 3 or 4 777s that have had to divert due to inflight shut downs just this year. ( I believe continental landed in Midway, somebody diverted to Shannon, ect...)
I have never had an engine failure but once we were losing oil pressure so decided to operate the engine at flight idle- we were in a dc-10 and were able to maintain our altitude and speed as we were on the NAT tracks. When you have such a problem being in a 3 or 4 engine aircraft makes the 3 hour flight to land a little less stressful.

 

[DAS at 10/250]

I do remember a Discovery Wings program on the 777 and they stated that the dispatch reliability of the 777 was better than the 747. Their comment was that there was twice as much to go wrong on the 74.

 

[BoilerUP]

In the simulator, the B727-100 gets about 400-700fpm during a two-engine missed approach until you get cleaned up. You do NOT execute a missed single-engine, so I wouldn't know. The sim struggles to make 250 clean at max EPR on a single engine, and if you get low and/or slowed you are out of luck.

Just took my sim check yesterday, so these are my experiences, your mileage may vary...hope this helps!

 

[CesnaCaptn]

I hate to start a post with, "I was on the jumpseat and the captain said," but I was on the jumpseat of a 777 and the captain said there was a UAL 777 flying Aukland to LAX that lost an engine. He said it was the longest single engine 777 op, at over 3 hours. They ended up at HNL.

One more more thing. When Charles lindbergh was asked why he didn't fly a twin across the pond, he responded with, twins are twice as likely to have an engine failure.

 

[Archer]

You do NOT execute a missed single-engine

Out of curiosity, what WOULD you do? I would assume flying on one engine is better than flying with none...if you an sustain level flight at all that is...

About the transaltantic crossing in piston GA aircraft...a guy who crossed in a Turbo Arrow III said the same thing...a twin is more likely to loose an engine, and the remaining engine will just make control harder.

I must disagree. Even the worst light twin can sustain flight at a couple thousand feet. North atlantic is cold usually...so temperature is not an issue...and you are flying at a couple thousand feet.

I personally would feel more comfortable knowing that if one engine failed...even if it's more likely to fail, I have another one that will keep me fro having to swim in freezing waters with no land within hundreds of miles...

A twin engine failure in a twin is definitely lower chance than a single engine failure in a single.

One thing I'll be looking into is 747 single engine performance...

yeah having 4 engines seems good an all...but what if you loose 3 engines? no point is having that fourth one...it cannot probably maintain level flight and the adverse yaw must be insanely huge if the outboard one is all you have.

But I guess it comes down to the chance of a single engine failure on a twin vs. a 3 engine failure on a 4-engine plane...which is less

I'm very surprised at all these 777 Engine failures...in my class I was shown a video that said today's turbojet engines are so reliable that most pilots won't experience one in their entire careers...

 

[A Squared]

One more more thing. When Charles lindbergh was asked why he didn't fly a twin across the pond, he responded with, twins are twice as likely to have an engine failure.

Yes, but this has to be taken in the proper context. It is likely that the twin engine airplanes available in 1927 were not capable of continuing the flight on one engine. So, single engine airplane, lose an engine, go for a swim, twin engine airplane, lose an engine, go for a swim, but the twin is twice as likely to lose an engine, so you're twice as likely to swim.

Many of toay's light twins could keep on trucking with one engine shut down, (depending on how heavy it was when hte engine failed) so a twin is still twice as likely to have an engine failure, but, the chances of swiming are much less, not more, as in Lindbergh's day.