Cleaning and Corrosion Control

Study Materials

AMT-G, FAA-H-8083-30, AC 43.13-1

Typical Oral Questions

  1. Identify the areas of an aircraft that are most prone to corrosion.

    Battery compartment, exhaust system and exhaust trails, wheel wells, lower area of the belly (bilge), piano hinges, areas of dissimilar metal contact, welded areas, inside of fuel tanks especially integral tanks, metal fittings and under high stress, lavatories and foodservice areas.

  2. Where is filiform corrosion most likely to occur on an aircraft?

    Under a dense coating of topcoat enamel such as polyurethane. Filiform corrosion is caused by improperly cured primer.

  3. Where is fretting corrosion most likely to occur on an aircraft?

    In a location where there is a slight amount of relative movement between two components, and no way for the corrosive residue to be removed as it forms.

  4. Where is intergranular corrosion most likely to occur on an aircraft?

    Along the grain boundaries of aluminum alloys that have been improperly heat-treated. Extruded aluminum alloy is susceptible to intergranular corrosion.

  5. Where is dissimilar metal corrosion most likely to occur on an aircraft?

    Anywhere different types of metal come in contact with each other, especially where moisture is present.

  6. Where is stress corrosion most likely to occur on an aircraft?

    In any metal component that is continually under a tensile stress. The metal around holes in castings that are fitted with pressed-in bushings are susceptible to stress corrosion.

  7. What must be done to a piece of aluminum alloy to remove surface corrosion and to treat the metal to prevent further corrosion?

    Remove the corrosion residue with a bristle brush or a nylon scrubber. Neutralize the surface with chromic acid or with some type of conversion coating. Protect the surface from further corrosion with a coat of paint.

  8. What is used to keep corrosion from forming on structural aluminum alloy?

    An oxide coating or aluminum cladding.

  9. How may rust be removed from a highly stressed metal part?

    By glass bead blasting, by careful polishing with mild abrasive paper or by using fine buffing compound on a cloth buffing wheel.

  10. How should corrosion be minimized at piano hinges?

    They should be kept as clean and dry as practicable and lubricated with a low viscosity moisture dispersing agent.

  11. What tools are proper for removing corrosion from aluminum alloy?

    Aluminum wool or aluminum wire brushes. Severe corrosion can be removed with a rotary file.

  12. What is used to clean transparent plastic windshields and windows of an aircraft?

    Mild soap and plenty of clean water.

  13. What is used to neutralize the electrolyte from a lead-acid battery that has been spilled on an aircraft structure?

    A solution of bicarbonate of soda and water.

  14. What is used to neutralize the electrolyte from a nickel-cadmium battery that has been spilled on an aircraft structure?

    A solution of boric acid and water, or vinegar.

  15. What solvent is recommended for removing grease from aircraft fabric prior to doping it?

    Methyl Ethyl Ketone (MEK) or lacquer thinner.

  16. What can be used to repair the anodized surface of an aluminum alloy part?

    A chemical conversion coating such as Alodine® (also known as Bonderite®).

  17. What type of device is used to remove surface corrosion from a piece of magnesium alloy?

    A stiff hog-bristle brush.

  18. How is the inside of structural steel tubing protected from corrosion?

    The tubing is filled with hot linseed oil and then drained.

  19. Why are some portions of the structure of an aircraft dope proofed before they are covered with fabric?

    Dope proofing keeps the fabric from sticking to the structure when the first coat of dope is applied. The fabric normally sags enough to touch the structure before it begins to pull taut.

  20. What is done to cotton and linen fabric to protect it from mildew?

    The first coat of dope that is used on cotton and linen fabric has a mildewcide mixed in it.

  21. How is polyester synthetic fabric shrunk on an aircraft structure?

    It is shrunk with heat from an iron or from a heated blower.

  22. Why should wooden wing spars be finished with a transparent varnish?

    The transparent finish allows any decay or rot that develops in the wood to be detected.

  23. What is used as a protective finish for the inside of steel tubing?

    Hot linseed oil.

  24. What happens to an enamel finish when paint remover is applied to it?

    The enamel softens and swells so that it pulls away from the surface of the metal.

