Corrosion Identification on the A&P Oral: AM.I.G.K6 Explained

October 26, 2026 · Primary sources checked October 26, 2026

Corrosion identification on the airframe and powerplant (A&P) oral means recognizing and inspecting corrosion: the Federal Aviation Administration (FAA) Airman Certification Standards (ACS) element AM.I.G.K6 is “Corrosion identification and inspection.” For oral and practical (O&P) preparation, explain the visible clue, where the handbook places that form, and what the appearance cannot tell you about hidden damage.

FAA-S-ACS-1 (November 1, 2021) — printed 11, PDF 16; General Subject G

On this page

What does AM.I.G.K6 cover?
Which corrosion clues should you distinguish for the O&P?
Keep the source qualifications with the clue
What does a corrosion inspection require?
What does the FAA missed-code data show for AM.I.G.K6?
Practice the spoken part
Before the oral

What does AM.I.G.K6 cover?

The next element, AM.I.G.K7, is “Corrosion removal and treatment procedures.” Keep identification separate from choosing a removal method. The cues below come from FAA-H-8083-30B, Chapter 8, and Advisory Circular (AC) 43.13-1B, Chapter 6; the linked treatment guides cover that later step.

FAA-S-ACS-1 (November 1, 2021) — printed 11, PDF 16; General Subject G

Which corrosion clues should you distinguish for the O&P?

Surface corrosion: look for general roughening, etching, or pitting on a metal surface; powdery corrosion products frequently accompany the damage.
Corrosion beneath a coating may instead lift paint or plating into small blisters.
AC 43.13-1B says that on a polished surface, general surface corrosion is first seen as a general dulling of the surface and, if allowed to continue, the surface becomes rough and possibly frosted; discoloration or general dulling of metal created by exposure to elevated temperatures is not to be considered general surface corrosion.
Pitting: the handbook calls it one of the most destructive and intense forms of corrosion; it can occur in any metal but is most common on metals that form protective oxide films, such as aluminum and magnesium alloys; it is first noticeable as a white or gray powdery deposit, similar to dust, and tiny holes or pits can be seen when the deposit is cleaned away.
Tiny pit openings may penetrate deeply into structural members; surface appearance can seriously understate the damage.
Filiform corrosion: the identifying cue is a worm-like trace beneath an organic paint coating.
The handbook says that if filiform corrosion is not removed, the area treated, and a protective finish applied, it can lead to intergranular corrosion, especially around fasteners and at seams.
Concentration-cell or crevice corrosion: the handbook describes corrosion in a metal-to-metal joint, at the edge of a joint even when the joined metals are identical, or on a spot covered by a foreign material.
Metal-ion concentration cells: under faying surfaces and near a crevice, the metal exposed to the lower metal-ion concentration is the area that corrodes.
Oxygen concentration cells: examples include areas under gaskets, wood, rubber, or other materials contacting metal; the low-oxygen area corrodes.
Active-passive cells: dirt can break the passive film locally, exposing active metal and producing rapid pitting beside a larger protected surface.
Intergranular corrosion: the attack follows alloy grain boundaries; aluminum alloys and some stainless steels are particularly susceptible.
Intergranular corrosion may exist without visible surface evidence.
Exfoliation: an advanced form of intergranular corrosion lifts surface grains; extruded sections such as spars are examples of susceptible locations.
The handbook calls exfoliation visible evidence of intergranular corrosion, but says it is difficult to detect in its initial stage.
Galvanic corrosion: dissimilar metals contact one another in an electrolyte; a buildup of corrosion at their joint is a usual recognition cue.
The handbook warns that dissimilar-metal attack can be very serious because, in many instances, it takes place out of sight, and the only way to detect it before structural failure is by disassembly and inspection.
Stress-corrosion cracking: constant or cyclic stress acts with a damaging chemical environment; stress may be internal or externally introduced.
Stress corrosion is difficult to recognize before it has overcome the design safety factor.
The handbook says stresses near the yield strength are generally necessary to promote stress-corrosion cracking; however, failures may occur at lower stresses.
Fatigue corrosion: cyclic stress and a corrosive environment act together; AC 43.13-1B warns that failure then occurs at stress levels that can be dangerously low, depending on the number of cycles assigned to the life-limited part, and the crack often grows from a corrosion pit or pits.
In the first stage of fatigue corrosion failure, AC 43.13-1B says the combined action of corrosion and cyclic stress damages the metal by pitting and crack formations to such a degree that fracture by cyclic stress will occur, even if the corrosive environment is completely removed.
Fretting: slight relative motion between normally stationary mating surfaces produces pitting and finely divided debris.
A smoking rivet on engine cowling or wing skin is the handbook’s common fretting example; a black ring identifies that smoking-rivet cue.

