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The state in which the fuel supply to the engine is interrupted, although there is adequate fuel on board the aircraft. - Source: ATSB
This article compares the terms "fuel exhaustion" and "fuel starvation", elaborates on the causes for starvation and gives some recommendations on its prevention.
Starvation Vs. Exhaustion
Fuel starvation and fuel exhaustion share the same possible outcomes:
- Engine failure
- Forced landing
- Controlled Flight Into Terrain (CFIT)
The difference is that in the exhaustion case there is no fuel remaining on board (for whatever reason) while with starvation there is (sometimes enough) fuel but for some reason it cannot reach the engine. It is therefore possible in some cases to re-establish the flow of fuel and to regain engine power.
Causes and Contributors
There are three major causal factors for fuel starvation occurrences:
- Pilot factors. These are the most common cause for fuel-related occurrences.
- Fuel Mismanagement. This occurs when the pilot forgets to switch fuel tanks when necessary, or switches to the wrong fuel tank, or just doesn’t monitor the fuel burn during a flight. Much of the time, the problem stems from a lack of understanding of the fuel system itself.
- Lack of familiarity with the aircraft, or lack of experience on the particular aircraft type.
- Distractions. There have been aircraft accidents in the past in which the pilots allowed a fuel starvation event to occur while preoccupied with something else, like fixing a landing gear problem or becoming disoriented. The adage applies here: Aviate, navigate, communicate — in that order. Troubleshooting or allowing yourself to get distracted by other people or events can lead to fixation on that particular problem or event and can cause the pilot to completely disregard other important aspects of the flight — like fuel management.
- Mechanical Problem or Failure. Very rarely, there is actually a fuel leak or a problem with the fuel system that can cause fuel starvation. In these cases, early recognition is key to dealing with the problem. Monitoring the actual fuel burn and the status of the fuel system is essential. The most commonly occurring technical factors are:
- Component failure (most frequently a problem with the fuel lines, fuel gauges, filter or carburettor)
- Malfunctioning fuel system (most frequently caused by a vapour block or a faulty fuel pump)
- Design-associated factors (such as owner’s manual details, fuel system and engine control design) when combined with pilot factors (e.g. lack of familiarity with the aircraft) may sometimes lead to fuel-related events.
Studies have found that there are some specific aspects of fuel-related events that may arise from the types of operations or pilot experience:
- In relation to pilot experience, research has found no relationship between the total hours flown and involvement in fuel-related occurrences. A relationship has been found, however, between hours on the specific aircraft type and involvement in fuel related occurrences. That is, pilots with fewer hours on type tended to be involved in a greater number of fuel-related occurrences. Regular Public Transport, commuter and training operations were found to have experienced fewer occurrences than were expected given the hours flown in each category. On the other hand, private/business/general aviation operations were found to have been responsible for a disproportionately large number of fuel-related occurrences.
- Fatigue has been found to increase human error rates and may be a contributing factor to the high rate of fuel exhaustion and fuel starvation accidents within the agricultural category where long working hours are the norm. Alternatively, the high mental workload experienced by pilots 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. Still, caution must be used when drawing any conclusions about the relative safety of any operations category.
Good knowledge of the performance and characteristics of the aircraft, as well as comparison between the information in the logbook, gauges and the level in the tanks are necessary to avoid fuel starvation. These elements are an essential part of flight preparation. Good fuel management during the flight will then allow the right decision at the right time: to divert or continue the flight.
Since most fuel exhaustion events can be attributed to pilot factors, the following fields offer greatest opportunities for improvement:
- Pilot training and procedures
- The establishment of an education program, emphasising the importance of the pilot’s responsibility for fuel management checks;
- Demonstration of fuel system management knowledge and skills as an essential requirement for the Biennial Flight Review (BFR) and routine flight checks;
- Standardisation of fuel selection and management systems within operators’ fleets;
- Consideration of ergonomic and procedural issues in aircraft fuel systems, when determining airworthiness standards.
- Flight preparation
- Route study, possibility of refueling at a stopover, study of meteorological dossier, study of NOTAMs, fuel assessment (consideration of aerodromes for diversion)
- Knowledge of aircraft (performance and consumption) as well as aircraft characteristics (characteristics linked to refueling, visual check, selectors ...)
- Update of information: pre-flight check, weather update, quantity of fuel remaining, quantity of fuel added, total quantity loaded, comparison of data from the log-book, visual check, information from gauges, etc.
- In-flight fuel management
- Fuel check - precise knowledge of flight time elapsed; tank selection
- Re-planning of flight - choice of diversion aerodrome and new fuel assessment
- In case of a critical situation
- Decision to abort the flight before running out of fuel completely
- Precautionary landing
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.)
- C310, Hawarden UK, 2013 (On 15 November 2013, a privately operated Cessna 310 about to land at Hawarden crashed after power was lost from one engine and the experienced pilot appeared to have attempted to initiate a go around rather than land on the grass next to the runway. The Investigation found that both main fuel tanks were effectively empty after normal fuel use during the flight and since unused fuel remained in the auxiliary tanks, it was concluded that fuel starvation attributable to en route fuel system mismanagement had occurred. The other engine had been at full power but with fuel starvation imminent.)
- EC35, vicinity Glasgow City Heliport UK, 2013 (On 29 November 2013, control of an Airbus Helicopters EC135 undertaking a night VMC night for policing purposes was lost after both engines flamed out following fuel starvation. The subsequent crash killed the three occupants and seven on the ground, seriously injuring eleven others. The Investigation found that although the pilot had acknowledged low fuel warnings after both fuel transfer pumps had been switched off, the helicopter had not then been landed within 10 minutes as required. No evidence of any relevant airworthiness defects was found and without FDR/CVR data, a full explanation of the accident circumstances was not possible.)
- LJ24, vicinity Bornholm Denmark, 2012 (On 15 September 2012, a Learjet 24 experienced double engine failure in daylight VMC as it positioned visually on base leg at Bornholm and an emergency was declared. The subsequent handling of the aircraft then led to a stall from which recovery was not possible and terrain impact occurred in a standing crop at low forward speed shortly after crossing the coastline. The aircraft was destroyed and both occupants seriously injured. Investigation established that the engines had stopped due to fuel starvation resulting from mismanagement of the fuel system and had been preceded by a low fuel quantity warning.)
- B772, London Heathrow UK, 2008 (On 17 January 2008, a British Airways Boeing 777‑200ER crash-landed 330 metres short of the intended landing runway, 27L, at London Heathrow after a loss of engine thrust on short final. This un-commanded reduction of thrust was found to have been the result of ice causing a restriction in the fuel feed system. Prompt crew response minimized the extent of the inevitable undershoot so that it occurred within the airport perimeter.)
- A346, en-route, Amsterdam Netherlands, 2005 (On 8 February 2005, a Virgin Atlantic Airways A340-600 experienced in-flight fuel management problem which led to loss of power of No 1 engine and temporary power loss of No 4. The captain decided to divert to Amsterdam where the aircraft landed safely on three engines.)
- Aircraft Fuel Systems
- Fuel Management
- Flame Out
- Fuel Starvation, Stress, Fatigue and Nonstandard Phraseology (OGHFA SE)