tank/cell tested by a gas-free engineer to ensure
4. You should always ground the aircraft to
the tank/cell is safe for personnel to initiate
an approved grounding point. The aircraft must
depuddling. If after this time a "safe" condition
be bonded to the defueler. The grounding cable
is not reached, reinstall the air blower for at least
for the nozzle must be grounded to a metal part
an additional 15 minutes and have the test
remote from the tank/cell. This minimizes static
repeated. Continue the venting and testing, if
necessary, until the tank/cell can be certified safe
Then you attach the bonding cable from the
for personnel. The air inside the tank/cell has to
nozzle to the aircraft.
be certified and documented as safe. The outside
5. Personnel requirements are one person to
safety observer and the individual who is going
man each fire extinguisher, one to operate the
to enter the tank/cell should obtain all the
defueler, and one person to operate the aircraft
necessary protective clothing and equipment and
defueling panel. You also need one person to
proceed with the depuddling.
operate the fuel system control panel inside the
aircraft, if applicable.
NOTE: The two individuals should always
be connected by a safety line in case of an
The next step in depuddling is to remove all
the necessary access panels and covers required.
Do not defuel aircraft in the vicinity of an
Then, immediately after entering the tank/cell,
electrical storm. No maintenance of any
the individual must cap or seal all openings leading
type will be allowed on the aircraft during
from other possible sources of fuel or fuel vapors.
Depuddling can be accomplished by using an
approved explosionproof vacuum cleaner. You
can also use a cellulose sponge or cheesecloth to
ing fuel from low-point drains into an approved
remove the residual fuel from the tank/cell.
When you perform maintenance on a fuel
Depuddling of the aircraft fuel tank/cell is a
tank/cell, the next step is purging. There are now
hazardous operation because it requires the entry
four approved methods you may use to purge the
or partial entry of personnel into an aircraft
aircraft fuel tank/cell. They are the air blow, air
tank/cell. They remove any residual fuel that was
exhaust, oil purge methods, and JP-5 method.
not removed from the tank/cell during defueling.
The air blow purging method uses an air
In an effort to minimize the hazards associated
blower and ducting to force fresh outside air into
in depuddling, all maintenance personnel are
the tank/cell. The air exhaust purge method uses
required to work in pairs. One person should
an air blower and ducting to draw fresh outside
remain outside the tank/cell to act as a safety
air through the tank/cell. The oil purge method
observer while the other actually enters the
uses lubricating oil, MIL-L-6081, grade 1010, to
tank/cell to do the depuddling. The following
dilute the fuel vapors in the defueled tank/cell.
general safety precautions apply to depuddling:
The oil purge method is the most desirable of the
The aircraft battery connector and aircraft power
three methods. It is necessary to perform extensive
receptacle should always be tagged with an
repairs to the aircraft other than maintenance
appropriate warning placard. This is to indicate
solely related to the fuel system. The oil purge
power is NOT to be applied to the aircraft under
method will normally keep the tank/cell safe for
any circumstances. Before you perform any
personnel for approximately 10 to 15 days. The
depuddling, refer to the aircraft maintenance
JP-5 method uses JP-5 fuel to dilute and help
manual and NA 01-1A-35 for the proper support
remove all residues from low flash point fuels
equipment that must be used.
including JP-4 or AVGAS.
When you purge a tank/cell, attach an
NOTE: In all methods of purging, it is
approved air blower to the tank/cell and ensure
mandatory that the tank/cell be certified.
that all personnel remain clear of the removed
This is done by a gas-free engineer and
access panel. After allowing approximately 30
documented as being safe for personnel or
minutes for the blower to remove the toxic vapors,
safe for hotwork.
you should stop the air blower and have the