An agricultural pilot’s fatal crash shines the spotlight on unapproved fuels.
On 18 October 2013, the pilot of an Ayres S2R Thrush was going through the daily grind of aerial spraying in Western Australia. After a full morning’s work and lunch, he resumed the afternoon’s spraying. When the Thrush did not return as expected, the ground crew grew concerned and began an aerial search. They found the wreckage and the pilot’s body 1700m from the airstrip.
The Australian Transport Safety Bureau report said the crash occurred as a result of a departure from controlled flight, from which the pilot was unable to recover. Although the ATSB did not find a definitive cause for the crash, it noted that one factor that increased risk was the use of unapproved fuel. The other increased risk factor was one of ‘the usual suspects’: the aircraft was loaded beyond maximum allowable weight, with a centre of gravity beyond limits.
This particular Ayres S2R Thrush was powered by a Garrett TPE 331-5-252M turboprop engine, running a 70/30 mix of diesel and aviation turbine fuel. Honeywell Aerospace, which owns Garrett, does not approve the use of diesel fuel in this engine. The ATSB said: ‘The engine manufacturer had significant concerns regarding the use of diesel in its engines and identified a number of adverse effects of both short and long-term usage.’
So what is an approved fuel?
There are two issues with using non-aviation fuel in an aircraft: whether the specification of the fuel meets aviation standards, and whether the batch of fuel meets specifications.
Simply put, an approved fuel is a designated specification of fuel that is listed in a manual or manuals provided by the aircraft (or aircraft engine) manufacturer, for example the aircraft flight manual or engine type certificate data sheet. The term ‘diesel’ is a very ambiguous one that can cover a wide range of fuels created by the refinement of crude oil. It could refer to automotive diesel, No. 1 Diesel, No. 2 Diesel, or several others.
Diesel fuels vary in a number of respects, including flash point; cloud point; water and sediment; carbon residue; ash; distillation; viscosity; sulphur; copper corrosion; cetane number; cetane index; aromaticity; lubricity; and conductivity.
The question should not be whether diesel fuel is approved for use in a particular aircraft, but rather what specification of diesel (under the ASTM D975 classification) is approved for the aircraft in question. The answer is in the appropriate, approved data for each aircraft/engine combination. CASA Airworthiness Bulletin 28-015 is a more technical discussion of the appropriate diesel fuel specification for aircraft.
To further complicate matters, even if the specification of fuel carried on board is approved, it does not mean that the fuel is of the quality necessary for operation of the aircraft. Fuel not stored properly, or beyond its intended useful life, can go off, losing the physical characteristics needed to behave as intended in the aircraft’s engines. Cladosporium resinae, a fungus commonly referred to as clad, can infiltrate carelessly stored diesel fuel, reduce its quality, and potentially result in the engine stopping completely during operation.
What can I do to make sure that the approved specification of fuel is on board, and its quality is up to scratch?
CASA CAO 20.9 says ‘the pilot has responsibility for the fuel they have caused to be delivered to an aircraft’. So as the pilot, it is important you understand the two compounding issues of the correct specification, and the quality, of that fuel. Being present during refuelling, performing the correct fuel drainage procedures in accordance with the aircraft’s manuals, planning ahead by determining what fuel specifications are stored at any airfield being used for refuelling etc. should all be taken into account before any flight. Always refer to approved data for the aircraft when making any decisions.
Although the regulations place the responsibility for fuel squarely on the pilot’s shoulders, this does not preclude the operator from helping. Any operator can implement processes and procedures for the storage and maintenance of fuel that will assure its quality is preserved. Even something as simple as only using reputable fuel suppliers will reduce the possibility of low-quality or wrong specification fuel being pumped into your aircraft.
Making sure that you are informed of the correct and approved practices for refuelling is the best way to keep your aircraft and you safely in the sky.
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