7-3
7.1.5.6 When mercury spills occur in a lower cargo compartment, use a portable x ray machine, if available, along the outside lower surface of the fuselage to check suspected hidden corrosion areas between the skin, stringers, and frames below the floor. Droplets of mercury will show on an x ray image as small, white spots. Corrosion and embrittlement will appear as tree-like forms completely penetrating a structural component.
7.1.5.7 Inspect bronze/brass control cable turnbuckle barrels for mercury discoloration. Replace if the slightest discoloration is detected.
7.1.6 Removal procedure and precautions necessary when mercury is spilled are:
WARNING: Vacuum air passing over the mercury deposited in the glass container picks up mercury vapors and exhausts them from the vacuum cleaner.
Avoid breathing mercury vapors.
CAUTION: An air hose should not be used to dislodge mercury from aircraft under any circumstances.
7.1.6.1 Use a high-capacity vacuum cleaner with a trap-type glass container attached to the large vacuum hose. The size of the pickup hose from the container should be about 1/4 inch in diameter to increase the amount of suction applied to the mercury. Due to the weight of mercury, the container will catch the mercury before it can enter the vacuum cleaner hose.
7.1.6.2 An all-rubber storage battery water syringe, or a medicine dropper, may be used to remove mercury if the trap-type glass container and vacuum cleaner are not available. Cellulose tape may be used to pick up very tiny particles of mercury.
7.1.6.3 General cleanup and inspection, using the equipment available, should be made immediately after spillage occurs or is detected.
7.2 Corrosion Protection for Agricultural Aircraft.
7.2.1 G eneral . Practically all chemicals used in dusting and spraying operations are corrosive by nature and hasten deterioration of fabric, metal, and wood. It is essential to safe operation that precautions be taken to prevent corrosion and deterioration of wood, metal, and fabric. Cleanliness of the airplane is one of the most important precautions of all. If it were practicable and feasible to clean the airplane thoroughly, that is, give it a thorough dry washing inside and out after each day’s work, probably no special corrosive preventive measures would be necessary.
7.2.2 Precautions. Since thorough daily cleaning is not practicable, take the following precautions:
7.2.2.1 A ll fittings and metal structures should be covered with two coats of epoxy primer, a heavy preservative, conforming to MIL-SPEC MIL-C-16173,
7-4 Corrosion Preventive Compound, Solvent Cutback, Cold-Application, Grade 2 (paralketone), or equivalent material. This coating should be applied to items such as wing-root fittings, wing-strut fittings, control-surface hinges, horns, or mating edges of fittings and attach bolts.
7.2.2.2 Non-stainless steel control cables should be coated with paralketone or equivalent protective coating, or should be replaced with corrosion-resistant cables.
7.2.2.3 Periodic inspection of all critical portions of the aircraft structure should be made. Structural parts showing corrosion should be cleaned and refinished if the corrosion attack is superficial. If the part is severely corroded, it should be replaced.
7.2.2.4 Experience has shown that additional access openings, enabling ready inspection of lower and rearward portions of the fuselage, are particularly desirable.
7.2.2.5 Provide additional drainage and ventilation for all interiors to prevent collection of moisture.
7.2.2.6 At the time of recovering, both metal and wood airplane structural members should be coated with two coats of epoxy primer, followed by dope-proof paint or wrapping with cellophane tape.
7.2.2.7 Spray interiors of metal-covered wings and fuselages with an adherent corrosion inhibitor.
7.2.2.8 Wash exterior surfaces with clear fresh water at least once a week. Interior surfaces should also be washed, taking care to prevent damage to electrical circuits or other items subject to malfunctioning due to moisture.
7.2.2.9 Opening in the wings, fuselage, and control-surface members, such as tail-wheel wells or openings for control cables, should be sealed as completely as possible to prevent entry of dust or spray.
7.3–7.99. RESERVED.
Advisory Circular Feedback Form If you find an error in this AC, have recommendations for improving it, or have suggestions for new items/subjects to be added, you may let us know by contacting the Flight Standards Directives Management Officer at 9-AWA-AFB-120-Directives@faa.gov.
Subject: AC 43-4B, Corrosion Control for Aircraft Date: _____________________ Please check all appropriate line items:
An e rror ( proc edural or typographical) has been noted in paragraph ____________ on page _______.
Recommend paragraph _____________ on page __________ be changed as follows:
______________________________________________________________________ ______________________________________________________________________ In a future change to this AC, please cover the following subject:
(Briefly describe what you want added.)
______________________________________________________________________ ______________________________________________________________________ Other comments:
______________________________________________________________________ ______________________________________________________________________ I would like to discuss the above. Please contact me.
Submitted by: Date: ______________________