How do you know which fuel an aircraft uses?

Question

Other than the decals on the plane, how would you know what fuel to use in an aircraft? Where is this limitation documented?

For some aircraft, does this limitation include some sort of substitute fuel for emergencies? For example, I have heard that if Jet A-1 is not available, some aircraft may have approved emergency fuels, such as AvGas.

Where would this information be found?

Answer 1

The actual fuel type limitations will be listed in at least two places: the aircraft type certification data sheet (TCDS), and the limitations section of the aircraft Flight Manual, Operating Handbook, or equivalent.

The fuel placards placed at the fuel filler ports might not list all approved fuels, or may state "Type X fuel only" when additional fuels may in fact be approved. These placards should be understood as a precaution against inadvertently fueling with an unintended or wrong type of fuel. In some cases ignoring these placards can have fatal consequences.

Some aircraft do indeed have approved emergency fuels. This information would also be found in the limitations listed above.

For example, the TCDS for the Beechcraft King Air B200 with PT6A series engines is lists the following for normal approved fuels:

Fuel JP-4, JP-5 (MIL-T-5624); JP-8 (MIL-T-83133); JET A, JET A-1, and JET B conforming to P&WC S.B. 1244 or ASTM SPEC. D1655; in addition for B200 and B200C Chinese No. 3 Jet Fuel. See NOTE 6 for emergency fuels

Note 6 in the TCDS reads as follows:

NOTE 6. Emergency use of MIL-G-5572: Grades 80/87, 91/98, 100/130, and 115/145 are permitted for a total time period not to exceed 150 hours time between engine overhauls. It is not necessary to purge the unused fuel from the system when switching fuel types.

Likewise, the EASA TCDS for the King Air B200 lists the same limitations.

The Flight Manual for the King Air B200 also lists these limitations, as applicable, as well as some additional altitude constraints when using emergency fuels due to electric boost pump requirements.

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In contrast to the actual fuel limitations, the placard placed at the fuel port for the King Air B200 lists very little of the actual limitations:

^{Source: Beechcraft King Air 200 Maintenance Manual}

Answer 2

As an example, the Cessna Caravan, with a PT6-114a engine can run on Jet A or other fuels, such as 100LL. The information is not always on placards. The POH is normally where this is documented. If a replacement engine has been installed, there will likely be a supplement with the STC which will cover alternate fuels and any limitations.

Pilots normally refer to POH and not maintenance manuals and type certification data. Therefore the POH or it's equivalent is the first place I would look. Besides, when you need to use an alternate fuel, the volumes of manuals and type certification data may not be readily at hand.

Addendum #1 Some aircraft, such as recip singles may have a STC permitting use of mogas, as an example. In these cases the STC will have an operations supplement for the POH or equivalent. This was actually a fairly common alternative fuel 20 years or so ago.

Answer 3

You know what fuel to put in your (light) aircraft, the same way as you know what fuel to put in your car - you've done it before and you know to lift the right nozzle at the bowser! For larger aircraft/airliners, chances are there is a person whose job it is to refuel your aircraft, and they will likely know very well what fuel to use. If they don't they would ask, or look up the correct fuel from somebody who does know.

There are a few things to help you remember, such as placards next to the fuel cap

The pipework/shut off at the bowser might also have a placards/indications/color-coding.

A for emergency fuel, that is part of flight planning - you calculate how much fuel you expect to use and add an amount on for emergency/contingency.

Answer 4

Placards only tell half the story, check the flight manuals for the rest of it

The placards at the fuel port will indicate what the primary or preferred type of fuel is:

• For spark-ignition reciprocating-engine aircraft, 100LL aviation gasoline is the primary certificate fuel, and that's what the factory placards will likely say. Some aircraft may have AFM or STC provisions for the use of other types of gasoline (such as other grades of avgas, or oxygenate-free mogas), but this will likely not be included on the placards.
• Aerodiesel (compression ignition reciprocating-engine) aircraft are typically fueled using Jet-A, and thus will have that on the placard. Some may be modified to use standard road diesel or blends of road diesel and jet fuel -- the placards won't mention this, but the AFM will.
• Smaller turbine (turboprop and jet) engines also are primarily fueled using Jet-A or a military equivalent fuel, and this will be on the placards. They can also often burn aviation gasoline or avgas/jet mixes but under operating restrictions that will be mentioned in the AFM.
• Large turbine engines will require jet fuel, and kerosene-based jet fuel at that -- they cannot run on wide-cut jet fuels such as Jet-B or JP-4, likely due to boiloff issues. These aircraft take enough fuel, though, that the only fueling systems capable of handling them are dedicated to jet fuel anyway.

Fuel ports help, but aren't the total solution

Jet fuel dispensers are supposed to use a wide, rectangular nozzle that is too big to fit into an avgas plane's fueling ports, thus preventing all but the most determined from misfueling an avgas-only plane with jet fuel. However, a few aircraft are retrofitted with turbine engines without changing the fueling ports, some older aircraft may have large diameter avgas ports due to the flows needed, and some turbine helicopters do not accept the standard jet fuel spout (J-spout or "Hoover spout"). Hence, some jet fuel dispensers are fitted with narrow "rogue" nozzles, creating the very misfueling hazard the J-spout is supposed to prevent.