A very small leak may require an hour or more
for color to appear. If no coloration appears after
a reasonable waiting period, fill the tank to the
two-third level. Add another 2-ounces of dye for
Prior to an inspection, entry of personnel, or
each 100 gallons of fuel added. Wait as before.
repair of any fuel tank/cell, specific functions
Again, if no coloration appears after a reasonable
must be accomplished. These functions are
waiting period, repeat the process at full tank
discussed in the following paragraphs. A defini-
capacity. The dye will leave a stain, which can be
tion of each function is provided to allow you to
traced to the source of the leak even after the tank
become familiar with it.
unit has been emptied.
1. Defueling. Defueling is the process of
removing fuel from the aircraft tank/cell.
NOTE: Do not return the colored fuel to
2. Depuddling. Depuddling is the process of
bulk tanks or trucks, as there is sufficient
removing residual fuel from cells/tanks after
dye in a 2-ounce can to color 10,000 gallons
necessary step prior to air purging when a non-
toxic and noncombustible atmospheric state is
The colored fuel is suitable for use in aircraft
required in a fuel cell or tank.
engines since the dye does not have a harmful
3. Purging. Purging is the process for
effect on the usefulness of the fuel. If you do not
removing fuel vapors capable of producing a
empty the aircraft fuel tank to repair the leak, the
combustible or toxic atmosphere.
dyed fuel can be burned in the engine. Fuel from
tanks tested with dye will remain colored until the
tanks have been filled and emptied several times.
or purging on an aircraft, you park it in an area
Stains on the aircraft structure or clothing can be
specifically authorized for such operations. You
removed with aircraft fuel or an approved dry-
must be familiar with the safety precautions and
procedures listed in the maintenance instruction
manuals and NAVAIR wing and squadron
Preparation for Fuel Cell Maintenance
Before any maintenance is performed on a fuel
tank/cell, a check of the applicable aircraft
General defueling precautions of aircraft
maintenance manual is required. If the aircraft
include the following:
maintenance manual is not specific enough to
cover the type of maintenance that is required,
refer to the Aircraft Fuel Cell and Internal/
1. Position the aircraft at least 100 feet from
External Tank manual, NA 01-1A-35, for
any building or smoking area or in the designated
additional information. If you find conflicting
2. Fire extinguishers must be inspected for
information between the specific fuel system
serviceability and manned at all times.
portion of the aircraft maintenance manual and
the NA 01-1A-35, the procedures in the NA
3. The defueler must be parked as far from
01-1A-35 manual take precedence.
the aircraft as possible. It should be parked
heading away from the aircraft in case it becomes
necessary to move the defueler in an emergency.
To protect personnel from the health hazards
associated with aviation fuels, protective clothing
and equipment are required and should be the first
priority before starting any fuel cell maintenance.
Specific items such as respirators, coveralls,
All the required grounding and bonding
proper shoes, and safety goggles are usually
cables must be attached before the aircraft
available for use by personnel. All of these are
or defueler tanks are opened. Bonding and
required to work with aviation fuels cell or tanks.
Appendix B of NA 01-1A-35 contains specific
grounding wires must be attached to clean,
unpainted, conductive surfaces to be
information on all of the required safety equip-