Inspect for lack of adhesion by applying air at a maximum of 100 psi with an air gun placed approximately
1/2 inch from the sealant. If loose sealant is found, cut through the sealant and strip by pulling away from the structure.
Strip sealant until it breaks rather than pulls away from the tank structure. Take extreme care not to damage the
structure or the corrosion control coating.
Check for loss of luster, discoloration, chalking or loss of topcoat.
Inspect for loss of elasticity by firmly pressing sealant with a blunt metal punch of not less than 3/16 inch
diameter. The sealant is good if it gives and returns to its original position; it is defective if the sealant breaks and holds
its pressed position.
7 Inspect for loose, cracked, or missing fasteners.
Visible defects in sealant or the structure are not necessarily the source of a true leak.
Continue visual inspection until the entire suspected leak area has been carefully inspected.
Mark all defects.
Cells. Inspect fuel cells for wear and damage. Refer to tables 2-5 and 2-6 for serviceable limits.
Maintenance. Maintenance for fuel tanks and cells includes inspection for damage and leak testing. Tank
sumps must be drained prior to flight to remove any contaminants. Fuel tank strainers must be cleaned and inspected on
a regular basis. Fuel tank pumps must be replaced as required. All repairs should be made in accordance with the
applicable aircraft maintenance manuals.
Purging. Fuel cells may be purged and preserved by either of the following methods. The method to be
used will be determined by the availability of preserving oil, equipment, number of aircraft involved, cost of preserving
agent, availability of C02 or nitrogen gas, time, manpower, and skills available to perform the operation.
Primary method. If an adequate supply of lubricating oil, MIL-L-6081, grade 1010, and the necessary
defueling equipment is available, purge and preserve the fuel cells as follows:
· The aircraft and all equipment used in performing the purging operation must be properly
grounded. This includes defueling equipment, work stands, purging equipment, and any
powered or pneumatic devices. Ungrounded equipment may produce static electricity
which can ignite fuel vapors.
· Work stands shall be equipped with a personnel static discharge plate of copper or zinc.
The plate shall be attached in such a position so that personnel can contact the plate
before coming in contact with the aircraft. High static electrical charges are created by the
contact and separation of unlike substances, or by any sort of motion of persons or
material. These charges are a constant source of danger when generated in the presence
of fuels or flammable vapors.
Fuel tanks shall not be drained near the end of the working day and then allowed to stand
empty overnight. This action could make a perfect set of conditions for producing explosive
vapors. The critical fuel-air ratio could develop a residue fuel drains down the sides of the
tank, forms puddles, and evaporates into the air of the tank.
Drain fuel cells.
The flashpoint of empty fuel cells may be reduced by pouring approximately five gallons of lubricating oil,
MIL-L-6081, grade 1010, into each cell.
A larger amount of flushing oil may be required to flush large fuel cells which are installed in
the aircraft or multiple cells with one fuel opening and interconnecting fuel lines. The
important thing to remember is that the bottom of each fuel cell must be flushed. Reduction
of the flashpoint in purging operations will reduce the amount of lubricating oil necessary
when an assembly line operation is set up.