The Commercial Pilot Airplane Knowledge Test (CAX) is the FAA written exam you must pass before sitting for the commercial pilot practical test. It's a 100-question, multiple-choice exam with a 3-hour time limit and a 70% passing score. This page walks you through exactly what's tested, how to prepare efficiently, and the regulatory requirements you'll be expected to know cold.
Quick facts about the CAX
- Number of questions: 100
- Time allowed: 3 hours
- Passing score: 70%
- Question format: Multiple choice, 3 answer choices
- Test fee: ~$175 at PSI testing centers (varies)
- Validity: Score is valid for 24 calendar months (you must take the practical within that window)
- Authorization required: Endorsement from an authorized instructor or completion of an FAA-approved home-study course
Eligibility to take the commercial written test
Before you can sit for the CAX, you need to meet the prerequisites in FAR 61.123. You must:
- Be at least 18 years old
- Be able to read, speak, write, and understand English
- Hold at least a private pilot certificate (or meet equivalent requirements)
- Have received and logged ground training, or completed a home-study course covering the aeronautical knowledge areas in FAR 61.125
- Receive an endorsement from an authorized instructor certifying you're prepared
Note that you do not need to have completed your commercial flight training hours under FAR 61.129 before taking the written. Most students take the CAX earlier in their training so the score doesn't expire mid-checkride prep.
What's on the commercial pilot written test
The FAA's Commercial Pilot Airman Certification Standards (ACS) drives the test content. Questions are pulled from the ACS knowledge codes across these subject areas:
Aeronautical knowledge areas (per FAR 61.125)
- Federal Aviation Regulations — Parts 61, 91, and applicable NTSB 830 reporting
- Accident reporting under NTSB Part 830
- Basic aerodynamics and the principles of flight applicable to commercial operations
- Meteorology — recognition of critical weather situations, windshear, frontal systems
- Safe and efficient operation of aircraft including high-performance and complex airplane considerations
- Weight and balance computations
- Performance charts — takeoff, landing, climb, cruise
- Significance and effects of exceeding operating limitations
- Use of aeronautical charts and a magnetic compass for pilotage and dead reckoning
- Use of air navigation facilities
- Aeronautical decision making (ADM) and judgment
- Principles and functions of aircraft systems
- Maneuvers, procedures, and emergency operations appropriate to the aircraft
- Night and high-altitude operations
- National Airspace System procedures for commercial operations
- Procedures for flight and ground training for lighter-than-air ratings (if applicable)
Subject area weighting (approximate)
| Subject area | Approx. % of test |
|---|---|
| Regulations (Parts 61, 91, NTSB 830) | 15–20% |
| Aerodynamics & performance | 15–20% |
| Weather & weather services | 10–15% |
| Weight & balance, performance charts | 10–15% |
| Aircraft systems (incl. high-altitude, complex) | 10% |
| Navigation & charts | 10% |
| ADM, human factors, physiology | 5–10% |
| Airspace & airport operations | 5–10% |
Weights shift slightly with each FAA test bank update — but if you can defend yourself in every row above, you'll clear 70% comfortably.
Hardest topics on the CAX (and where students lose points)
After watching thousands of students prep, the recurring problem areas are:
- Weight and balance shift problems — moving cargo, adding/removing passengers, computing new CG
- Performance chart interpolation — pressure altitude, density altitude, headwind components
- High-altitude physiology — hypoxia types, time of useful consciousness, supplemental oxygen rules under FAR 91.211
- Commercial-specific regs — the carry-over from private to commercial under Part 91 vs. when Part 119/135 starts to apply
- Holding pattern entries and timing (less weighted but easy to miss)
- Loss of control / stability and control questions
Commercial vs. private written test: what's actually different
| Private (PAR) | Commercial (CAX) | |
|---|---|---|
| Questions | 60 | 100 |
| Time limit | 2 hr 30 min | 3 hours |
| Passing score | 70% | 70% |
| Aerodynamics depth | Introductory | Deeper — stability, load factor, V-speeds for performance |
| Performance charts | Basic | Multi-step interpolation |
| Systems | Basic | High-performance, complex, retractable, constant-speed prop, turbocharging |
| Regs focus | Part 61/91 fundamentals | Commercial privileges/limitations, holding out, common carriage |
The CAX is not the IRA (instrument written) — but if you took the IRA recently, the weather and chart questions will feel familiar.
A realistic 4–6 week study plan
Week 1 — Regulations & ADM
- Read Part 61 Subpart F (Commercial Pilots) end to end
- FAR 61.123 eligibility, FAR 61.129 experience requirements
- Commercial privileges and limitations under FAR 61.133
- NTSB 830 reportable events
Week 2 — Aerodynamics & performance
- Stability, load factor, maneuvering speed, V-speeds
- High-performance and complex airplane systems (constant-speed prop, retractable gear, turbocharging)
- Work 20+ performance chart problems by hand
Week 3 — Weight & balance + weather
- All four weight-shift formulas until they're automatic
- METAR/TAF/PIREP/AIRMET/SIGMET decoding
- Frontal weather, thunderstorms, icing, windshear
Week 4 — Navigation, airspace, systems review
- Sectional and IFR low-altitude chart symbology
- Airspace dimensions and entry requirements
- High-altitude operations and oxygen rules (FAR 91.211)
Week 5 — Full-length practice tests
- Three to five full 100-question simulated exams under timed conditions
- Review every missed question and tag the ACS code
Week 6 — Targeted weakness drills + endorsement
- Drill only the ACS codes you missed
- Get your CFI endorsement
- Schedule the test
Where to take the test
The CAX is administered at PSI Services testing centers (the FAA's current contractor). You'll need:
- FTN (FAA Tracking Number) from IACRA
- Government-issued photo ID
- Instructor endorsement or home-study course completion certificate
- Test fee (~$175, subject to change)
The test is computer-based. You'll get a printed Airman Knowledge Test Report (AKTR) at the end with your score and the ACS codes for every question you missed — bring that AKTR to your checkride; the DPE will quiz you on each missed code.
How GroundScholar helps with this
GroundScholar runs a CAX prep mode that pulls from the current FAA test bank structure, tags every question to its ACS code, and adapts difficulty as you go. Miss a weight-and-balance shift problem and you'll see three more variants until you stop missing them — that's the adaptive drilling, not just a static question bank.
More importantly, every regulation answer is verified against the live CFR, so you're not memorizing a 2019-vintage explanation that's been amended twice. When you're ready, the mock checkride simulates a DPE walking through your missed-code AKTR — the same conversation you'll have at your real oral.
Ready to pass the CAX on the first attempt?
Don't show up at PSI hoping the curve is on your side. Drill the ACS codes, work the performance charts by hand, and walk in knowing exactly what you'll see.