Fuel Grades and Fuel System Limits

Two things about this aeroplane's fuel surprise pilots converting onto it: the list of acceptable grades is long and unfamiliar, and the tanks hold less than the same airframe holds on AVGAS. Both follow from the fuel being kerosene rather than petrol.

At a glance

• Fuel gradesJET A-1 (ASTM 1655), JET A (ASTM 1655), Jet Fuel No.3 (GB 6537-2006), JP-8 (MIL-DTL-83133E), JP-8+100 (MIL-DTL-83133E), TS-1 (GOST 10227-86), TS-1 (GSTU 320.00149943.011-99)
• Alternative fuelsDiesel (DIN EN 590) and SASOL GTL Diesel
• Standard tanks2, each 67.55 l (17.85 US gal)
• Total fuel capacity135.1 l (35.7 US gal)
• Total unusable fuel15.1 l (4 US gal)
• Total usable fuel120.0 l (31.7 US gal)
• Low fuel caution light thresholdbelow 10 l (2.6 US gal) usable fuel per tank

Permissible grades

Seven grades make up the permissible list:

• JET A-1 (ASTM 1655)

• JET A (ASTM 1655)

• Jet Fuel No.3 (GB 6537-2006)

• JP-8 (MIL-DTL-83133E)

• JP-8+100 (MIL-DTL-83133E)

• TS-1 (GOST 10227-86)

• TS-1 (GSTU 320.00149943.011-99)

Two alternatives stand outside that group: Diesel (DIN EN 590), and SASOL GTL Diesel.

Capacity

Two standard tanks hold 67.55 l (17.85 US gal) apiece, so total capacity comes to 135.1 l (35.7 US gal). Subtract the 15.1 l (4 US gal) that cannot be drawn on and 120.0 l (31.7 US gal) remains usable.

Why the permissible capacity was cut back comes down to density: kerosene and diesel are heavier per litre than aviation gasoline (AVGAS).

Fuel selector limits

CAUTION — Down to 1/4 tank or below, running on the left tank alone or the right tank alone, sustained flight out of balance is prohibited.

CAUTION — Turbulence is a strong reason to select BOTH.

The low fuel sensors

Each tank carries a low fuel sensor. Fall below 10 l (2.6 US gal) of usable fuel in a tank and its own caution light comes on — "Fuel L" for the left, "Fuel R" for the right.

CAUTION — Air must not be allowed into the fuel system, so no tank is to be run dry. The moment the "Low Level" caution light comes on, either select whichever tank still holds enough fuel, or land as soon as possible.

Check yourself

• Name the two alternative fuels published for this engine.

• What is the total capacity, the total unusable and the total usable fuel?

• Why was the permissible tank capacity reduced?

• At what quantity per tank does a low fuel caution light illuminate?

• What is prohibited on a single tank with 1/4 tank or less remaining?

Study aid — always fly your aircraft's current AFM/POH.