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Twinjet

Twinjet

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A twinjet or twin jet is a jet aircraft
Jet aircraft
A jet aircraft is an aircraft propelled by jet engines. Jet aircraft generally fly much faster than propeller-powered aircraft and at higher altitudes – as high as . At these altitudes, jet engines achieve maximum efficiency over long distances. The engines in propeller-powered aircraft...

 powered by two engine
Jet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...

s. Such configuration of an aircraft is the most popular today for commercial airliners, for fighters
Fighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...

, and many other kinds, because while offering safety from a single engine failure, it is also acceptably fuel-efficient.

Aircraft configurations


As of today, there are three most common configurations of this kind of an airplane. One has an engine mounted beneath each wing, and another has one engine mounted on each side the rear fuselage, close to its empennage
Empennage
The empennage , also known as the tail or tail assembly, of most aircraft gives stability to the aircraft, in a similar way to the feathers on an arrow...

. In the third configuration, both jet engines are within the fuselage, side-by-side. The third configuration is notable for being used on most fighters since 1960s, and still continuing, for example in the Su-27
Sukhoi Su-27
The Sukhoi Su-27 is a twin-engine supermanoeuverable fighter aircraft designed by Sukhoi. It was intended as a direct competitor for the large United States fourth generation fighters, with range, heavy armament, sophisticated avionics and high manoeuvrability...

 'Flanker', the F-15 Eagle, or the F-22 Raptor.

Failure safety


When flying far from diversionary airports, (so called ETOPS/LROPS
ETOPS/LROPS
ETOPS is an acronym for extended operations as re-defined by the US Federal Aviation Administration in 2007 . This rule allows twin-engined airliners to fly long-distance routes that were previously off-limits to twin-engined aircraft...

 flights), the aircraft must be able to reach an alternate on the remaining engine within a specified time in case of one engine failure. Power is not an issue. One of the engines is more than powerful enough to keep the aircraft aloft. Mostly, it is about maintenance and design requirements ensuring that a failure of one engine cannot make the other one fail, also. The engines and related systems need to be independent and (in essence) independently maintained. ETOPS/LROPS
ETOPS/LROPS
ETOPS is an acronym for extended operations as re-defined by the US Federal Aviation Administration in 2007 . This rule allows twin-engined airliners to fly long-distance routes that were previously off-limits to twin-engined aircraft...

 is often incorrectly thought to apply only to long overwater flights. In fact it applies to any flight more than specified distances from an available diversion airport. Overwater flights near diversion airports need not be ETOPS/LROPS
ETOPS/LROPS
ETOPS is an acronym for extended operations as re-defined by the US Federal Aviation Administration in 2007 . This rule allows twin-engined airliners to fly long-distance routes that were previously off-limits to twin-engined aircraft...

 compliant.

In the event of an engine failure, the remaining engine must provide enough thrust to keep the airplane in flight even if the failure occurs during take-off at a point where it is too late to reject the take-off. In other words a fully laden twinjet must be able to climb on one engine.

Due to the lack of engine redundancy
Redundancy (engineering)
In engineering, redundancy is the duplication of critical components or functions of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe....

, in the event of volcanic ash ingestion as happened with the air travel disruption after the 2010 Eyjafjallajökull eruption
Air travel disruption after the 2010 Eyjafjallajökull eruption
In response to concerns that volcanic ash ejected during the 2010 eruptions of Eyjafjallajökull in Iceland would damage aircraft engines, the controlled airspace of many European countries was closed to instrument flight rules traffic, resulting in the largest air-traffic shut-down since World War II...

, airline operators of twinjets must be equally as cautious and safety
Safety
Safety is the state of being "safe" , the condition of being protected against physical, social, spiritual, financial, political, emotional, occupational, psychological, educational or other types or consequences of failure, damage, error, accidents, harm or any other event which could be...

 conscious as operators of aircraft with three
Trijet
A Trijet is an aircraft powered by three jet engines. Early twin-jet designs were limited by the FAA's "60-minute rule", whereby the flight path of twin-engined jetliners was restricted to within 60 minutes' flying time from a suitable airport, in case of engine failure. In 1964 this rule was...

 or more engines in any areas affected by aerial ash fallout
Fallout
Fallout or nuclear fallout is the residual radiation hazard from a nuclear explosion.Fallout may also refer to:*Fallout , a 1997 post-apocalyptic computer role-playing game released by Interplay Entertainment...

. Thus far in the course of modern aviation history
Aviation history
The history of aviation has extended over more than two thousand years from the earliest attempts in kites and gliders to powered heavier-than-air, supersonic and hypersonic flight.The first form of man-made flying objects were kites...

