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newSchoolWorks.com › VoTechWorks › Transportation › Aviation Maintenance › Capstone Project: Integrated Aircraft Maintenance and Documentation › Lesson 2
TRN-AVIA22-06 · Lesson 2 · 120 clock hours · lab

Multi-System Inspection and Discrepancy Identification

Objective. Using only FAA-approved data, the student will perform a structured inspection of assigned airframe, powerplant, and avionics systems, identify all discrepancies against serviceable limits, and record each finding on a standardized discrepancy log with sufficient detail to support a maintenance decision.

⚠ 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.

Multi-System Inspection and Discrepancy Identification

A structured, multi-system inspection is the foundation of every major maintenance event. In a capstone project context, you are expected to bring together everything you have learned—airframe, powerplant, and avionics—and apply it simultaneously to a real aircraft or assembly. The goal is not simply to find problems; it is to find every problem, measure it accurately, and document it so that any qualified mechanic could pick up your discrepancy log and make a sound maintenance decision.

Why Authorized Data Governs Everything

FAA regulations require that maintenance be performed in accordance with FAA-approved data. For any specific aircraft this means the Aircraft Maintenance Manual (AMM), the Type Certificate Data Sheet (TCDS), engine and propeller overhaul manuals, and applicable Airworthiness Directives (ADs). You may not substitute memory, internet sources, or manufacturer marketing material for these references. Before you measure a single dimension, identify the correct manual, the correct revision, and the correct section for the component you are inspecting. Write the manual reference on your discrepancy log next to every finding.

Systematic Inspection Sequence

Random inspection misses items. A disciplined sequence—zone by zone, system by system—ensures complete coverage. A common professional approach follows the aircraft's own maintenance manual inspection checklist in order:

1. Airframe and flight controls – Inspect primary structure for cracks, corrosion, and deformation. Check flight control rigging by measuring control surface travel with a protractor or rigging board and comparing to AMM limits. Inspect landing gear for proper extension, tire condition, brake wear, and torque link security. Record every measured value, not just pass/fail.

2. Powerplant and engine mount – Perform a differential compression check on each cylinder. Inspect the oil system for leaks, sludge, and proper quantity. Check ignition system continuity and inspect leads for chafing and security. Examine the engine mount for cracks and loose hardware. Compare all findings to the TCDS and engine overhaul manual limits.

3. Avionics and electrical wiring – Inspect wiring bundles for chafing, broken insulation, and corrosion at connectors. Verify antenna mounting hardware is secure. Use a calibrated multimeter to check continuity of critical circuits and insulation resistance where access allows. Log each discrepant wire by its identification number and physical location.

Performing and Recording Measurements

A discrepancy log entry is only useful if it contains measured values. "Oil leak noted" is not a discrepancy log entry; "oil seepage at the left magneto P-lead grommet, approximately 1 inch diameter stain on induction housing, AMM Section 72 limit is no active leakage" is. For every finding record:

For the compression check, record cylinder number, differential pressure (in psi), and the pressure supply used. The engine overhaul manual specifies the minimum acceptable differential reading for that engine model. A cylinder that leaks down excessively must be investigated further—the bore scope is your next tool. Insert it through the spark plug hole, rotate the propeller slowly, and inspect the cylinder walls and piston crown for scoring, cracks, or broken rings.

Safety Requirements for This Lab

PPE is mandatory throughout. Wear safety glasses at minimum; add hearing protection during any operational run-up. Inspect the area around the propeller arc before any ignition system check—treat every magneto as live until the ignition switch is verified OFF and the propeller is physically secured.

Apply lockout/tagout (LOTO) procedures before working on any electrical system. De-energize the aircraft bus, pull and tag the master switch, and verify with a multimeter that the circuit is de-energized before touching wiring. Never assume a circuit is safe because the switch is off.

When using the compression tester, ensure the piston is at top dead center on the compression stroke before applying air pressure. An unexpected piston movement can rotate the propeller forcefully—keep hands and body clear of the propeller arc.

Shop rags, safety wire ends, and tools must be accounted for and removed before closing any access panel. A foreign object left inside an aircraft is a Foreign Object Damage (FOD) hazard that can cause catastrophic failure.

Using the Discrepancy Log Correctly

Your discrepancy log is a legal document. Entries must be legible, dated, and signed. Do not erase—draw a single line through any error, initial it, and write the correct information. Each entry should stand alone: a reader unfamiliar with the aircraft must understand exactly what was found, where, how it was measured, and what the limit is. This practice directly mirrors the maintenance record entries you will make as a certificated A&P mechanic under 14 CFR Part 43.

