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Corrosion cause at piano-type hinges

Aviation Mechanic General (AMG) practice question 30 of 36 on Cleaning and Corrosion Control. ACS element AM.I.G.K4 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONA mechanic finds corrosion inside a piano-type hinge on an aluminum access panel. What is the principal cause of corrosion at this location?

  1. AContact between the steel pin and the aluminum hinge
  2. BFretting of the hinge leaves during normal actuation cycles
  3. CAlkaline cleaner trapped in the panel lap joint
Show the answer and explanation

Correct answer: A. Contact between the steel pin and the aluminum hinge

  • A — correct Piano-type hinges are prime corrosion spots because of the dissimilar metal contact between the steel hinge pin and the aluminum hinge.
  • B — incorrect Fretting corrosion occurs between mating surfaces normally at rest that are subjected to slight relative motion, and its common example is the smoking rivet on cowling and wing skins.
  • C — incorrect An alkaline cleaner that is not rinsed can corrode lap joints of riveted or spot-welded sheet metal, but that is a different location and mechanism.

BACKGROUND

Piano-type hinges are prime spots for corrosion because of the dissimilar metal contact between the steel pin and the aluminum hinge. They are also natural traps for dirt, salt, and moisture, which supply the electrolyte the galvanic cell needs. Hidden corrosion forms inside the hinge, and the joint can freeze so that lugs break off when the hinge is actuated. Inspection of hinges must therefore include lubrication and actuation through several cycles to ensure complete lubricant penetration. Water-displacing lubricants are used when servicing piano hinges.

STUDY TIP

When a question names a joint made of two different metals, look first for galvanic (dissimilar metal) attack, and remember that piano hinges are inspected by actuating them after lubrication.

KEY POINTS

  • Piano hinges pair a steel pin with an aluminum hinge, creating dissimilar metal contact.
  • They also trap dirt, salt, and moisture, supplying the electrolyte.
  • Service them with water-displacing lubricants and actuate through several cycles.

SOURCES

  • FAA-H-8083-30B ch08 "External Skin Areas"
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MORE ON CLEANING AND CORROSION CONTROL

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.