Spark Plug Removal, Inspection and Installation for the A&P Practical
Working with spark plugs on the Airframe and Powerplant (A&P) practical calls for careful removal, inspection, and installation. For the oral and practical (O&P) test, show the assigned procedure and explain the reason for each caution. Engine-specific steps, approved plug type, gap, rotation, torque, and anti-seize application are per the engine manufacturer’s instructions.
On this page
- What does the O&P practical evaluate?
- Start with the assigned data and a safe setup
- How do you make the task safe and preserve plug identity?
- How do you remove a plug without damaging it?
- What do you inspect before deciding to service or install it?
- How do you check spark plug gap?
- How do anti-seize, the gasket, and torque affect installation?
- How do you finish the installation?
What does the O&P practical evaluate?
The Federal Aviation Administration (FAA) Airman Certification Standards (ACS) list the hands-on skills below. A Designated Mechanic Examiner (DME) evaluates the assigned project against the performance standard in the downloaded test.
FAA Order 8900.1, Vol. 5, Ch. 5, Sec. 11, CHG 929, printed 16, PDF 16, 5-5-11-7C3)g)
Each practical project contains a skill element and two practical questions. You may use applicable reference material for both the skill and the questions.
FAA Order 8900.1, Vol. 5, Ch. 5, Sec. 11, CHG 929, printed 16, PDF 16, 5-5-11-7C3)c)
A project is pass/fail. Passing requires a successful skill demonstration on the first attempt and successful answers to both associated practical questions.
FAA Order 8900.1, Vol. 5, Ch. 5, Sec. 11, CHG 929, printed 16, PDF 16, 5-5-11-7C3)f)
The FAA Mechanic Test Generator (MTG) FAQ says projects are standalone. The two practical questions are asked at a safe and appropriate time during the project.
FAA Mechanic Test Generator FAQs, updated May 22, 2023, unnumbered page, PDF 4
The FAA sample test shows the project format: description, given equipment or information, performance standard, ACS code, references, and associated questions. It is marked for practice purposes only.
FAA sample oral and practical test, unnumbered page, PDF 6
Our study advice: use this guide to rehearse the sequence and explain your decisions. A published skill is a study target, not a promise that your downloaded test will assign this exact task.
| ACS skill | Exact published skill |
|---|---|
| AM.III.H.S3 | Remove, clean, and install spark plug. |
| AM.III.H.S11 | Inspect and check gap of spark plugs. |
| AM.III.H.S12 | Identify the correct spark plugs used for replacement installation. |
FAA-S-ACS-1, printed 52, PDF 57
Start with the assigned data and a safe setup
Use current maintenance and overhaul publications and procedures. The ACS safety appendix includes proper information and tools, equipment preparation, skill in handling tools, and required personal protective equipment (PPE), including safety glasses and hearing protection.
FAA-S-ACS-1, printed A-3, PDF 67
Disregard for safety will result in failure. If a project requires an action that would jeopardize safety, the evaluator will ask you to simulate that portion.
FAA-S-ACS-1, printed A-3, PDF 67
Our study advice: identify the applicable manufacturer’s instructions and any required approved data before starting. These handbook summaries do not replace the procedure for the assigned aircraft, engine, component, or equipment.
How do you make the task safe and preserve plug identity?
The handbook’s compression-test preparation directs the ignition switch to be OFF so there is no accidental firing before the accessible plugs are removed. The ACS also identifies working around an ungrounded magneto as an ignition-system risk.
FAA-H-8083-32B, Powerplant, Chapter 10, printed 10-39, PDF 39 · FAA-S-ACS-1, printed 52, PDF 57, AM.III.H.R3
The handbook’s ignition switch check shows why an ungrounded magneto is dangerous. If the engine does not cease firing with the switch in the off position, the magneto ground lead (P lead) is open and the trouble must be corrected: one or more magnetos are not being shut off even with the switch OFF. Turning the propeller of such an engine can result in personnel injury or death; the engine can start with personnel in the propeller arch. Our study advice: follow the assigned engine’s ignition and propeller precautions before handling the plugs or moving the propeller, and do not take an OFF switch position as proof that every magneto is grounded.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-31, PDF 31
Handle plugs individually. The handbook describes a drilled tray that prevents plugs from bumping together and helps identify each plug’s original location and proper rotation. A dropped spark plug should be discarded, because the shock of impact usually causes small, invisible insulator cracks.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-35, PDF 35
Our study advice: mark the tray by cylinder and plug position, then use the manufacturer’s applicable rotation instructions. Follow those instructions rather than a rotation pattern from memory.
How do you remove a plug without damaging it?
Disconnect the ignition harness lead before removing the plug. Pull the lead straight out in line with the plug barrel. A side load may damage the barrel insulator and ceramic lead terminal.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-35, PDF 35 · FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-36, PDF 36
Use the proper deep socket and keep it aligned with the plug while applying steady pressure. The handbook warns that a tilted socket damages the plug. Place removed plugs in the tray.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-36, PDF 36
What do you inspect before deciding to service or install it?
Start with a visual inspection. Check threads for damage, the lead shielding barrel for corrosion, nicks, and cracks, the firing-end insulator for cracks and chips, the electrodes for excessive wear, and the wrench hex for damage.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-36, PDF 36
If the plug passes visual inspection, the handbook describes degreasing, deposit removal, abrasive cleaning, and testing as a servicing sequence. Keep solvent out of the shielding barrel, never soak the plugs, and remove abrasive material with a thorough air blast after abrasive cleaning.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-36, PDF 36
Our study advice: use the servicing method specified for the assigned plug, with the required equipment and protection. The overview here is not authorization to use abrasive cleaning on every electrode design.