Completing the Inspection

When your inspection sequence is complete, review the entire log before submitting. Confirm that every checklist item has a disposition—either within limits (record the value) or a discrepancy entry. Any safety-critical item found out of limits must be brought to the instructor's attention immediately and must not be closed out until proper corrective action is determined. Your thoroughness in this lab is a direct preview of your professional responsibility as an A&P mechanic.

Key terms9

Discrepancy LogA standardized written record of every maintenance finding, including the component, measured condition, applicable serviceable limit, and the FAA-approved reference used; it supports the maintenance decision-making process and becomes part of the aircraft records.
Serviceable LimitThe minimum or maximum value published in FAA-approved data (such as an AMM or overhaul manual) within which a component may remain in service without repair or replacement.
Differential Compression TestA powerplant inspection procedure that applies a regulated air pressure to a cylinder at top dead center on the compression stroke and measures the pressure drop across the piston, rings, and valves to assess cylinder health; results are compared to the engine manufacturer's minimum acceptable value.
Type Certificate Data Sheet (TCDS)An FAA-issued document that defines the approved configuration, limitations, and specifications for a certificated aircraft, engine, or propeller; it is primary FAA-approved data for maintenance decisions.
Lockout/Tagout (LOTO)A safety procedure that de-energizes electrical or mechanical systems and physically prevents re-energization during maintenance by applying a lock and identifying tag to the energy source.
Bore ScopeAn optical inspection tool inserted through a spark plug hole or access port to visually examine internal engine components—cylinder walls, piston crowns, and valves—without disassembly.
Insulation ResistanceA measurement, typically made with a multimeter or megohmmeter, that verifies the integrity of wire insulation by confirming that resistance between a conductor and ground or an adjacent conductor is above the minimum value specified in the wiring manual.
Foreign Object Damage (FOD)Damage caused to an aircraft or engine by a tool, rag, hardware, or any other object inadvertently left in or near the aircraft during maintenance; prevention requires strict tool accountability and area cleanup before closing any access.
ATA Chapter ReferenceA standardized numbering system used in aircraft maintenance manuals to organize maintenance tasks and components by system (e.g., Chapter 71 for powerplant, Chapter 27 for flight controls), enabling consistent cross-referencing across documentation.

