Introduction

Presently, with the fuel prices rising, and increased competition from other modes of transportation, Airline companies are trying every which way to reduce the operational costs and increase revenue. Out of which something that takes up a considerable amount of their expenses is the fuel costs. A lot of factors are responsible for the amount of fuel consumed by aircrafts. This includes the size and configuration of the aircraft, the age and efficiency of the engines, the number of people its carrying, the structure of the aircraft, and environmental factors like wind speed and ambient temperature.

While many of these things are beyond airline’s control, there are some things airline companies can do to make major improvements in the fuel consumption and save millions of dollars in annual fuel costs. This includes

• Buying new aircraft
• Improving technology onboard the aircraft
• Improving the way the aircraft is operated. This involves,

a) Flying more efficient routes: With the right information, pilots can fly shortest routes, take advantage of external factors and takeoff and landing trajectories that save fuel.

b) Know the airport: Every airport is different. Airlines can reduce fuel burn by understanding and adopting best practices for flying into and out of airports, flying holding patterns and taxiing between the runway and the terminal.

c) Adjust to changes: With access to the most current data like real time weather updates, pilots can adopt course and altitude changes to minimize the impact of winds, turbulence and other natural conditions that might lead to the usage of more fuel.

We will be discussing the technological improvements and some basic operational strategies that are made mandatory by several aircraft companies at the moment.

Cutting down weight in the cabin to save fuel

In 1987 American Airlines removed a single olive from each of its in-flight salads, Robert Crandall, then head of the airline noticed that the olives are left uneaten by the 75 percentage of their guests. This lead to reduction of an ounce in weight per food tray, saving the total costs by a remarkable $US40, 000 ($55, 000) a year.

Airline companies have been in the process of reducing the weight carried in their aircrafts for decades, From lightweight aluminum seat frame to the number of serving trays used in the cabin, airline companies have tried it all and is still in the process of reducing what they carry.

United Airlines made headlines in the newspapers recently with their decision to go for light weight papers in their In-Flight Magazines. I mean how lighter can a Paper get? As Per united, they were able to save an ounce from each magazine cutting down costs.

The United operates 744 mainline planes of different models, carrying about 50 to 366 passengers each. For a normal 737 plane carrying 180 passengers, the reduction will lead to about 11 pounds per flight. The airline said that this method of weight reduction is saving 170, 000 gallons of fuel a year, or $290, 000 in annual fuel costs.

United has also stopped on board sales of duty-free items like perfumes, chocolates and liquor cutting 1. 4 million gallons of fuel a year at a cost savings of $2. 3 million.

Virgin Atlantic recently announced a modified tray design that can accommodate more tray when stacked. Almost 33% more trays per cart can be accommodated which lead to Virgin Atlantic getting rid of one tray cart each flight, saving them around 53 lbs each flight. They have announced that that losing a pound in weight from every plane in its fleet will save 53, 000 litres of fuel a year, adding up to thousands of dollars.

Lufthansa also made news with their move to reduce the weight by replacing their existing containers with a light Weight one that weighs 31 lbs less. That’s 15. 4 million pounds in weight considering the size of their fleet, which is expected to save the airline 2, 000 tons of fuel every year. In 2011, United Airlines purchased 11, 000 iPads to replace pilots’ bulky paper manuals and replaced it with them saving a 326, 000 gallons of fuel annually. Recently, the U. S. Air Force joined the trend and replaced their onboard flight bags with 18, 000 Tablets, saving about $50 million USD a year. Now, American Airlines has replaced their Kitbags with iPads, which will save thousands of gallons of fuel considering they have over 14, 000 daily flights.

Operational practices: Single Engine Taxiing

The taxi-out time is defined as the time that the aircraft spends on the airport before it takes off. The aircraft here is waiting on the surface with its engines running, and this also includes the time spent on the taxiway system and in the runway queues.

Aircraft taxiing contribute a great extent to the fuel burn and emissions at airports. With giant engines chugging out gallons of fuel every second. The amount of fuel consumed depends on the taxi times of each aircraft, other factors such as the throttle settings of the engines, number of engines that are powered, and the control room decisions regarding engine shutdowns during delays. Fuel burn and emissions can be reduced to almost half if all aircraft were to taxi out using only a minimum number of their engines whenever possible. This means using one engine for twin-engine aircraft, This method is called as single-engine taxiing.

