FAA Mechanic Airman Certification Standards (ACS) Explained

The FAA Aviation Mechanic Airman Certification Standards (ACS), document FAA-S-ACS-1, is the authoritative blueprint for what an A&P mechanic must know and be able to do to earn a certificate. Every question on the General, Airframe, and Powerplant knowledge tests maps to an ACS code, and every task on the oral and practical exam traces back to an ACS skill element. Understanding the ACS structure helps you study smarter, interpret your test results, and prepare for the DME's oral questions.

Written by the AMTprep editorial team · Published · Last reviewed

Written against the FAA primary sources cited at the foot of this page.

What the ACS Is and Why It Replaced the PTS

Before 2023, FAA mechanic exams were guided by the Practical Test Standards (PTS). The ACS replaces the PTS with a more structured, task-based framework that explicitly links each knowledge area to the test questions that assess it. Where the PTS listed tasks, the ACS maps each task to specific knowledge codes (which drive the written test) and skill elements (which drive the O&P). This unified document eliminates the disconnect between the written test and the practical exam — both now trace back to the same standard.

The Three ACS Sections: General, Airframe, and Powerplant

The Mechanic ACS is divided into three sections corresponding to the three FAA knowledge tests and the two mechanic ratings. The General section covers subjects common to both ratings: regulations (14 CFR Parts 43, 65, 91), ground operations, weight and balance, fluid lines, NDT (nondestructive testing), mathematics, physics, and electrical fundamentals. The Airframe section covers aircraft structures (sheet metal, composites, wood/fabric), systems (hydraulics, pneumatics, fuel, ice protection), and instruments/communication/navigation. The Powerplant section covers reciprocating and turbine engines, engine instruments, propellers, and fuel and ignition systems.

ACS Code Format: How to Read AM.I.A.K1

Each item in the ACS has a unique code in the format AM.<Section>.<Area>.<Subject/Code>. For example, 'AM.I.A.K1' breaks down as: AM = Aviation Mechanic; I = General section (Roman numeral); A = Subject Area A within that section; K1 = Knowledge item 1. Knowledge items (K codes) appear on the written tests. Skill items (S codes) are assessed during the O&P. When you fail a written test, your Airman Knowledge Test Report (AKTR) lists the ACS codes of the questions you missed, so you can target those exact areas in your review. AMTprep tags every practice question to its ACS code so you can drill precisely where you need it.

How the ACS Drives the Written Tests

The FAA question bank for the three knowledge tests is built from the ACS knowledge codes. Each question is tagged to one or more ACS codes, and the tests are drawn from this pool. The General test has 60 questions, the Airframe test 100 questions, and the Powerplant test 100 questions. A score of 70% or higher is required to pass each test. The ACS lists the reference materials (AMT handbooks, FAA regulations, manufacturer's manuals) that are the authoritative source for each knowledge item — these are the same materials you should use when studying rationales for practice questions.

How the ACS Drives the Oral and Practical Exam

During the O&P exam with a DME, the examiner selects tasks from the ACS skill elements relevant to the rating(s) you are seeking. Each skill element specifies what you must demonstrate and the acceptable performance standard. The DME is required to evaluate you against the ACS — not against their personal preferences. If you are tested on a task, the ACS is your authoritative guide for what 'passing' looks like. Reviewing the skill elements before your O&P helps you anticipate exactly what the DME will ask you to do or explain.

Finding and Using the ACS in Your Study Plan

The Mechanic ACS is a free public-domain document available from the FAA website. Download FAA-S-ACS-1 and use it as your study guide framework: map every topic you study to its ACS code, and cross-reference the listed reference materials. When using AMTprep, the ACS code on each practice question tells you which section, area, and knowledge item you are being tested on. After any practice session or written test, use your weak ACS codes to guide your review — this is the most efficient way to close knowledge gaps before the exam.

Knowledge, Risk Management, and Skill Codes

Every element in the ACS carries a letter that tells you how it will be examined, and the three letters correspond to three different kinds of preparation.

K is Knowledge. These are the facts, relationships and procedures you are expected to know, and they are what the written test samples. A knowledge element is examinable on the multiple-choice test and again verbally at the oral.

R is Risk Management. These elements describe the hazards associated with a task and the ability to recognise and mitigate them — the consequences of an incorrect torque, of returning an aircraft to service with an unresolved discrepancy, of working outside the approved data. Risk elements are rarely tested well by multiple choice, so they surface mainly in the oral, where an examiner asks what could go wrong and what you would do about it.

S is Skill. These are the things you must be able to do with your hands and with the publications: perform an inspection, make a repair, locate the applicable data, complete a maintenance record entry. Skill elements are the practical portion of the exam.

The practical consequence is that a candidate who prepares only for K elements is prepared for one third of the standard. The knowledge test is the part of certification that a question bank alone can carry you through, and it is also the smallest part of what the ACS actually asks of you.

