ATA Chapters Explained: Which Tasks Are B1, B2, or Both

One of the most common questions from engineers building or reviewing their logbook is simple to ask and surprisingly hard to answer cleanly: is this ATA chapter mine to sign as B1, B2, or does it depend? This guide gives you a practical working reference — and explains why a handful of chapters will never fit neatly into either box.

The honest starting point: there's no single official EASA table

Worth saying clearly, before the table below: EASA Part-66 does not publish one binding ATA-chapter-to-category list. The B1/B2 split is defined by the nature of the system — mechanical, structural and powerplant work under B1; avionics, electrical and electronic systems under B2 — not by a fixed chapter number. The actual legal authority for who signs what, on a specific aircraft type, at a specific organisation, is your company's Maintenance Organisation Exposition (MOE) and the type's maintenance programme.

What follows is the practical classification used across most training syllabi and company procedures — genuinely useful as a working reference, but not a substitute for your organisation's own task allocation rules.

Typically B1 (mechanical) chapters

| ATA | Chapter | |---|---| | 05 | Time Limits / Maintenance Checks | | 07 | Lifting and Shoring | | 08 | Leveling and Weighing | | 09 | Towing and Taxiing | | 12 | Servicing | | 20 | Standard Practices — Airframe | | 25 | Equipment / Furnishings | | 28 | Fuel | | 29 | Hydraulic Power | | 32 | Landing Gear | | 35 | Oxygen | | 36 | Pneumatic | | 51–57 | Structures | | 61 | Propellers | | 71–80 | Powerplant (mechanical) |

Typically B2 (avionics) chapters

| ATA | Chapter | |---|---| | 22 | Auto Flight | | 23 | Communications | | 24 | Electrical Power | | 31 | Indicating / Recording Systems | | 34 | Navigation | | 39 | Electrical / Electronic Panels | | 42 | Integrated Modular Avionics | | 45 | Central Maintenance System | | 46 | Information Systems |

The chapters that are genuinely mixed

This is the part most reference lists skip, and it's where logbook entries most often get mis-tagged:

| ATA | Chapter | Why it splits | |---|---|---| | 21 | Air Conditioning | Mechanical ducting, valves and packs = B1. Electronic controllers and sensors = B2. | | 27 | Flight Controls | Mechanical linkages, cables, actuators = B1. Fly-by-wire computers and sensors (increasingly common on modern types) = B2. | | 30 | Ice and Rain Protection | Pneumatic/mechanical anti-ice = B1. Electric heating elements and their controllers = B2. | | 33 | Lights | Fixtures and wiring installation can be B1; the electrical/electronic control systems are B2. | | 44 | Cabin Systems | Physical installation = B1. IFE and cabin electronics = B2. | | 73 | Engine Fuel and Control | Mechanical fuel system = B1. FADEC/EEC (the engine's electronic control unit) is squarely B2 territory on modern engines. | | 77 | Engine Indicating | Sensor installation is often B1; the signal processing and indicating system is B2. |

On these chapters, the honest answer to "is this task B1 or B2" is: it depends on which part of the system the specific task touches, not the chapter number alone. A task replacing a mechanical actuator on ATA 27 is B1. A task troubleshooting the flight control computer on the same ATA chapter is B2. Same chapter, different privilege — and this is exactly the scenario dual-licence engineers run into most often.

Why this matters for your logbook, not just your exam

Getting this classification right matters for two practical reasons:

Recency accuracy. If a mixed-chapter task is logged under the wrong category, it either inflates a recency count that shouldn't be credited, or — more commonly — fails to credit a category that should have counted. Over a 24-month rolling window, a handful of misclassified entries on chapters like 21, 27 or 73 can be the difference between showing current and showing lapsed at the exact moment it matters.

Audit defensibility. A quality department or authority reviewing your logbook will look at whether the licence category on each entry matches the actual privilege exercised. "I always tag ATA 73 as B1" doesn't hold up if the specific task was FADEC troubleshooting — that's B2 work, full stop, regardless of which chapter it lives under.

A practical rule of thumb

When a chapter is mixed, ask what the task actually touched:

Physical, mechanical, structural work (removing, installing, rigging, servicing a mechanical component) → B1
Electrical, electronic, software-level diagnosis or component work (troubleshooting a computer, testing a sensor circuit, working with wiring/avionics boxes) → B2
Both, genuinely (e.g. removed a mechanical actuator and diagnosed the associated electronic controller in the same task) → log it as dual-category, provided your certification reflects work under both privileges

Tracking mixed-chapter tasks without second-guessing yourself

This is exactly why a logbook needs a licence category field independent of the ATA chapter, not tied to it — the chapter tells you what system, the category tells you which privilege you exercised, and on chapters like 21, 27, 30 and 73 those two things don't always point the same way. AirMXTrack logs both fields on every entry, so a mixed-chapter task can be tagged accurately — including as dual-category when genuinely earned — without the ATA chapter forcing an assumption that doesn't match what you actually did.

Track ATA chapters and licence categories correctly, automatically → airmxtrack.com

AirMXTrack is a digital maintenance logbook built by a Licensed Aircraft Engineer, for Licensed Aircraft Engineers. Free to start, no credit card required.

Note: the classifications above reflect common industry practice and are provided as a practical reference only. Always follow your organisation's Maintenance Organisation Exposition (MOE) and the specific aircraft type's maintenance programme for authoritative task allocation.