Keep the source qualifications with the clue

The fretting paragraph says water vapor greatly increases deterioration. The same paragraph also says the reaction is not driven by an electrolyte and moisture may inhibit it. The source gives both statements; do not turn the moisture wording into a universal diagnostic rule.

FAA-H-8083-30B, General (2023) — printed 8-9, PDF 333

The General handbook allows direct chemical or electrochemical attack for surface corrosion. AC 43.13-1B describes general surface corrosion as direct chemical attack. Preserve that wording difference rather than inventing a single mechanism from appearance alone.

FAA-H-8083-30B, General (2023) — printed 8-5, PDF 329 · AC 43.13-1B, Change 1 — printed 6-5, PDF 276; 6-12

What does a corrosion inspection require?

Paint can mask the initial stages of corrosion; because corrosion products occupy more volume than the original metal, the handbook says painted surfaces must be inspected often for irregularities such as blisters, flakes, chips, and lumps. The handbook starts corrosion inspection with thorough cleaning, followed by a general visual inspection and a detailed inspection of damage or suspect areas. The handbook says adequate access for inspection must be obtained by removing access panels and adjacent equipment, cleaning the area as necessary, and removing loose or cracked sealants and paints.

FAA-H-8083-30B, General (2023) — printed 8-3, PDF 327 · FAA-H-8083-30B, General (2023) — printed 8-11, PDF 335

Nondestructive inspection (NDI) methods have limitations and must be performed only by qualified and certified NDI personnel. Eddy-current, X-ray, and ultrasonic methods require equipment calibrated each time it is used and a controlling reference standard for reliable results. During corrosion-control maintenance, consult the Safety Data Sheet (SDS) for chemicals used. Do not transfer metal contamination by reusing an abrasive pad on a different metal; the handbook also warns that improper use of steel cleaning products, such as steel wool or a steel wire brush, on aluminum or magnesium can force small pieces of steel into the metal, causing corrosion and ruining the adjoining surface.

FAA-H-8083-30B, General (2023) — printed 8-11, PDF 335 · FAA-H-8083-30B, General (2023) — printed 8-10, PDF 334 · FAA-H-8083-30B, General (2023) — printed 8-6, PDF 330

AC 43.13-1B contains methods, techniques, and practices acceptable to the Administrator for the inspection and repair of nonpressurized areas of civil aircraft, only when there are no manufacturer repair or maintenance instructions; its data generally pertains to minor repairs. The AC says its repair data may also be used as approved data when the user has determined that it is appropriate to the product being repaired, it is directly applicable to the repair being made, and it is not contrary to manufacturer’s data. Our advice: use this guide to rehearse recognition, not to authorize chemical treatment, disassembly, or a return-to-service decision.

AC 43.13-1B, Change 1 — printed unnumbered cover, PDF 1; Purpose · AC 43.13-1B, Change 1 — printed unnumbered cover, PDF 1; Purpose a–c

What does the FAA missed-code data show for AM.I.G.K6?

Frequently Missed Knowledge Test ACS Codes — 2nd Quarter, CY24: the report period is July 1, 2023, through June 30, 2024; the Aviation Maintenance Technician General (AMG) row for AM.I.G.K6 shows “Percent Missed” 77.32%.

Frequently Missed Knowledge Test ACS Codes — 2nd Quarter, CY24 — printed 1 of 1, PDF 1; AMG, AM.I.G.K6 row

Frequently Missed Knowledge Test ACS Codes — 3rd Quarter, CY24: the report period is October 1, 2023, through September 30, 2024; the AMG row for AM.I.G.K6 shows “Percent Missed” 77.29%.

