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newSchoolWorks.com › VoTechWorks › Transportation › Aviation Maintenance › Capstone Project: Integrated Aircraft Maintenance and Documentation › Lesson 3
TRN-AVIA22-06 · Lesson 3 · 168 clock hours · practice

Repair, Corrective Maintenance, and Approved-Data Compliance

Objective. The student will correct all logged discrepancies using FAA-approved repair data and standard practices, applying trade math (torque values, drill sizing, rigging measurements, weight-and-balance adjustments) accurately, and will demonstrate correct use of tools and materials throughout each repair to achieve a return-to-service standard.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a certified examiner or master technician in the trade or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Repair, Corrective Maintenance, and Approved-Data Compliance

Every discrepancy logged during inspection must be corrected using FAA-approved data before the aircraft can be returned to service. Approved data includes the aircraft or engine manufacturer's maintenance manuals, FAA Advisory Circulars such as AC 43.13-1B (Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair), Airworthiness Directives, and Supplemental Type Certificate data sheets. Using unapproved methods or substituting materials not listed in the approved data is an airworthiness violation regardless of how logical the repair appears.

Structural Repair: Sheet Metal and Composite

Sheet-metal repairs follow AC 43.13-1B Chapter 4 when no manufacturer data is more restrictive. The repair must restore original strength without adding excessive weight or creating stress concentrations.

Rivet selection and sizing drives structural integrity. Match the rivet material to the parent metal (for example, 2117-T3 AD rivets for most 2024-T3 aluminum structure). Rivet diameter is typically 3× the thickness of the thickest sheet being joined; the grip length must equal the total stack thickness with a manufactured head of 1.5× rivet diameter and a driven head of 0.5× diameter height. Drill the pilot hole undersized, then use the correct drill size for the rivet diameter: a 3/32-inch (No. 40 drill) rivet uses a 3/32-inch diameter hole within the specified tolerance band. Countersinking depth must not exceed the sheet thickness; if it does, dimpling is required instead.

Apply corrosion-inhibiting compound (such as zinc chromate primer or an approved alternative) between faying surfaces before final assembly to prevent galvanic or crevice corrosion. Wear nitrile gloves and work in a ventilated area; many primers and solvents are skin and respiratory hazards.

Composite repairs follow manufacturer-specific data or FAA AC 43.13-1B Chapter 7. Observe pot life and temperature cure requirements for epoxy systems; expired resin must be discarded. Sand only in a well-ventilated area with appropriate respiratory protection; composite dust is a serious inhalation hazard.

Powerplant and Avionics Troubleshooting

Fault isolation starts at the manufacturer's troubleshooting guide: follow each step in order rather than guessing. Document every measurement and finding on the task card as you go. Skipping steps can lead to replacing the wrong component and missing the root cause.

When replacing components, verify the part number and serial number against the approved parts manual before installation. Torque every fastener to the value specified in the approved data. Use a calibrated torque wrench and apply torque smoothly to the final value rather than exceeding it and backing off. Safety-wire or cotter-pin all fasteners called out by the data. Document the torque value, tool calibration date, and your signature on the task card.

Avionics work introduces electrical hazards. De-energize the bus before disconnecting connectors; use your multimeter to verify zero voltage before touching circuit components. Reconnect and perform a functional ground test per the approved data.

Flight-Control Rigging

Flight-control rigging ensures the control surfaces move through the correct deflection range symmetrically and that cables are tensioned within the manufacturer's published limits. Use a protractor or rigging board to measure surface deflection; cable tension with a calibrated tensiometer. Record every measurement on the task card and compare it to the published tolerance table in the manufacturer's manual. If a measurement is out of limits, adjust turnbuckles or push-pull rods, then re-measure. Never accept a borderline reading; if it is not within limits it must be corrected. After rigging, safety-wire all turnbuckle barrels leaving no more than three threads exposed.

Engine Run-Up

The engine run-up is the final functional check for powerplant repairs. Follow the approved run-up checklist step by step—never improvise the sequence. Position the aircraft into the wind on a clear ramp, chock the wheels, and station a fire extinguisher rated for aviation fuels within reach of the run-up operator. Check for personnel and equipment clear of the propeller arc before engine start.

During run-up, verify oil pressure and temperature reach normal operating ranges, magneto drop is within limits, and carburetor heat or alternate air functions properly. Record all readings. An abnormal reading means the discrepancy is not resolved; shut down and reinvestigate before signing off.