Worked examples4

1. During a differential compression test on a four-cylinder engine, Cylinder 3 shows an input pressure of 80 psi and a differential (leakdown) pressure of 68 psi. The engine overhaul manual states the minimum acceptable differential compression is 60/80 psi (at least 60 psi retained out of 80 psi supplied). Is this cylinder within limits, and what do you record on the discrepancy log?
  1. Step 1 – Identify the test parameters: input pressure = 80 psi; pressure retained in cylinder = 68 psi.
  2. Step 2 – Compare to the published limit: the manual requires a minimum retained pressure of 60 psi when tested at 80 psi input.
  3. Step 3 – Evaluate: 68 psi retained ≥ 60 psi minimum required. The cylinder is within the serviceable limit.
  4. Step 4 – Record on the discrepancy log: 'Cylinder 3 differential compression: 68/80 psi. Engine overhaul manual minimum limit: 60/80 psi. Within limits. No discrepancy.' Include the manual name, revision, and section number.
Answer: Cylinder 3 is within limits (68 psi retained vs. 60 psi minimum). Record the actual value, the limit, the reference, and 'within limits'—no corrective action required.
2. Cylinder 2 on the same engine reads 52 psi retained out of 80 psi supplied, and audible air leakage is heard at the exhaust pipe. What is the finding, and what additional inspection step is required before you can complete the discrepancy log entry?
  1. Step 1 – Evaluate the reading: 52 psi retained is below the 60 psi minimum limit. This is an out-of-limits discrepancy.
  2. Step 2 – Identify the leak location: air heard at the exhaust pipe indicates a leaking exhaust valve.
  3. Step 3 – Perform a bore scope inspection through the spark plug hole with the cylinder at top dead center to visually confirm the condition of the exhaust valve seat and face.
  4. Step 4 – Record on the discrepancy log: 'Cylinder 2 differential compression: 52/80 psi. Engine overhaul manual minimum limit: 60/80 psi. OUT OF LIMITS. Air leakage audible at exhaust—suspected exhaust valve leak. Bore scope inspection performed: [describe findings]. Requires further maintenance action per overhaul manual.' Flag as a safety-critical discrepancy and notify instructor immediately.
Answer: Cylinder 2 is out of limits. The discrepancy log must record the measured value (52/80), the limit (60/80), the leak location (exhaust), bore scope findings, and the requirement for corrective action. Notify the instructor before proceeding.
3. You measure the right aileron down-travel with a protractor. Your reading is 14 degrees. The AMM states the serviceable range for right aileron down-travel is 15 degrees ± 2 degrees (13–17 degrees). Is this within limits?
  1. Step 1 – Identify the specified range: 15° ± 2° = 13° minimum to 17° maximum.
  2. Step 2 – Compare the measured value: 14° falls within the 13°–17° range.
  3. Step 3 – Conclusion: the measurement is within the serviceable limit.
  4. Step 4 – Record on the discrepancy log: 'Right aileron down-travel: measured 14°. AMM limit: 15° ± 2° (13°–17°). Within limits.' Include AMM section reference.
Answer: 14 degrees is within the 13–17 degree acceptable range. Record the measured value, the limit, the reference, and 'within limits.'
4. You measure the left aileron down-travel and obtain 11 degrees. The same AMM limit applies: 15° ± 2° (13–17 degrees). What is the finding, and what does a complete discrepancy log entry include?
  1. Step 1 – Identify the specified range: 13° minimum to 17° maximum.
  2. Step 2 – Compare: 11° is below the 13° minimum. This is out of limits.
  3. Step 3 – Record as a discrepancy: component (left aileron), measurement (11°), limit (15° ± 2°, minimum 13°), reference (AMM chapter and section), and disposition required (rigging adjustment per AMM procedure).
  4. Step 4 – Do not close the discrepancy until the appropriate corrective action is identified. Notify the instructor if flight controls are involved, as this is a safety-critical system.
Answer: 11 degrees is out of limits (below the 13° minimum). The discrepancy log entry must include the measured value, the published limit, the AMM reference, and the notation that corrective action is required. Flag as safety-critical.
In class: Conduct a systematic visual and operational inspection of airframe structural components, flight control rigging, and landing gear in accordance with the aircraft maintenance manual inspection checklist, recording actual measurements against published serviceable limits. · Perform engine and engine-mount inspection tasks including compression check, oil-system inspection, and ignition-system continuity check, documenting all findings with measured values and comparing to limits specified in the type certificate data sheet and engine overhaul manual. · Inspect avionics wiring, antenna installations, and instrument connections for security, chafing, and corrosion, using a calibrated multimeter to verify continuity and insulation resistance, and log all out-of-tolerance findings with wire identification and location.
Materials: Project aircraft or assembly; differential compression tester; calibrated torque wrenches (inch-pound and foot-pound ranges); multimeter (calibrated); bore scope; flashlight/inspection light; mechanic's mirror; aircraft maintenance manual; engine overhaul manual; type certificate data sheet; discrepancy log forms; safety wire; required PPE
Check: Instructor compares student's discrepancy log against a master list of seeded discrepancies; student must correctly identify 90% of seeded faults and provide an accurate measurement or observation for each; any safety-critical discrepancy missed requires immediate remediation and re-inspection before the project continues.

Practice check8

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

Aviation Maintenance Practices / Regulations
1. When entering a finding in a discrepancy log, which information is MOST important to include in addition to the component name and location?
Powerplant — Reciprocating Engines
2. A cylinder differential compression test is performed with 80 psi input. The retained pressure is 55 psi, and air is heard escaping through the carburetor air inlet. Which condition does this MOST likely indicate?
Powerplant — Reciprocating Engines
3. Before applying air pressure during a cylinder compression test, the piston must be positioned at:
Airframe — Electrical Systems
4. During an avionics wiring inspection, you find a wire bundle resting against a sharp metal bracket with visible wear to the outer insulation. The wiring beneath appears intact. What is the correct action?
Airframe — Flight Controls
5. Which document is the PRIMARY FAA-approved source for the maximum allowable control surface travel limits on a specific certificated aircraft?
Aviation Maintenance Practices / Safety
6. A student completes a multi-system inspection and submits a discrepancy log. The instructor's master list contains 20 seeded faults; the student correctly identified 17, missed 2 minor items, and missed 1 safety-critical cracked engine mount. What must happen before the project continues?
Aviation Maintenance Practices / Safety
7. Which lockout/tagout step verifies that a lockout has been successfully applied before beginning wiring work?
Regulations — 14 CFR / Aircraft Certification
8. The Type Certificate Data Sheet (TCDS) is BEST described as:
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