Check that a new or reconditioned plug is an approved type under the applicable manufacturer’s instructions. Inspect its threads, nose insulator, shielding barrel, and contact condition before installation.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-37, PDF 37 · FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-38, PDF 38
How do you check spark plug gap?
Use a round wire-thickness gauge for the massive-electrode gap described in the handbook. A flat gauge gives an incorrect clearance indication because those ground electrodes follow the shape of the round center electrode. Keep the wire gauge parallel to the center electrode’s centerline; tilting it gives an incorrect indication.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-38, PDF 38
Do not install a plug with a gap outside the specified clearance range. The actual gap setting and any adjustment method are per the engine manufacturer’s instructions and the applicable plug instructions; no universal gap value is supplied here.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-38, PDF 38
How do anti-seize, the gasket, and torque affect installation?
Keep graphite anti-seize off the ground electrode, center electrode, and plug nose. Graphite is an excellent electrical conductor and can cause permanent fouling; excessive thread lubricant reaching the electrodes causes shorting.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-35, PDF 35 · FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-38, PDF 38
The handbook gives two different placements for the compound: one passage says never to apply it to the first set of threads, and the installation steps say to coat the first two or three threads from the electrode end of the shell. Our study advice: use only the applicable manufacturer’s specified compound, quantity, and placement.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-35, PDF 35 · FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-38, PDF 38
The handbook calls for a new spark plug gasket. When a thermocouple gasket is used, do not add another gasket.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-38, PDF 38
Start the plug without a wrench and turn it by hand until it seats on the gasket. If high torque is needed during installation, the handbook identifies dirty or damaged threads as a cause. After finger seating, use a torque wrench to tighten to the specified torque.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-38, PDF 38
Excessive torque can distort the gasket and stretch the shell, leading to breakage on later removal or installation. Shell stretch opens the seal between shell and core insulator, causing loss of gas tightness or insulator damage.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-38, PDF 38
How do you finish the installation?
Inspect the lead terminal sleeve for damage before installation. Install the lead carefully in the shielding barrel and tighten the coupling elbow nut with the proper tool. After tightening, avoid checking tightness by twisting the elbow body.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-38, PDF 38 · FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-39, PDF 39
After all plugs are installed and torqued and the leads are correctly installed, the handbook calls for an engine start and a complete ignition-system operational check. Perform any engine operation under the applicable manufacturer’s procedure and safety precautions.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-39, PDF 39
Our rehearsal checklist: preserve plug identity, use the correct plug type, reject dropped plugs, protect the lead and insulators, verify the gap, keep anti-seize away from electrodes, hand-start the plug, apply the specified torque, and complete the required checks.
Frequently asked questions
Can I use a thread-cleaning tap on a Heli-Coil spark plug insert?
No. The handbook says never to clean Heli-Coil inserts with a cleaning tap because permanent insert damage results. If an insert is damaged, replace it under the applicable manufacturer’s instructions.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-37, PDF 37
Why does an enlarged spark plug gap matter?
As erosion enlarges the gap, the magneto must produce higher voltage. The handbook connects excessive gap with insulation breakdown, premature flashover, carbon tracking, misfiring, and hard starting.
FAA-H-8083-32B, Powerplant, Chapter 4, printed 4-35, PDF 35
Does an O&P spark plug project have the same scope as magneto timing?
No. The ACS lists separate skills for removing, cleaning, and installing a spark plug; checking its gap; and timing a magneto to the engine. Work to the assigned project’s scope and performance standard rather than adding another ignition task.
Rehearse the spoken answer with DMEReady
DMEReady is an AI voice examiner for the A&P oral. You answer out loud in your phone or computer browser, and it asks follow-up questions the way a DME would. You can rehearse an oral built from the ACS codes on your Airman Knowledge Test Report (AKTR). It rehearses the oral; it does not train hands-on practical skills. The first drill is free, with no sign-up. DMEReady is an AI examiner, not a human DME. It is independent and is not affiliated with or endorsed by the FAA. It does not predict or guarantee results.
Start your free drillFor examiner fees and planning, read the DME exam cost guide.
Oral coming up soon? Try the full thing free for 30 days
We are running a small pilot before launch. If your oral and practical is in the next few weeks, you get every section of the voice mock oral free for 30 days, no card. In return, tell us honestly what helped and what didn’t.
Start the free pilotLimited spots. The pilot closes on November 30.
Passed a written? Get your oral study plan by email
Paste the ACS codes on your Airman Knowledge Test Report (AKTR). We’ll email you a study plan now, then two short tasks built from your codes: one on day 3, one on day 7. That’s all.
Related guides
- Ignition and Starting Systems Oral Exam Questions and Answers
- Reciprocating Engine Oral Exam Questions and Answers
- Engine Inspection Oral Exam Questions and Answers
- Torque on the A&P Practical: Wrench Use, Extensions and Values
- Magneto Timing on the A&P Practical: Internal and External Timing
- A&P Practical Projects: What the DME Evaluates on the O&P
Sources
Primary sources checked October 20, 2026.
- FAA Order 8900.1, Vol. 5, Ch. 5, Sec. 11, CHG 929
- FAA Mechanic Test Generator FAQs, updated May 22, 2023
- FAA sample oral and practical test
- FAA-S-ACS-1
- FAA-H-8083-32B, Powerplant, Chapter 10
- FAA-H-8083-32B, Powerplant, Chapter 4
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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