Returning to Service and Signing the Task Card

A return-to-service sign-off is a legal certification that the work was performed in accordance with approved data. Every task card entry must be legible, complete, and accurate: describe the work done, list the approved data reference (manual title, revision, and page), list part numbers of replaced parts, state measured values, and sign and certificate-number your entry. Incomplete or false entries are federal violations. Never sign off work you did not perform or did not personally verify meets the approved data.

Safety Summary

Key terms10

Approved dataFAA-accepted technical references—such as manufacturer manuals, AC 43.13-1B, Airworthiness Directives, or STC data—that legally authorize a specific maintenance method, material, or repair.
AC 43.13-1BFAA Advisory Circular titled Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair; serves as approved data for repairs when no manufacturer data is more restrictive.
Grip lengthThe portion of a rivet shank that passes through the material stack; it must equal the total thickness of all sheets being joined so the driven head forms correctly.
Corrosion-inhibiting compoundA primer or sealant applied between faying surfaces during assembly to prevent moisture intrusion and galvanic or crevice corrosion.
Calibrated torque wrenchA torque wrench whose accuracy has been verified against a traceable standard within the required calibration interval; use of an out-of-calibration tool makes the torque value unverifiable.
TensiometerA calibrated tool used to measure cable tension; the reading must be compared to the manufacturer's published tension table corrected for ambient temperature.
Fault isolationA systematic, step-by-step process using the manufacturer's troubleshooting guide to identify the root cause of a discrepancy before replacing any component.
Return-to-service (RTS) sign-offThe mechanic's legal certification, recorded on the maintenance record and task card, that the work was completed in accordance with approved data and the aircraft is airworthy.
Faying surfaceThe mating interface between two structural members that are fastened together; corrosion protection is applied here before final assembly.
CountersinkingCutting a conical recess in the top sheet so a flush rivet head sits level with the surface; allowable only when the sheet is thick enough that the countersink does not extend beyond the sheet.

Worked examples4

1. A repair requires MS20470AD4 rivets (3/32-inch diameter, 2117-T3 material) through a two-sheet stack. Sheet 1 is 0.040 inch thick; Sheet 2 is 0.032 inch thick. What is the correct grip length range, and what is the minimum acceptable driven-head diameter?
  1. Calculate total stack thickness: 0.040 + 0.032 = 0.072 inch. The grip length must equal the stack thickness, so the grip length needed is 0.072 inch.
  2. MS20470 rivets are available in 1/16-inch (0.0625 in) grip increments. Select the grip length equal to or just above 0.072 inch. The standard grip increment above 0.0625 inch is 3/32 inch (0.09375 in), so the correct grip length is 3/32 inch (grip code -3 in rivet part number notation, meaning 3 sixteenths — verify against the applicable rivet table).
  3. Calculate minimum driven-head diameter: per AC 43.13-1B, the driven head diameter must be at least 1.5× the rivet shank diameter. Rivet diameter = 3/32 inch = 0.09375 inch. Minimum driven head diameter = 1.5 × 0.09375 = 0.140625 inch, which rounds to approximately 0.141 inch.
  4. Calculate minimum driven-head height: minimum height = 0.5× rivet diameter = 0.5 × 0.09375 = 0.047 inch.
Answer: Grip length: 3/32 inch (select the next standard grip above the 0.072-inch stack). Minimum driven-head diameter: approximately 0.141 inch. Minimum driven-head height: approximately 0.047 inch.
2. During flight-control rigging you measure 2-inch cable tension on an aileron cable. The manufacturer's table specifies 30–40 lb at 70 °F. You turn the turnbuckle barrel 8 full turns on one side, adding approximately 3 lb per full turn. What is the approximate resulting tension, and is it within limits?
  1. Identify starting tension: 2 lb (far below the 30–40 lb specification).
  2. Calculate tension added: 8 turns × 3 lb/turn = 24 lb added.
  3. Calculate new tension: 2 + 24 = 26 lb.
  4. Compare to limits: 26 lb is below the lower limit of 30 lb, so the cable is still out of tolerance. Additional adjustment is required. Continue adjusting and re-measuring until the reading falls between 30 and 40 lb.
Answer: Approximate resulting tension is 26 lb, which is still below the 30-lb lower limit. Further adjustment is needed before this cable is within specification.
3. A torque specification calls for 150 in-lb on a bolt, but you must use a 6-inch extension on your torque wrench. The torque wrench handle length (pivot to drive) is 12 inches. What value should you set on the torque wrench dial to achieve 150 in-lb at the fastener?
  1. Identify the correction formula for a rigid inline extension: Tw = (Tf × L) ÷ (L + E), where Tw = torque wrench setting, Tf = desired torque at fastener, L = effective wrench length, E = extension length.
  2. Substitute values: Tw = (150 × 12) ÷ (12 + 6) = 1800 ÷ 18 = 100 in-lb.
  3. Set the torque wrench to 100 in-lb. When the wrench clicks at 100 in-lb, the actual torque delivered to the fastener will be 150 in-lb.
Answer: Set the torque wrench to 100 in-lb to deliver 150 in-lb at the fastener when using a 6-inch rigid inline extension on a 12-inch wrench.
4. A No. 30 drill is specified to drill rivet holes for 1/8-inch (0.125-inch) rivets. A No. 30 drill has a diameter of 0.1285 inch. What is the clearance between the hole and the rivet, and is this within the typical AC 43.13-1B tolerance of +0.003 / −0.000 inch over nominal rivet diameter?
  1. Nominal rivet diameter: 0.125 inch.
  2. Drill diameter (hole size): 0.1285 inch.
  3. Clearance: 0.1285 − 0.125 = 0.0035 inch.
  4. Compare to tolerance: AC 43.13-1B permits a hole up to 0.003 inch over the nominal rivet diameter, meaning the maximum acceptable hole is 0.125 + 0.003 = 0.128 inch. The 0.1285-inch hole exceeds this by 0.0005 inch and is technically out of the tolerance band.
Answer: Clearance is 0.0035 inch, which exceeds the +0.003 inch maximum allowance. Verify against the specific approved data table; if out of tolerance, the next acceptable repair option (such as the next larger rivet size) must be selected and documented.

