1 Examine all accessible fuel cell interconnects, fuel cell access covers, drains, boost pump mounting
points, and fuel line connections. Follow periodic instructions given in applicable aircraft maintenance technical manuals.
2 If the aircraft has not had an engine run-up, operate fuel boost pumps keeping main fuel shutoff
valve closed. Check for leaks in the lines upstream of the main fuel shutoff valve.
Leak detection for engine runup. If engine runup or test flight is programmed, the leakage test may be
conducted any time after the aircraft has been fueled. Only yellow dyed fuel may be used for engine runup testing on the
ground, after an engine change, or for test flights after a periodic or phased inspection. The dyed fuel is particularly
useful in checking for leakage near the engine hot section area, where high temperatures prevent leaking fuel from
leaving a wet spot. When the dyed fuel evaporates from a surface, the dye remains as a deposited residue.
Perform engine runup or test flight in accordance with applicable directives.
Upon completion, carefully examine main fuel line shutoff valve connections and all other
connectors downstream from it. Any dye deposit indicates leakage.
Dry-cleaning solvent is flammable and solvent vapors are toxic. Use P-D-680,
Type II Solvent in a well-ventilated area. Keep away from open flames. Avoid
prolonged solvent contact with skin.
When a leak has been repaired, remove the dye stain with the aircraft fuel or dry-cleaning solvent
conforming to P-D-680, Type II, and repeat the applicable test. Recheck repaired areas to verify leakage has been
(h) Disposition of dyed fuel. JP-4 fuel dyed with yellow dye may be left in the fuel system, following leak
detection operations and used in normal operations.
1 Yellow dyed fuel which must be removed from the fuel system may be placed in bulk storage and
used without dilution or mixed with other dyed fuel which has been diluted.
JP-4 fuel dyed with red dye liquid will be diluted in the aircraft 10 to 1 with undyed fuel and used in
normal operations or removed from the aircraft and placed in bulk storage where it is diluted 10 to 1 with undyed fuel.
This fuel may then be issued to base assigned aircraft for normal use.
3 The bulk tank in which the dyed fuel is stored or mixed with standard fuel will be marked with signs 4
x 12 inches, black letters on white background, which will be prepared using wood or similar material. The signs will
read: THIS TANK CONTAINS LEAK DETECTION DYED FUEL. These signs will be temporarily attached to the
receiving and issuing valves. When all of the dyed fuel has been issued, the signs will be removed. This should be
accomplished in order to avoid confusion with colored gasoline.
4 Any excess liquid stain on aircraft, fuel cell, or storage equipment may be removed by wiping with a
cloth. The dye will lose color over a short period of time; therefore, it is not necessary to take special measures to
remove all stains.
(i) Servicing procedures to transient aircraft. Dyed fuel stored in bulk storage facilities will be serviced to
locally assigned aircraft. It will not be serviced to transient aircraft. The presence of dyed fuel in transient aircraft could
be falsely construed by air crews and maintenance personnel as contaminated fuel. If emergencies arise requiring
servicing of dyed fuel to transient aircraft, the crew will be advised and note made on aircraft form that aircraft was
serviced with dyed fuel.
Approved testing fluids. The following approved calibrating fluids and their uses are listed as follows:
Equipment calibrated with MIL-C-7024 Type I will not be operated using other
fluids. Incorrect calibration may result.
MIL-C-7024, Type I is used to test switches on aircraft using AVGAS.
MIL-C-7024A, Type I is used to test fuel system components for reciprocating engines.
MIL-C-7024, Type II is used to test switches on aircraft using jet fuel.