Frequently Missed Knowledge Test ACS Codes — 3rd Quarter, CY24 — printed unnumbered single page, PDF 1; AMG, AM.I.G.K6 row

Frequently Missed Knowledge Test ACS Codes — 4th Quarter, CY24: the report period is January 1, 2024, through December 31, 2024; the AMG row for AM.I.G.K6 shows “Percent Missed” 77.12%.

Frequently Missed Knowledge Test ACS Codes — 4th Quarter, CY24 — printed unnumbered single page, PDF 1; AMG, AM.I.G.K6 row

Frequently Missed Knowledge Test ACS Codes — 1st Quarter, CY25: the report period is April 1, 2024, through March 31, 2025; the AMG row for AM.I.G.K6 shows “Percent Missed” 77.45%.

Frequently Missed Knowledge Test ACS Codes — 1st Quarter, CY25 — printed unnumbered single page, PDF 1; AMG, AM.I.G.K6 row

Frequently Missed Knowledge Test ACS Codes — 2nd Quarter, CY25: the report period is July 1, 2024, through June 30, 2025; the AMG row for AM.I.G.K6 shows “Percent Missed” 78.49%.

Frequently Missed Knowledge Test ACS Codes — 2nd Quarter, CY25 — printed unnumbered single page, PDF 1; AMG, AM.I.G.K6 row

The 2nd Quarter, CY24 report’s footnote narrows its Airframe (AMA) and General (AMG) statistics to July 31, 2023, through June 30, 2024. The five figures above are the FAA reports’ code-specific “Percent Missed” figures, not exam failure rates or a prediction of your result. The overlapping reporting windows are not independent quarterly cohorts.

Frequently Missed Knowledge Test ACS Codes — 2nd Quarter, CY24 — printed 1 of 1, PDF 1; AMA/AMG footnote

Read the FAA missed-code context

See AM.I.G.K6

Practice the spoken part

DMEReady is an artificial intelligence (AI) voice examiner for the A&P oral, not a human designated mechanic examiner (DME), a written-test question bank, or hands-on practical training. You answer out loud in your phone or computer browser; the first drill is free with no sign-up, and the session report identifies what you covered, what you missed, what a complete answer includes, and where to read in the FAA handbooks. DMEReady is independent and is not affiliated with or endorsed by the FAA.

Frequently asked questions

Does a clean-looking surface rule out corrosion on the O&P?

No. The General handbook says intergranular corrosion may exist without visible surface evidence. The handbook also says paint can mask the initial stages of corrosion.

FAA-H-8083-30B, General (2023) — printed 8-7, PDF 331 · FAA-H-8083-30B, General (2023) — printed 8-3, PDF 327

Are tiny visible pits necessarily shallow?

No. The handbook says small pit openings may penetrate deeply into structural members and cause damage completely out of proportion to their surface appearance.

FAA-H-8083-30B, General (2023) — printed 8-6, PDF 330

Is every dull area general surface corrosion?

No. AC 43.13-1B says dulling or discoloration of metal from exposure to elevated temperatures is not to be considered general surface corrosion, although general surface corrosion on a polished surface is first seen as a general dulling.

AC 43.13-1B, Change 1 — printed 6-5, PDF 276; 6-12

Does the FAA missed percentage predict my outcome?

No. Each FAA Frequently Missed Knowledge Test ACS Codes report gives a code-specific “Percent Missed” figure for its own reporting period; the figure does not predict an individual exam result.

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Passed a written? Get your oral study plan by email

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Related guides

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Primary sources

Before the oral

Under the FAA Mechanic Test Generator (MTG) FAQ, each distinct missed code among the ACS codes on your Airman Knowledge Test Report (AKTR) adds one oral question, plus at least four randomly generated questions per applicable section. Several missed written questions under one code add only one additional oral question. Our advice: explain the topic with the source closed, then reopen the exact page to check the conditions and cautions you left out.

Mechanic Test Generator FAQs (May 22, 2023) — printed unnumbered, PDF 3; Oral-related Questions · Mechanic Test Generator FAQs (May 22, 2023) — printed unnumbered, PDF 4; Oral-related Questions (continued)

Practice explaining it out loud

About this guide: drafted with AI from the FAA sources listed on this page and checked claim by claim against them. Not reviewed by an A&P mechanic or DME. How we make our guides

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