, two four-engined passenger aircraft; a British Airways Flight 9
British Airways Flight 9
British Airways Flight 9, sometimes referred to by its callsign Speedbird 9 or Jakarta incident, was a scheduled British Airways flight from London Heathrow to Auckland, with stops in Bombay, Madras, Kuala Lumpur, Perth, and Melbourne....

 in 1982 and a KLM Flight 867
KLM Flight 867
On 15 December 1989, KLM Flight 867 en route to Narita International Airport, Tokyo from Amsterdam was descending into Anchorage International Airport, Alaska when all four engines failed...

 in 1989, suffered engine failures due to volcanic dust ingestion.

Efficiency


Twin jets tend to be more fuel-efficient than aircraft with three or more engines. Fuel efficiency in airliners is a high priority, and a high percentage of airliners use two engines. The Boeing 737
Boeing 737
The Boeing 737 is a short- to medium-range, twin-engine narrow-body jet airliner. Originally developed as a shorter, lower-cost twin-engine airliner derived from Boeing's 707 and 727, the 737 has developed into a family of nine passenger models with a capacity of 85 to 215 passengers...

 twinjet stands out as the most produced jet airliner. Other Boeing twin jets include the Boeing 767
Boeing 767
The Boeing 767 is a mid-size, wide-body twin-engine jet airliner built by Boeing Commercial Airplanes. It was the manufacturer's first wide-body twinjet and its first airliner with a two-crew glass cockpit. The aircraft features two turbofan engines, a supercritical wing, and a conventional tail...

, 777
Boeing 777
The Boeing 777 is a long-range, wide-body twin-engine jet airliner manufactured by Boeing Commercial Airplanes. It is the world's largest twinjet and is commonly referred to as the "Triple Seven". The aircraft has seating for over 300 passengers and has a range from , depending on model...

 (currently the world's largest twin jet airliner), and 787
Boeing 787
The Boeing 787 Dreamliner is a long-range, mid-size wide-body, twin-engine jet airliner developed by Boeing Commercial Airplanes. It seats 210 to 290 passengers, depending on the variant. Boeing states that it is the company's most fuel-efficient airliner and the world's first major airliner to use...

. Competitor Airbus produces the Airbus A320
Airbus A320 family
The Airbus A320 family is a family of short- to medium-range, narrow-body, commercial passenger jet airliners manufactured by Airbus Industrie.Airbus was originally a consortium of European aerospace companies, and is now fully owned by EADS. Airbus's name has been Airbus SAS since 2001...

 and A330
Airbus A330
The Airbus A330 is a wide-body twin-engine jet airliner made by Airbus, a division of EADS. Versions of the A330 have a range of and can accommodate up to 335 passengers in a two-class layout or carry of cargo....

, and the upcoming A350
Airbus A350
The Airbus A350 is a family of long-range, wide-body jet airliners under development by European aircraft manufacturer Airbus.A consortium originally comprising European aerospace companies from the UK, France, Spain and West Germany, Airbus is now fully owned by EADS and since 2001 has been known...

.

Many airlines use twin jets exclusively nowadays, such as American Airlines
American Airlines
American Airlines, Inc. is the world's fourth-largest airline in passenger miles transported and operating revenues. American Airlines is a subsidiary of the AMR Corporation and is headquartered in Fort Worth, Texas adjacent to its largest hub at Dallas/Fort Worth International Airport...

, Continental Airlines
Continental Airlines
Continental Airlines was a major American airline now merged with United Airlines. On May 3, 2010, Continental Airlines, Inc. and UAL, Inc. announced a merger via a stock swap, and on October 1, 2010, the merger closed and UAL changed its name to United Continental Holdings, Inc...

, and US Airways
US Airways
US Airways, Inc. is a major airline based in the U.S. city of Tempe, Arizona. The airline is an operating unit of US Airways Group and is the sixth largest airline by traffic and eighth largest by market value in the country....

 in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

.

Introduction to transoceanic flights


Since the 1990s airlines have increasingly turned from four-engined to twin-engined airliners to operate transatlantic and transpacific routes. On a nonstop flight from America to Asia the long-range aircraft usually follows the great circle route
Great circle
A great circle, also known as a Riemannian circle, of a sphere is the intersection of the sphere and a plane which passes through the center point of the sphere, as opposed to a general circle of a sphere where the plane is not required to pass through the center...

. Hence, in case of an engine failure in a twinjet (like Boeing 777
Boeing 777
The Boeing 777 is a long-range, wide-body twin-engine jet airliner manufactured by Boeing Commercial Airplanes. It is the world's largest twinjet and is commonly referred to as the "Triple Seven". The aircraft has seating for over 300 passengers and has a range from , depending on model...

), it is never too far from an emergency landing fields in western Canada, Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

, or eastern Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

. The Boeing 777 has also been approved by the Federal Aviation Administration
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...

 for flights between North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 and Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

, which is the world's longest regular airline route with no emergency landing fields along the way.