The state in which the aircraft has become devoid of useable fuel.
This article explains the reasons for and the measures against fuel exhaustion.
Fuel exhaustion, is a situation where there is no more fuel onboard. Unlike Fuel Starvation there is nothing to be done about re-establishing the flow of fuel. Most of these occurrences lead to a forced landing or a ditching. Nevertheless, an ATSB study from 2015 (see Further Reading) showed that fuel exaustion results in fewer fatalities than fuel starvation. A possible reason for this could be that the pilots involved in fuel starvation scenarios consider more options than just a forced landing, sometimes leading to inappropriate choices and fatal outcomes.
Studies have examined the possibility of certain flight types being more prone to fuel related incidents. While fuel exhaustion accidents and incidents occur in all types of aviation operations and no firm conclusions may be drawn, there are a few aspects suggesting that certain operations are generally riskier in this regard as they are more vulnerable to any inaccuracies in the pilot’s knowledge about the amount of fuel on board. Examples of these are:
- Certain types of flight regularly carry just enough fuel for the flight, with little margin. Charter operations may be flying with minimum fuel required because a flight’s profitability will depend on carrying the maximum payload, which means no unnecessary fuel be carried.
- Experience on the particular aircraft type may be an issue in the private/business category as it leads to pilots being less familiar with the aircraft.
- Fatigue has been found to increase human error rates and may be a contributing factor to fuel-related events in the agricultural category where long working hours are the norm. Also, the high mental workload in agricultural operations may narrow their attention to tasks such as avoiding terrain and other obstacles as well as continually recalculating load requirements, resulting in reduced monitoring of the aircraft’s fuel system.
Exhaustion occurrences are normally either the result of a gross error in the fuelling of an aircraft before flight, or the result of a number of seemingly minor aspects of fuel planning and management during the flight. Incidences of fuel exhaustion often happen close to the flight’s destination and, if it occurs when the aircraft is close to landing, it may offer the pilot less time and opportunity to successfully manage the situation.
Causes and Contributors
The major causal factors for fuel exhaustion occurrences are pilot-related:
- Inaccurate pre-flight planning is the most common factor for fuel exhaustion events. Examples of this are:
- Incorrect assessment of fuel quantity. This includes both the amount of fuel on board, and the rate of fuel consumption. The chance of fuel exhaustion is reduced if the pilot accurately determines the amount of fuel on board prior to starting. This should entail the use of a fuel quantity crosscheck using a number of sources, including fuel quantity gauges, dipsticks, flowmeters/ totalisers and calculations from previous refuels and fuel usage, (regularly checked for accuracy).
- Miscalculation of fuel required. These included problems with, or not calculating consumption rates and not allowing for contingencies.
- Loss of fuel situational awareness
- Inattention to fuel supply.
- Deciding to continue with the planned flight regardless of being aware of a low fuel problem.
In addition to the above, it is common for training sorties to be flown with full tanks, or in situations where fuel does not become a real safety consideration. This may cause pilots to become complacent during their checking procedures, or to disregard warning signs when they occur. Behaviour patterns (good or bad) are often formed early in the training process. These patterns are often reverted to during periods of relaxation or stress. If pilots become complacent towards fuel management during the early stages of training, this behaviour, although it may not be typical of the pilot, may be reverted to later in their career in certain circumstances, with potentially fatal consequences.
The advise given in this section is to be considered as a general guidance against the most common causes of fuel exhaustion - inadequate pre-flight planning and poor inflight fuel management. It is not intended to replace the operator's Standard Operating Procedures (SOPs).
- Accurate fuel management starts with knowing exactly how much fuel is being carried at the commencement of a flight. This is easy to know if the aircraft tanks are full, or filled to tabs. If the tanks are not filled to a known setting, then a different approach is needed to determine an accurate quantity of usable fuel.
- The amount of fuel on board should be thought of, not as a quantity, but as a flight time. For a consistent combination of altitude, power setting and mixture setting, the fuel burn will be constant, but changing winds and deviations due to weather conditions will vary the groundspeed and therefore the range.
- The pilot in command must ensure that, before take-off, all of the following requirements are met:
- sufficient fuel is on board the aircraft for it to land at the end of the flight with the required fuel reserves still on board;
- the quantity of fuel in the aircraft’s fuel tank or tanks has been checked by visual inspection or by 2 different methods.
- Before an aircraft commences a flight, the pilot in command of the aircraft must plan the flight in such a way as to ensure that enough fuel will remain in the aircraft’s tanks after landing to allow it to fly for at least 30 minutes (or, for a rotorcraft, 20 minutes) at normal cruise power under ISA conditions at 1,500 ft above the place of intended arrival.
In-flight Fuel Management
Accurate fuel management relies on a method of knowing how much fuel is being consumed. Many variables can influence the fuel flow, such as changed power settings, the use of non-standard fuel leaning techniques, or flying at different cruise levels to those planned. If they are not considered and appropriately managed then the pilot’s awareness of the remaining usable fuel may be diminished.