Every engines must be warmed up before taking off, for a period that ranges from 5-10 min depending on the type of engine. Therefore, even though an engine’s power is not necessary for taxiing, it is necessary that all engines must be running for a minimum of 5-10 min before takeoff. Thus, if the taxi time of an aircraft is less than five minutes, a single-engine taxi-out scenario would not change either the activities of the pilot or the surface emissions of that flight. Alternatively, if an aircraft taxies for longer than five minutes, the emissions are reduced by the amount of pollutants that one of its engines would produce for the duration of the taxi time in excess of five minutes.

This method is not done on uphill slopes or slippery surfaces, or when deicing operations are required as the asymmetric forces could push the aircraft off of its course and can even result in fatalities. Aircraft manufacturers like airbus and Boeing recommend that airlines adopt single-engine taxiing whenever conditions are favourable for it, and yet only a few airlines follow it. There is a potential for significant savings from single-engine taxiing; for example, American Airlines and Emirates airlines is estimated to save $10-$12 million a year by following this procedure.

On a recent survey conducted on single engine Taxiing at two different regions, 52% of pilots reported following the method more than 75% of the time, while they were infrequently used on departures and another 54% of pilots reported using them less than 10% of the time. The common Reasons are:

• Excessive thrust and related issues.
• Maneuverability difficulties, mostly related to tight taxiway turns and weather conditions.
• Problems involved in starting the second engine.
• Distractions and workload issues.

Towed Taxiing

Another approach that have been proposed to reduce fuel consumption and emissions is by shutting down all of the engines and running only the auxiliary power unit and towing aircraft to the runway, rather than using the engines to taxi. This procedure is also known as dispatch towing. During departure tow-outs, the engines are not turned on until five minutes before takeoff for warming up.

These aircrafts are then towed to the runways with the help of towing vehicles in the ground. As result, aircraft emissions are decreased. Although it was tried out in the past by Virgin Atlantic for their 747 fleet, the method had to be abandoned after Boeing advised that the nose landing gear on the 747s are not designed to withstand such loads on a regular basis. This concept is currently in development by Airbus, which is considering other means of dispatch towing in a way that will not involve imposing higher loads on the nose gear. Approximate yearly fuel cost reduction if every American Airline fleet were able to adopt this method: $1. 3 billion USD.

Shutting Down APU as much as possible at airports: Commercial aircrafts are equipped with a small jet engine mounted in the tail end that acts as a generator. When the main engines are shut down, pilots turn on this smaller engine, called the Auxiliary Power Unit (APU) to provide electrical power while the aircraft is at the gate. to operate things like the cabin lights and air conditioning. The APU also powers the systems that are used, to start the main engine. [image: ]The APU runs on jet fuel, so extended use of this results in increased consumption of fuel. An alternative to this is the usage of external ground power also known as GPU, that is Provided through a cable and is plugged to the aircraft. This ground power is generated much more efficiently and can power all onboard systems until it is time to start the engines, at which point the APU is started briefly. Average fuel reduction per flight: 11 gallons, $34 Image Source: www. aerospecialities. comContinuous Descent Arrival (CDA) Continuous Descent Arrival (CDA) or also known as Descent profile optimisation (DPO) is an aircraft landing technique in which an arriving aircraft descends from an optimal position with minimum thrust and avoids levelling up or step wise landing to the extent permitted by the safe operation of the aircraft.

In a conventional, non-CDA, approach the aircraft descends stepwise, with levelled flight in-between. But in CDA method, the aircraft remains higher for longer and with a reduced engine thrust. Both of these elements induce a reduction in fuel use, emissions and noise along the descent profile tll it reaches the point at which the aircraft is established on the final approach path. 1Image source: All Nippon AirwaysThe ideal CDA starts at the start of the descent and ends when the aircraft starts the final approach and follows the glide slope to the runway. Usually, CDAs are not possible all the time, not for all arriving flights and not always for the whole descent profile. But measures are taken at the airports to facilitate a higher percentage CDA to the extent possible.

Descending from a height of 6000ft can save up to quarter of a ton of fuel for a four engine aircraft if CDO method is used. Which will estimate to roughly 225USD per flight.

Improving the aerodynamics: Winglets

Winglets are pointy extensions at the end of the wings. It comes as a standard equipment in most of the newer airplanes. [image: ]Winglets helps to reduce the drag associated with the generation of lift. Which means that it allows the wings to be more efficient when creating lift, so that aircrafts require comparatively less power from the engines. This results in an increased fuel economy, lower CO2 emissions, and lower operational costs for airlines.

Winglets help to reduce the effects of “induced drag. ” Which means, When an aircraft is in flight, the air pressure on the immediate region above the wing is lower than the air pressure under the wing. So, in the region around the wing tips, the high-pressure air under the wing rushes to the low-pressure region on top. This results in the formation of vortices. The vortices flow over the wings and they pull air up and over the wing and they also pull air back. This is called induced drag.

