Cotter Pins and Safety Methods for the A&P Practical
The Airframe and Powerplant (A&P) oral and practical (O&P) test includes hands-on work. For cotter pin installation A&P work, prepare to identify the specified pin, torque and align the castellated nut correctly, and finish the pin without creating a sharp hazard. Other safety devices have their own applications; choosing a different device is not an automatic substitute for the specified one.
On this page
- What does the O&P practical evaluate?
- Which safety method belongs on this connection?
- How do I torque and align a castellated nut?
- How do I select and form the cotter pin?
- What should I check before calling the pin complete?
- How do snap rings differ from cotter pins?
- Which cotter-pin mistakes should I catch?
- How should I rehearse before test day?
What does the O&P practical evaluate?
The Federal Aviation Administration (FAA) Airman Certification Standards (ACS) identify the skills below. A Designated Mechanic Examiner (DME) evaluates the assigned project against its stated performance standard, including your selection of appropriate tools and data. Each project has a skill element and two practical questions. The project is pass/fail: the skill demonstration must succeed on the first attempt, and both practical questions must be answered successfully. These study topics do not promise a particular test assignment.
FAA Order 8900.1, Vol. 5, Ch. 5, Sec. 11, para. 5-5-11-7C3), p. 16
| ACS skill | Exact published skill |
|---|---|
| AM.I.E.S2 | Determine and properly torque aircraft hardware. |
| AM.I.E.S5 | Select and install aircraft bolts. |
These are the broader hardware-torque and bolt-installation skills related to cotter pin work. The ACS does not list a separate skill for installing cotter pins.
Follow the applicable manufacturer’s instructions and approved data for the assigned work. The ACS safety appendix calls for current maintenance publications, safe tool handling, equipment preparation, safety glasses, hearing protection, and any other required personal protective equipment (PPE). Disregard for safety will result in failure. If a project action would jeopardize safety, the evaluator will ask you to simulate that portion.
Use Advisory Circular (AC) 43.13-1B only within its applicability. The FAA status page describes its methods for inspection and repair of nonpressurized areas of civil aircraft only when no manufacturer repair or maintenance instructions exist; the data generally concerns minor repairs. For major repairs, the repairs identified in the AC may only be used as a basis for FAA approval. The repair data may also be used as approved data, with the AC chapter, page, and paragraph listed in block 8 of FAA Form 337, when the user has determined that the data is appropriate to the product being repaired, directly applicable to the repair, and not contrary to the manufacturer’s data.
FAA AC 43.13-1B Active status and applicability
Which safety method belongs on this connection?
Aircraft safetying methods include safety wire, cotter pins, lockwashers, snap rings, and special nuts. Select the method specified for the connection rather than treating the list as interchangeable choices. This guide concentrates on cotter pins and snap rings; use the safety wire practical guide for the wire-installation task.
FAA-H-8083-30B, General, p. 7-75
How do I torque and align a castellated nut?
Find the specified torque before installing the cotter pin. Start with the recommended minimum torque plus applicable friction drag, then align a nut slot with the bolt hole without exceeding the maximum torque plus drag. If alignment cannot be reached within that limit, change the washer or nut and try again as directed by AC 43.13-1B. Do not exceed the limit merely to reach the next slot.
How do I select and form the cotter pin?
The cotter pin diameter should be the largest size that will fit consistent with the diameter of the cotter pin hole and/or the slots in the nut. The pin should fit neatly with very little play. Cotter pins should not be reused on aircraft. Form the legs with a reasonable bend radius: a sharp angled bend invites breakage. The following outline describes the common over-bolt-and-nut arrangement, not every approved pin configuration.
- Insert a correctly sized new pin through the aligned hole and nut slot.
- Bend the prong over the bolt end so it seats firmly against the bolt shank and does not extend beyond the bolt diameter.
- Bend the other prong down so it lies firmly flat against the nut and does not contact the washer.
- Finish the ends so they do not create an injury hazard; AC 43.13-1B notes that the end can be rolled and tucked. Then inspect the seating and bends.
FAA-H-8083-30B, General, p. 7-80 · AC 43.13-1B, p. 7-26
What should I check before calling the pin complete?
Check the pin’s fit, the direction and length of the bent prongs, and the absence of sharp exposed ends. The prong bent over the bolt should bear firmly against the shank; the prong against the nut should not end on the washer. In the optional wrapped-prong method, the prongs should not project beyond the sides of the nut. Verify the finished arrangement against the applicable installation data rather than mixing details from different methods.
AC 43.13-1B, p. 7-26 · FAA-H-8083-30B, General, p. 7-80
How do snap rings differ from cotter pins?
A snap ring is a spring-metal retaining ring that seats in a groove. Use the pliers designed for its type. An external ring fits an outside groove; an internal ring fits an inside groove. The General handbook says external snap rings may be safety wired but internal snap rings are never safetied. That description does not authorize an extra safety method contrary to a component’s instructions. Snap rings may be reused only while their shape and spring action are retained.
FAA-H-8083-30B, General, p. 7-80
Which cotter-pin mistakes should I catch?
Catch an undersized or loose-fitting pin, a reused pin, a sharp bend, a prong that extends too far over the bolt, a leg resting on the washer, and an unfinished sharp end. Also check the preceding torque operation: a neatly bent pin does not make an overtorqued nut acceptable. Correct the connection using its applicable data before treating the safetying as complete.
FAA-H-8083-30B, General, p. 7-80 · AC 43.13-1B, p. 7-26 · AC 43.13-1B, p. 7-7
How should I rehearse before test day?
Our study suggestion: work through cotter pin installation with an instructor, name the applicable source before selecting tools or values, and inspect the finished work against that source. Keep a note of the step you need to repeat in supervised practice. Rehearse the explanation separately from the physical task.
Frequently asked questions
Will the DME hand me the exact tools and data during the O&P practical?
Not directly. The examiner should not hand the specific tools and data directly to the applicant. The examiner must ensure the needed tools, equipment, and materials can be found, then evaluate the applicant’s selection of the appropriate tools and data.
FAA Order 8900.1, Vol. 5, Ch. 5, Sec. 11, para. 5-5-11-7C3), p. 16
May a spring pin replace a cotter pin?
A spring pin should not be used as a substitute for a cotter pin. Use the retaining device specified for the installation rather than choosing one only because it fits the hole.
Which cotter pins are identified for nonmagnetic or corrosion-resistant applications?
AN381 or MS24665 cotter pins are identified for locations where nonmagnetic material or corrosion resistance is desired. Select the specified material and part for the actual application.
Which direction should a clevis pin head normally face?
A clevis pin is normally installed with its head up or forward. That orientation helps prevent the pin from falling out if the cotter pin fails or works out; it is not a universal head-direction rule for every type of aircraft pin.
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Related guides
- Safety Wire Practical Test: Double-Twist and Turnbuckles
- Aircraft Hardware and Materials Oral Exam Questions and Answers
- A&P General Oral Questions: The Complete Breakdown
Sources
FAA sources checked October 19, 2026.
- FAA-S-ACS-1
- FAA AC 43.13-1B Active status and applicability
- FAA Order 8900.1, Volume 5, Chapter 5, Section 11, Administer an Oral and a Practical Test: Mechanic Applicant Under Part 65 Subpart D (CHG 929, 9/17/2024), para. 5-5-11-7C3)
- FAA-H-8083-30B, General
- AC 43.13-1B with Change 1, editorial update
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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