Flying The Fuel Dollar Further

The savings start at the preflight stage. The concept of ‘fill ‘er up’ as a habit rarely prevails. Jet fuel is expensive stuff to airfreight, which is precisely what is being done to any fuel being carried unnecessarily. All responsible airlines have a minimum fuel reserve policy, usually backed up by the force of law. To this, the aircraft commander may add whatever additional reserve fuel is considered necessary on a particular day. When fuel was relatively cheap, it was easy to carry an extra few tonnes ‘for mum and the kids’ but in the present economic climate, a decision must be made as to what is really necessary. If the weather is forecast to be bad or if traffic congestion is expected, extra fuel should be carried; but on a fine day flying into an airport where only light traffic is expected, those few tonnes extra can reasonably be dispensed with at the fuel ordering stage. Every rule has its exception and there is one case where additional fuel should be carried. This occurs when the fuel at the next airport is so expensive that it is cheaper to airfreight some of the fuel for the next sector than it is to buy it at the next port. Remarkably enough this can produce in some cases of over one hundred dollars for every extra tonne of fuel carried after allowing for the cost of carrying it.

The potential for savings continues throughout the flight. Even when at idle thrust on the ground, a Boeing 747 consumes about 750 gallons per hour. Thus accurate judgement of start time with due consideration of delays due to other traffic can produce worthwhile savings. Starting the engines during the pushback rather than at the gate beforehand, saves precious minutes, and gallons of fuel. Avoiding stop-start taxiing with a little anticipation of traffic conflicts produces similar savings as quite a lot of power is required to get a heavy jet aircraft moving again once it has stopped.

In flight, the rewards for good technique continue. Once clear of the runway and of any obstacles in the take-off flight path, it pays to clean the aircraft up as soon as safely practical. Flaps and leading edge devices, essential for the take-off, rapidly become a drag creating hinderance as speed builds up and should be retracted fairly expeditiously to allow for an efficient climb. Climb speeds should be adjusted to allow for aircraft weight; a lighter aircraft can be climbed at a lower speed without approaching the back of the power curve.

Cruise speeds must also be adjusted to allow for aircraft weight and cruising altitude. It is not always possible to cruise at the optimum altitude for the aircraft weight, due either to other traffic, airspace restrictions or adverse winds at that altitude. A small speed change, costing less than one minute per hour of cruising flight, can sometimes make a difference of one or two per cent in fuel burn Aircraft commanders, aided by modem area navigation systems, are alert to the possibilities of direct clearances to remove some of the doglegs in the airways system when there is no conflicting traffic. Air traffic authorities are assisting in this process by providing direct area navigation airways to allow suitably equipped aircraft to track directly over long distances rather than to fly a meandering course from radio beacon to radio beacon. Every mile not flame saves about six gallons of fuel in the Boeing 747. This may sound a small saving until one considers the savings spread over a large fleet of aircraft each of which flies around 1. 5 million miles per year.

The descent phase of flight is one which requires some judgement to extract the maximum savings. The normal descent in a large jet aircraft is flown at idle power down to the airport traffic area if possible. Any engine thrust that becomes necessary to adjust this descent path consumes more fuel so the selection of the correct descent point with due consideration of the expected wind components during descent and the number of track miles to the final approach becomes a point of professional pride to most airline pilots. Unfortunately, all the planning in the world can be undermined by the constraints of weather and air traffic control.

During approach and landing a fuel efficient approach is also usually a quiet one. If the flaps and undercarriage are extended too early, large amounts of engine thrust are necessary to counteract the drag caused by these devices, consuming extra fuel and creating extra noise. It is more fuel efficient to gradually and progressively reduce speed and deploy the high lift devices throughout the approach, provided of course that the last stages of the approach are flown in a stable configuration.

Once back on the ground savings can again be enjoyed through use of careful taxiing techniques. At the terminal, the use of the auxiliary power unit which burns around one hundred gallons of fuel per hour can be varied according to conditions. If the aircraft is to remain at a port for several hours without passengers on board, it is not really necessary to operate the air conditioning for all that time so it is cheaper to just use a source of ground power to maintain essential electrical services and lighting. As long as the air conditioning is restored at a suitable time before the next flight, dependent on the outside air temperature, the cabin will be at a comfortable temperature with considerable fuel having been saved.

Any of the measures referred to in the preceding paragraphs when taken in isolation will only produce a small saving, however with due care and attention, that elusive one per cent can be achieved. And when that one percent can be translated into several million dollars, the saving becomes very worthwhile indeed even before taking into consideration the conservation of a finite resource.