Turning an ACS Code Into a Study Session

A code on a page is not a study plan. The sequence that works is the same for every code.

Start by resolving the code to its subject area. AM.II.F.K3 is an element; AM.II.F is the area, Hydraulic and Pneumatic Systems. The area is the right unit because that is how the source material is organised and how questions are written.

Next, find the handbook section. Each area maps to specific chapters of FAA-H-8083-30B, -31B or -32B. Read the chapter before working a single question. Candidates who invert this order end up recognising answers without understanding systems, which passes a multiple-choice test at the margins and fails an oral immediately.

Then drill the area specifically, not the whole bank, and track the score for that area on its own. You want your practice number denominated in the same units as your test report, so that closing a gap is something you can observe rather than assume. Above 85 percent is where an area stops being a liability.

Finally, close the loop verbally. Say out loud what the system does, how it fails, and what you would inspect. If you cannot narrate it without the multiple-choice options in front of you, the knowledge is recognition-level and the oral will find that out.

What Changed When the ACS Replaced the PTS

The Practical Test Standards described what an examiner should test at the oral and practical. It did not connect to the written test at all, which meant the knowledge test and the practical exam were two separate documents that happened to cover overlapping material.

The ACS merged them. One document now defines the knowledge, risk management and skill elements for each subject area, and both the written test and the oral and practical are built from it. That single change produces the feature candidates care about most: your Airman Knowledge Test Report can list codes from the same standard the examiner is working from, so a missed question on the written test becomes a specific, named item on the oral.

This is why the fail report matters so much more under the ACS than it did under the PTS. It is no longer just a score breakdown; it is a list the examiner is directed to work through with you. A candidate with eight codes on their report is walking into an oral whose opening agenda has been published in advance and, quite often, not read.

The second change is subtler. By making risk management an explicit element type, the ACS put judgement on the examinable record rather than leaving it to examiner discretion. Expect to be asked not only how a system works but what happens if you get it wrong.

The Forty Subject Areas at a Glance

Across the three sections the ACS defines forty subject areas, and knowing how they are distributed tells you a good deal about how to plan study time.

Section I, General, has twelve areas and is examined on the 60-question General test: electricity and electronics, aircraft drawings, weight and balance, fluid lines and fittings, materials and hardware and processes, ground operations and servicing, cleaning and corrosion control, mathematics, regulations and records and publications, physics for aviation, inspection concepts and techniques, and human factors.

Section II, Airframe, has fifteen areas across 100 questions — the widest spread on any of the tests, running from metallic and non-metallic structures through flight controls, landing gear, hydraulics and pneumatics, environmental, instruments, communications, fuel, electrical, ice and rain, fire protection, rotorcraft and water and waste, plus airframe inspection.

Section III, Powerplant, has thirteen areas across 100 questions, anchored on reciprocating and turbine engines with the fuel, ignition, lubrication, electrical, instrument, fire protection, induction, air, exhaust and propeller systems around them, plus engine inspection.

The uneven arithmetic is the useful part. Twelve areas across 60 questions gives General a higher question density per area than Airframe's fifteen across 100, and Powerplant concentrates a large share of its questions in two of its thirteen headings. Study time allocated evenly across headings is study time allocated wrongly.

Frequently asked questions

Is the ACS the same as a study guide?
No. The ACS is a standard that defines what is tested and to what level, not a textbook. Think of it as the table of contents for your studies. You still need the AMT Handbooks and the FAA regulations as the actual content — the ACS tells you which parts of those references will be assessed.
What does the AKTR show me after a failed written test?
The Airman Knowledge Test Report (AKTR) lists the ACS codes of each question you answered incorrectly. Use these codes to look up the corresponding ACS knowledge items and the reference materials cited in the ACS — then study those specific sections and retake the test after 30 days.
Do I need to memorize the ACS codes themselves?
No. You do not need to recite ACS codes from memory during the exam. The codes are organizational identifiers used for study tracking and test reporting. What matters is understanding the subject matter each code represents.
Where can I download the Mechanic ACS?
The current Mechanic ACS (FAA-S-ACS-1) is available free on the FAA website at the URL in the primary sources section below. It is a public-domain document you are free to download, print, and share.
Where do I download the Mechanic ACS?
From faa.gov, in the airman testing and Airman Certification Standards section. It is a free PDF, it is the actual document your examiner works from, and it is worth having open while you study rather than relying on any summary of it. Check the revision date when you download it — the ACS is revised periodically, and preparing against a superseded edition is a real risk.
Do I need to memorise the ACS codes themselves?
No. Nobody is going to ask you to recite a code. What you need is the ability to go the other way: to take a code off your test report and turn it into the right chapter of the right handbook and the right set of practice questions. The codes are an index, and an index is useful for lookup rather than for memorisation.

ACS subject areas covered here

These are the FAA Mechanic ACS areas this guide maps to. Each page breaks the area down and carries free practice questions with worked rationales.

Primary sources

Related guides

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