The math in this lesson2

Learners multiply rivet diameter by 1.5 and 0.5 to find minimum driven-head diameter and height.
6.RP.3N-Q.3
Brush up in the math halls at newSchoolWorks.com:
In class: Perform sheet-metal or composite structural repair (as applicable to the assigned aircraft) following AC 43.13-1B repair data or manufacturer-approved data, selecting correct rivet type and size using trade math, drilling and countersinking to specified tolerances, and applying corrosion-inhibiting compound per the approved process. · Troubleshoot and correct the two assigned powerplant or avionics system discrepancies using the manufacturer's troubleshooting guide and fault-isolation procedures; replace or adjust components as directed by the approved data, torquing all fasteners to specification using calibrated torque wrenches and documenting each step on the task card. · Perform a return-to-service functional test for each corrected system—including a flight-control rigging check with measurements recorded against published tolerances and an engine run-up following the checklist—and confirm that all discrepancies are resolved and all measurements are within limits before signing off the task card.
Materials: Sheet-metal or composite repair materials (aluminum sheet, rivets, epoxy/fabric as applicable); calibrated drill press and hand drills; rivet gun and bucking bars; calibrated torque wrenches; safety wire and pliers; turnbuckles and rigging tools; engine run-up checklist; multimeter; required replacement parts (per approved parts manual); AC 43.13-1B; manufacturer repair manual; task cards; required PPE including fire extinguisher at run-up area
Check: Instructor inspects each completed repair using the same measurement tools against published limits; torque values are spot-checked with a calibrated torque wrench; a pass requires all repairs within tolerances specified in approved data, all task cards signed with accurate entries, and no unsafe conditions present—any out-of-tolerance repair is rejected and must be redone before portfolio assembly.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

General – Maintenance Forms and Records / Regulations
1. When no manufacturer's structural repair manual exists for a particular repair, a mechanic may use which source as approved data for sheet-metal repairs on a certificated aircraft?
Airframe – Structures / Sheet Metal
2. A countersink is being cut for a flush rivet in a thin aluminum skin. Inspection reveals the countersink depth equals the full sheet thickness. What is the correct action?
Powerplant – Engine Ignition and Electrical Systems
3. During an engine run-up following a magneto replacement, the left-magneto check shows an RPM drop exceeding the manufacturer's published limit. What is the correct next step?
Airframe – Structures / Sheet Metal
4. Which rivet material is typically used to join 2024-T3 aluminum structure in general aviation repairs?
General – Tools / Trade Mathematics
5. A torque wrench setting must be corrected when using a rigid inline extension. If the desired fastener torque is 120 in-lb, the wrench effective length is 10 inches, and the extension length is 5 inches, what is the correct torque wrench dial setting?
Airframe – Electrical Systems / General Safety
6. Before disconnecting an avionics circuit connector for component replacement, what is the most important immediate safety step?
General – Maintenance Forms and Records / Regulations
7. What information is required in a maintenance record entry when signing off a completed repair to return an aircraft to service?
Airframe – Structures / Flight Controls
8. After completing a flight-control cable rigging adjustment, how must turnbuckle barrels be safetied, and what is the maximum number of exposed threads allowed per barrel?
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