- The fuel status should be regularly updated, at least every hour, to ensure that an adequate reserve is maintained. An aircraft that is carrying only just enough flight fuel for the planned flight, but which encounters unanticipated headwinds and perhaps has to fly at a lower level is eating into its fuel reserves. Those reserves are there to be used in unforeseen circumstances and many aircraft arrive safely at their destination having used a portion of the allocated reserve fuel. However an aircraft’s fuel supply should not reach a state where, upon arriving at its destination, it can accept no further delay.
- Aircraft flight manuals often provide data that shows the fuel consumption rate at standard power settings with the mixture leaned. If those settings are used, an assessment of the fuel remaining should be correct. However, even small changes in engine operating technique, such as leaning or a small increase in rpm, can make a big difference to fuel flow.
- Flights are planned on the basis of expected en route conditions. Monitoring a flight’s progress allows a pilot to assess if the flight is maintaining an adequate fuel reserve, and to make timely decisions if the flight conditions change.
- A fuel planning chart should be used and fuel flow/fuel used should be checked against planned values. Pilots should be alert for different fuel flow rates to that used in the flight plan. It is very important to be aware that time alone is not an accurate means of determining fuel remaining as consumption can vary with changed power settings, using non-standard fuel-leaning techniques, fuel leakage or flying at different cruising levels to those planned.
- The operator must establish a procedure to ensure that in-flight fuel checks and fuel management are carried out, and promulgate it in the Operations Manual.
- The pilot-in-command must
- ensure that fuel checks are carried out in flight at regular intervals. The remaining fuel must be recorded and evaluated.
- ensure that the amount of useable fuel remaining in flight is not less than the fuel required to complete the task with the specified reserve remaining.
- declare an emergency when the actual useable fuel on board is less than the reserve fuel.
- determine the last possible point of diversion to any en-route alternate if the flight is to an isolated aerodrome. Before reaching this point, they must assess the expected fuel remaining, the weather conditions, and the traffic and the operational conditions prevailing at both the destination and the en-route alternate aerodromes before deciding to how to proceed.
It is advisable to keep an accurate fuel record by logging at least the:
- quantity of fuel on board at start-up;
- time of starting up engine(s), and time of take-off;
- time of landing and time of shutting down engine(s);
- cruising level, power setting and TAS, with fuel flows and times for each significant phase of flight;
- any delays incurred;
- any holding;
- quantity of fuel on board after flight.
Accidents and Incidents
- RJ85, vicinity Medellín International (Rionegro) Colombia, 2016 (On 29 November 2016, a BAe Avro RJ85 failed to complete its night charter flight to Medellín (Rionegro) when all engines stopped due to fuel exhaustion and it crashed in mountainous terrain 10 nm from its intended destination killing almost all occupants. The Investigation noted the complete disregard by the aircraft commander of procedures essential for safe flight by knowingly departing with significantly less fuel onboard than required for the intended flight and with no apparent intention to refuel en route. It found that this situation arose in a context of a generally unsafe operation subject to inadequate regulatory oversight.)
- AT72, en-route, Mediterranean Sea near Palermo Italy, 2005 (On 6 August 2005, a Tuninter ATR 72-210 was ditched near Palermo after fuel was unexpectedly exhausted en route. The aircraft broke into three sections on impact and 16 of the 39 occupants died. The Investigation found that insufficient fuel had been loaded prior to flight because the flight crew relied exclusively upon the fuel quantity gauges which had been fitted incorrectly by maintenance personnel. It was also found that the pilots had not fully followed appropriate procedures after the engine run down and that if they had, it was at least possible that a ditching could have been avoided.)
- A332, en-route, North Atlantic Ocean, 2001 (On 24 August 2001, an Air Transat Airbus A330-200 eastbound across the North Atlantic at night experienced a double-engine flameout after which Lajes on Terceira Island in the Azores was identified as the best diversion and a successful glide approach and landing there was subsequently achieved. The Investigation found that the flameouts had been the result of fuel exhaustion after a fuel leak from the right engine caused by a pre flight maintenance error. Fuel exhaustion was found to have occurred because the flight crew did not perform the QRH procedure applicable to an in-flight fuel leak.)
- A310, Vienna Austria, 2000 (On 12 July 2000, a Hapag Lloyd Airbus A310 was unable to retract the landing gear normally after take off from Chania for Hannover. The flight was continued towards the intended destination but the selection of an en route diversion due to higher fuel burn was misjudged and useable fuel was completely exhausted just prior to an intended landing at Vienna. The aeroplane sustained significant damage as it touched down unpowered inside the aerodrome perimeter but there were no injuries to the occupants and only minor injuries to a small number of them during the subsequent emergency evacuation.)