  25. What should be done to an aircraft surface that is covered with paint remover to give the remover the maximum amount of time to soak into the old finish?

    The surface should be covered with a piece of polyethylene sheeting such as a paint drop cloth. This will keep the solvents from evaporating before they have time to penetrate the paint film.

  26. When mixing epoxy paint, should the converter be added to the resin or the resin to the converter?

    The converter should always be added to the resin, never the resin to the converter.

  27. What is the general reason for runs and sags in a finish that is being sprayed onto a flat surface?

    Too much paint is being applied. The film is too thick.

  28. What can be done to remedy blushing that has formed on a doped surface that has just been sprayed?

    Spray a very light mist coat of a mixture of one part retarder to two parts of thinner over the blushed area. Allow it to dry and spray on another coat. If this does not remove the blush, the blushed dope will have to be sanded off and new dope applied.

  29. What safety precaution must be observed when sweeping a paint room that has dried dope or lacquer overspray on the floor?

    The floor must be wet down with water before it is swept. Static electricity from dry sweeping can cause a fire.

  30. What will happen if dope is sprayed over an enameled surface?

    The thinner in the dope will penetrate the enamel surface and cause it to swell.

  31. What are three types of primer that may be used when painting an aircraft?

    Zinc chromate primer, wash primer, and epoxy primer.

  32. How is the finish removed from a fiberglass aircraft component that is being repaired?

    The finish must be sanded off. Paint remover can soften the resin of which the component is made.

  33. What are the two basic types of dope that are used on fabric-covered aircraft?

    Nitrate dope and butyrate (CAB) dope.

  34. What kind of dope is used on polyester synthetic fabric that has been heat-shrunk on an aircraft structure?

    Nontautening butyrate dope.

Typical Practical Projects

  1. Given samples of corroded aircraft structural materials, identify the type of corrosion and describe the correct procedure for removing the corrosion and treating the damaged area to prevent further corrosion.
  2. Remove the corrosion from a piece of aluminum alloy furnished by the examiner and treat the metal to prevent further corrosion.
  3. Treat a piece of aircraft structure so moisture cannot reach the metal and cause corrosion.
  4. Select the proper cleaning materials and remove grease and exhaust deposits from an aircraft structure.
  5. Select the proper cleaning materials and remove oil that has been spilled on an aircraft tire.
  6. Demonstrate to the examiner the correct way to remove rust from a highly stressed engine component.
  7. Properly remove the finish from a piece of painted aluminum alloy.
  8. Properly remove the finish from a piece of painted fiberglass reinforced plastic material.
  9. Demonstrate the correct way to clean a transparent plastic flight deck enclosure or windshield.
  10. Remove corrosion from a lead-acid battery box and treat the box to prevent further corrosion.
  11. Treat the cylinders of a reciprocating engine to prevent rust and corrosion when the engine is being prepared for long-term storage.
  12. Treat a piece of welded steel tubular structure to prevent rust and corrosion inside the tubing.
  13. Mix dope and the correct thinner to get the proper viscosity for spraying. Demonstrate to the examiner the correct way to spray the dope on an aircraft surface.
  14. Determine whether the dope that is on a piece of fabric-covered structure is nitrate or butyrate.
  15. Demonstrate to the examiner the correct way of applying the first coat of dope to the fabric that is being installed on an aircraft structure.
  16. Demonstrate to the examiner the correct way of dry sanding a fabric-covered aircraft wing.
  17. Demonstrate to the examiner the correct way to spray a surface with a polyurethane enamel.
  18. Identify the correct thinner to use with a list of finishing materials that is furnished by the examiner.
  19. Properly adjust the pressure of the air on a spray gun and pressure pot for spraying aircraft dope.
  20. Explain to the examiner the correct size and location for the identification numbers that are required on an aircraft.
  21. Properly remove the finish from a piece of fiberglass-reinforced aircraft structure so the structure can be repaired.
  22. Explain to the examiner the reason for using aluminum-pigmented dope on a fabric-covered aircraft structure. Explain why it is important to not use too much aluminum dope.

[10-2024]