Thirty-seven years of driving
The air up there in the clouds is very pure and fine, bracing and delicious. And why shouldn't it be? - it is the same the angels breathe. ~Mark Twain
The fuel required for our flight today is 12500 kilograms. Fuel is actually delivered in litres from the fuel truck, but converted to kilograms, because that is how fuel is measured in an airliner. The specific gravity of fuel is about 0.8. That is the ratio of one litre of fuel to one kilogram in weight. There are variables to this ratio, according to the atmospheric conditions of the day, but 0.8 is a good for today. With that ratio in mind, today we have ordered 15625 litres of fuel.
Not all of the fuel will be used on this flight. Airline flying has very detailed fuel requirements imposed on them by the regulating authority. We have to comply with their imposed criteria, however my airline has an even more stringent set of requirements, this bodes very well for passenger safety.
There are five portions of fuel planning that made up our requirement. There is; trip fuel, arrival fuel, alternate fuel, final reserve and contingency fuel. Our flight today is from Jomo Kenyatta, Nairobi to OR Tambo International Airport, Johannesburg. This takes into account the exact airframe we are using on the day. Some are a little bit older. some have different basic weights, some engines use more fuel per hour than others. Today our Boeing 737 has a basic empty weight of 30724 kg. When you add the fuel, cargo, three pilots and some catering, the take off weight comes to 49173 kg. That weight, together with the temperature, atmospheric pressure and wind on the day will require 9080 kilograms of trip fuel.
The arrival fuel at Johannesburg, is calculated by assuming the most likely route when within 50 nautical miles. There are many many aircraft from all different directions converging at Johannesburg to land. If you imagine a traffic circle which has five roads that feed it, the timing and spacing is crucial for success. Now factor in that aircraft are at different altitudes and different speeds. In order to streamline this arrival process, standard routings are created and flown from certain key points, 50 nm away from the airport. This will also give minimum altitudes and speed limits. This creates an orderly flow of aircraft, but also uses a little extra fuel than if we were to fly direct to the landing position. Today it is 340 kilograms.
Alternate fuel is used when the landing airport is not suitable for landing. This could be for several reasons. The most common reason is, either bad weather or the runway is temporarily closed. The planned fuel is the amount it will take to fly from overhead Johannesburg airport to King Shaka Airport, Durban and complete a full instrument approach. This too, takes into account the weight, wind and temperature. Our calculated alternate fuel for today is 1200 kilograms.
Next comes final reserve fuel. This is an equivalent of 30 minutes of flying time at cruise power setting, at 1500 feet above airfield elevation. The time is converted to kilograms for it to be useful. Reserve fuel is required to be in the tanks once the flight is completed. This fuel may only be used in an emergency.
The last portion of our flight plan is contingency fuel. Contingency fuel is complicated. It is for the unforeseen change in the wind, temperature or an unplanned weather diversion. There is a very sophisticated formula which is used, but suffice it to say, today we are working on 3%, which amounts to 272 kilograms.
These five portions of fuel add up to twelve thousand five hundred kilograms of fuel. I sign the book authorising the purchase of fuel. I have just spent approximatley R155 000.00 with a flick of my pen.
To put this all into perspective, I drive a small commuter car to and from the airport. My little silver Toyota Yaris has a fairly good fuel consumption. It also has a small fuel tank, 35 litres. The fuel uplift on today’s flight will give me a little over 446 tanks of fuel. I use on average, one tank of fuel per month for my daily running around. 446 tanks of fuel will translate into thirty-seven years of driving my little silver Yaris.