Fuel management is critical for flight operations especially when aviation is filled with uncertainties of changing enroute weather, runway closures and in-flight technical snags – often requiring pilots to remain in air for longer period than estimated. At busy airports, the uncertainities begins on ground when planes have to hold on taxiways for extended periods after leaving the gates.
Cost of fuel is a major part (approx 40 %) of operating cost of an airline. Therefore, airlines across the world try to economise on fuel consumption. Goes without saying that – lesser than required fuel onboard would make the fight unsafe. However, excess fuel on board is commercially bad for the airline as it imposes weight penalty and increases fuel burn. It also defeats the global initiative to go green by burning as less fuel as possible. Fuel planning is therefore a critical activity for aviators …… and a topic of interest for passengers.
Fuel planning is an integral part of preparation for the flight – called Pre-Flight Planning. The minimum quantity of fuel that must be uploaded is worked out on a ‘worst case scenario’ basis. Airlines across the world follow a standardised format issued by ICAO. However, in the interest of enhancing safety, the Airlines and the Pilot in Command are always at liberty to carry more than the minimum fuel prescribed by regulations.
Standard Fuel Planning Format
Let us assume that you are travelling from Airport A (departure Airport) to Airport B (destination Airport). As a part of flight planning, your airline adds an alternate / diversion to Airport C to cover for contingency of inability to safely land at the Destination Airport (B).
Graphically, our journey can be represented as follows. In normal course, it should comprise of Taxi to the runway, takeoff, climb, cruise, descend and landing at the destination.However, there are uncertainities in this plan which we shall discuss in details in a moment.
Before that, let’s have a look at a typical fuel plan and we shall try to make sense of it in the subsequent paragraph.
The heading on the left in the encircled area are essentially the ‘Phases of flights’ that you come across as you fly from your departure airport till you land back at the destination or the Alternate Airport. The fuel quantity is broken down to cover all phases of flight as follows-
This is the fuel required to Taxi from gate to the runway end at departure airport. Taxi times can be large at bigger airports. To add to this, busy airports require you to hold at the runway end for extended periods before you can actually take off.
In addition, taxi fuel also includes the fuel required to run the Auxiliary Power Unit (APU – a smaller engine in the aeroplane) to provide airconditioning & lighting while passengers are boarding, for pilots to carry out preflight checks and for the ground staff to carry out loading and maintenance.
The comprises the major part of the fuel requirement. It includes the fuel used for Take off, climb, cruise, descend and landing.This fuel is meticulously planned by taking the winds and weather into consideration.
It is estimated as 5 percent of the trip fuel. It caters for weather related rerouting, changes in winds enroute, reduced fuel efficiency of older engines and other miscellaneous factors.
Ideally, the Taxi, Trip and contingency fuel should be enough to take us to our destination. What if the runway at the Destination (B) becomes unusable just when your aeroplane is about to land?
No worries, pilots carry additional fuel to abandon the landing at the destination airport (B) and head for the alternate airport (C in our case). This is called Alternate Fuel. It caters for a missed approach at Destination (B), climb and cruise towards Airport C, descend and land at the Alternate Airport C.
Whenever diversions become necessary, a lot of aeroplanes have to divert. This temporarily overloads the Alternate airport. What if the runway at the Alternate airport C is temporarily unavailable due to operational issues? Do the pilots plan to arrive at the alternate airport with a dry tank? No, never. To cater for this eventuality, the pilots carry some more fuel (called Final Reserves) which allows them to circle over the alternate airport for 30 more minutes if required before landing. Pilots rarely use their reserve fuel as help comes from all sectors much before that. An aircraft which is low on fuel declares an emergency to gets priority handling from ATC and is provided all assistance to land expeditiously.
The Pilot in Command is eventually responsible for safe conduct of flight. The Captain of a flight is at liberty to uptake extra fuel (over and above the above stated fuel) based on his judgement. This is usually based on known conditions at the arrival airport. For example, airports in commercial capitals and big cities are known to have Air traffic congestion in the morning and evening as more aeroplanes try to arrive in the morning and leave in the evening with business travellers. This usually results in excessive hold time in air during peak hours. The pilots in know of this factor take the discretionary fuel to cater for the delays.
Inflight Procedures for Safe Conduct of Flight
While in air, the Pilots regularly monitor the fuel consumption and compare it with the data (Computerised Flight Plan) provided to them by the Airline office. Any discrepancy is seen as a concern and the pilots take prompt action to decide the safe course of action and land at the nearest enroute airfield.
Modern aeroplanes have a advanced electronic system for measuring fuel. In addition, the Flight management Computer makes all calculation taking the load off the pilots head. Modern FMS also warn pilots with text messages in case of impending situation like insufficient fuel for the intended airport.
Can Pilots make mistakes in calculating the required amount of fuel?
Worldwide, different units are used to measure fuel quantity.Some countries measure fuel quantity in Kiligrams while others may do it in Pounds. Measurement in Gallons are also common in USA. Invariably, the fuel Bowser operators and technicians of the visiting airport use the locally prevalant measuring unit. Since pilots fly across countries and refuel anywhere enroute, the pilots are required to be careful about conversion so that the tanks are correctly refuelled for the next flight.
Fuel Leak and Fuel Dumping
Fuel is carried in tanks in both the wings and the fuselage of the aeroplanes. The fuel is carried to engines through extensive network of pipelines and joints. The fuel system can be broadly divided into two isolated fuel system – on the left and right side which feed their respective engines. There is a remote possibility of fuel leaking from any of the points in the fuel system. In order to ensure that the fuel does not leak out completely, the pilots have controls in the cockpit to isolate the faulty tank or one of the side from the other.
However, not every fuel discharge from aeroplane is a fuel leak. Many a times (in long haul planes), fuel is deliberately dumped from the wings to lighten the plane for an unscheduled landing enroute (say for medical emergencies on board).
Fuel Management is critical activity for safe conduct of flight. Despite the crowded skies, busy airports, vagaries of weather and ongoing effort to be commercially viable – the joint effort by the workforce on ground, the pilots and the ATC ensure that aeroplanes never go or return thirsty for fuel !!
About the Author
Wing Commander K Dinesh is FLIGHT ANXIETY CONSULTANT. He is a former Indian Air Force officer and the founder of Cockpit Vista, an innovative Aircraft Simulator based set up in Mumbai (India). He provides Aviation Safety Consulting with emphasis on Flight Anxiety Removal amongst air travelers using a full size Aircraft Simulator. The Simulator is also utilised by pilots and Corporates.
For details / booking please visit www.cockptvista.com or call +91 9833892747 (India)
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