Aircraft Logbook Abbreviations and Terms
This glossary explains abbreviations and terms that commonly appear in aircraft maintenance logbooks and records. Shops and owners use them inconsistently, so always read the full entry and any referenced work order before relying on an abbreviation. It is educational and is not a regulatory source. For requirements that apply to a particular aircraft, consult the current regulations, the manufacturer's data and a qualified maintenance professional.
For how these terms fit together in a real review, start with how to read aircraft maintenance logbooks.
Time and status terms
TT, TTAF and TTSN
Total time, total time airframe and total time since new. They usually refer to the airframe's accumulated flight time, but confirm which component an entry describes, because engines and propellers carry their own times.
TSN and SNEW
Time since new and since new. Always attach the figure to a specific component and serial number.
SMOH and TSMOH
Since major overhaul and time since major overhaul. These count time from a documented overhaul of an engine. Preserve the overhaul date and the shop paperwork behind it. A recent shop visit does not by itself mean an overhaul occurred.
STOH
Since top overhaul. It generally refers to time since cylinder (top-end) work, not an overhaul of the entire engine.
SPOH
Since propeller overhaul. The propeller has its own overhaul history, separate from the engine and airframe.
TBO
Time between overhaul, the interval a manufacturer recommends for an engine or component. For many operations under 14 CFR Part 91 it is a manufacturer recommendation rather than a regulatory limit, but applicability depends on the operation and any program the aircraft follows. Confirm it with the maintenance provider.
TSO
In logbooks this often means time since overhaul. Elsewhere, TSO stands for Technical Standard Order, an FAA minimum performance standard for specified articles. Context decides which meaning applies.
Tach time and Hobbs time
Two different instruments. Tach time is tied to engine speed, and Hobbs time generally runs while the aircraft is operating, so the readings are not interchangeable. If an instrument has been replaced, the old and new readings are separate counters. See oil-change intervals in aircraft records for how mixing clocks distorts an interval.
Life-limited part
A part with a mandatory replacement limit expressed in time, cycles or another measure. Its current status is a separate record question from whether an inspection was completed.
Inspections and maintenance
Annual inspection
An inspection required by 14 CFR 91.409(a) for most aircraft within the preceding 12 calendar months, performed by an appropriately certificated person. An annual entry documents a point-in-time inspection and does not answer every question about an aircraft's condition.
100-hour inspection
An inspection required by 14 CFR 91.409(b) for certain aircraft operated for hire or used for flight instruction for hire. Whether it applies depends on the operation.
A&P
An FAA-certificated mechanic holding airframe and powerplant ratings.
IA
Inspection Authorization, an additional authorization held by some A&P mechanics. It allows them to perform annual inspections and approve certain major repairs and alterations for return to service.
Return to service
The approval entry that records an aircraft or component as approved for return to service after maintenance or inspection. An inspection that lists discrepancies is not the same as an approval for return to service. See how to read aircraft maintenance logbooks.
Preventive maintenance
A defined category of simple maintenance listed in 14 CFR Part 43, Appendix A. Where owners are authorized to perform it, the recordkeeping requirements still apply.
Compression test
Usually a differential compression test that records how well each cylinder held pressure during a test. The numbers need engine identity, procedure and the mechanic's findings to mean anything. See understanding cylinder compression readings.
Hot section inspection (HSI)
A turbine-engine inspection of the hot-section components. It is a distinct event from an overhaul, and a record of one should not be described as the other.
Pre-buy inspection
An inspection a buyer arranges before purchase. The scope is agreed between the buyer and the shop, and the name alone does not establish what was included. See what to look for in aircraft logbooks before you buy.
Regulatory and approval documents
AD (Airworthiness Directive)
A legally enforceable FAA requirement addressing an unsafe condition in a product. Applicability depends on the exact model, serial number, installed components and modifications, and some ADs recur. A historical "complied with" entry is a starting point for review, not a current compliance determination.
SB, SI and service letter
Manufacturer service bulletins, service instructions and service letters communicate recommended or required actions. A service bulletin is not an AD, although an AD can make a bulletin's actions mandatory by reference.
STC (Supplemental Type Certificate)
An FAA approval of a major modification to an aircraft's type design. An STC alone does not show the modification was installed on a particular airplane. That requires the installation record.
Form 337
FAA Form 337, Major Repair and Alteration. It can document an alteration such as an equipment installation as well as a repair, so its presence does not by itself indicate an accident. See damage history in aircraft records.
Major repair and major alteration
Categories defined by FAA regulation (see 14 CFR Part 43, Appendix A). They are typically recorded on Form 337, although Part 43, Appendix B includes alternative recording provisions for certain repairs.
ICA (Instructions for Continued Airworthiness)
Manufacturer or approval-holder instructions for maintaining a product or modification after installation.
PMA part
A part produced under an FAA Parts Manufacturer Approval, typically by a manufacturer other than the original equipment manufacturer.
Entry shorthand
IAW
In accordance with. Follow it to the referenced document and revision.
C/W
Complied with. Identify the specific action and whether it recurs.
R&R
Removed and replaced, or removed and reinstalled. The surrounding sentence decides which.
Work order
A shop's record of tasks performed. A short logbook entry often points to a work order that holds the detail, so request it when an entry matters.
Aircraft-specific terms
CAPS
The Cirrus Airframe Parachute System. Its parachute, rocket and related components have their own maintenance events, so a single "CAPS service" entry does not establish the status of every component. See Cirrus SR22 maintenance records.
Weight and balance
The documented empty weight and center of gravity, updated when equipment changes. Check that the latest revision matches the current equipment list.
PlaneFacts reports support diligence. They do not establish current airworthiness or replace an aircraft inspection or a qualified maintenance review.