With the advent of winglets, the aircraft is able to weaken the strength of wingtip vortices and cut down on induced drag along the whole wing. Boeing claims that winglets installed on its 757 and 767 aircrafts can improve its fuel efficiency by 5% and cut CO2 emissions significantly. An airline that installs winglets on its aircrafts consisting of 60 Boeing 767 jets is expected to save 500, 000 gallons of fuel annually.

A few other strategies followed by airline companies to save fuel

Reducing the usage of Thrust reversal during Landing: Airline pilots usually use the method of Thrust reversal during landing. The process reverses the thrust and the exhaust is pushed in the forward direction and produces deceleration. This method is used to reduce the stopping distance after landing in the runways. Although this can reduce the Brake pad wear out, it consumes a lot of fuel.

The airline pilots are advised not to use thrust reversal unless absolutely necessary e. g. , if the runway is too short to land without reverse thrust. Avoidance of reverse thrust can save approximately 13, 800 gallons of fuel per year per airplane.

Washing and Keeping the Engine Components Clean: Lumps of dust and dirt accumulates on the moving parts of the engine like compressor parts and reduce the efficiency of the engines and increase fuel consumption. So engine components are to be washed and cleaned regularly to maintain optimum performance of the engine. Cleaning and regular maintenance of engines have reduced fuel consumption by 17, 500 kiloliters per year.

Cruise Speed and Altitude Optimisation: Airplanes has to fly at optimum altitude to get maximum distance to fuel ratio. This is not always the altitude the aircrafts fly. By flying above or below these altitudes, aircraft experience higher than necessary fuel consumption. If every flight is operated at optimal altitudes when on air, the aircrafts could achieve a significant reduction in fuel consumption.

Average fuel reduction per flight: 23 gallons, $70 US Dollars. Total yearly fuel cost reduction if every fleet of American Airlines adopted to this change: $330 million

The same goes for cruise speed. The “cruise phase” of an aircraft is the segment of every flight after climb and before descent. Airline flights spend significant amounts of time in the cruise phase, almost 56% of total flight time is spent in cruise on domestic US Domestic flight operations.

However, commercial aircrafts rarely operate at a speed that maximizes fuel efficiency. For an aircraft carrying a particular amount of weight, there is a speed range that minimises fuel consumption and give best fuel economy.

The newest strategy is to encourage pilots to maintain that cruise speed. Average fuel reduction per flight: 20 gallons estimating $61 US Dollars.

The future

Another method of reducing the fuel consumption is reducing the fleet age, that is phasing out old aircrafts and bringing in newer aircrafts. Obviously newer aircrafts are cost effective and are much more fuel efficient. So purchasing of newer aircrafts will reduce the fuel consumption. It is known that the modern aircrafts are fuel efficient by almost 20 percent than the aircrafts in the 1980s. NASA and Boeing have developed a blended wing aircraft concept with a potential of being used for both commercial and military applications in the future. The design is called the Blended Wing Body (BWB). The BWB has a hybrid shape that resembles the shape of a flying wing, resembling a Stealth bomber aircraft but also incorporates features from an ordinary commercial aircraft. This combination offers several advantages over the conventional aircraft structure. The BWB airframe combines an efficient high-lift wings with a wide air foil-shaped body, allowing the entire aircraft to reduce the drag and generate lift. This shape also improves fuel economy and provide larger payload areas in the middle body portion of the aircraft.

The basic concept for a BWB was first introduced decades ago and variations of it have been used in the aircrafts like B-2 bomber (a blended wing) and YB-49. Like the B-2, the BWB design makes use of composite materials that are stronger and lighter than conventional metal parts. The BWB also has several control systems on the trailing edge for manoeuvrability, like the B-2, instead of the conventional tail assembly.

Because of its efficient design and construction, the BWB can save 20 percent more fuel than a conventional aircraft of similar configuration that is flying at cruise speeds of 7, 000 nautical-mile range. A BWB aircraft would have a wingspan slightly greater than a Boeing 747 and can be operated from most of the existing airport terminals. The BWB would also weigh less, will generate less noise and less emissions, and will have lower operational costs than an equally advanced conventional transport aircraft.

In just fifteen years, a plane that flies with a hybrid wing shaped body will become a reality. A scale version of the ‘Blended Wing Body’ (BWB) aircraft is being tested at a NASA facility now. NASA announced that commercial designs will be available by 2035.