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LEARN: AIRCRAFT LOGBOOKS

Part 1 of the Radar logbook series

How aircraft logbooks work.

Every jet has a second identity: its paperwork. Why records exist, the four logbooks, what one entry must say, the time numbers and inspections, on the real records of Challenger 350 N395PD. Then the same lesson written out below, with a glossary.

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Its paperwork

Sound on for the soundtrack; captions are on by default. Keys: Space plays and pauses, arrows skip 5 seconds, 0 to 7 jump to a chapter. Download the MP4.

THE SHORT VERSION

Twelve terms, one jet.

Each with its real example from N395PD’s records.

AWAirworthy
The aircraft conforms to its type design and is in condition for safe operation. It may fly only while both are true.
On N395PDAirworthiness date 23 Aug 2015
LogLogbook
The bound or digital record of every inspection, repair, alteration and part change for one unit: the airframe, an engine, a propeller or an APU.
On N395PDFour books: airframe, two engines, APU
EntryLogbook entry
The written record of one job. 14 CFR 43.9 sets what it must say; 43.11 adds more for inspections.
On N395PDEngine L, fuel filter, 12 Jun 2026
RTSReturn to service
The signed approval that lets the aircraft or unit fly again after the work in that entry.
On N395PDSigned by an A&P mechanic, certificate number on the entry
TTTotal time
Total time in service of the airframe, in hours. 91.417 requires it for the airframe, each engine and each propeller.
On N395PD3,434.1 hrs on 12 Jun 2026
TSNTime since new
Hours on a unit or part since it was built. Life limits and overhaul intervals are often counted from here.
On N395PDEngine P136235: 3,434.1 hrs
TSOTime since overhaul
Hours since a unit or part was last overhauled. It restarts at zero at each overhaul, while its time since new keeps counting.
On N395PDAn overhauled LPT stub shaft arrived with 4,648.98 hrs since new
CSNCycles since new
For engines, cycles counted under the maker’s definition, roughly one per flight. Many life-limited parts are counted in cycles, not hours.
On N395PDEngine P136235: 2,398 cycles
LDGLandings
The airframe’s own count of flights. Landing gear and some structure have limits in landings.
On N395PD2,386 landings on 12 Jun 2026
ANNAnnual inspection
A full inspection every 12 calendar months, the default for most small aircraft. A 100-hour inspection is added when the aircraft is flown for hire.
On N395PDNot used on this jet: it follows an inspection program
PROGInspection program
A schedule of inspection tasks due by hours, cycles and calendar time, often the manufacturer’s. Required for turbojet and other larger aircraft.
On N395PD12 and 24 month, 600 hour tasks, 15 Jul 2026
ADAirworthiness Directive
An FAA rule under 14 CFR Part 39 that fixes an unsafe condition. Mandatory. The records show each AD’s status and method of compliance.
On N395PDAD 74-08-09 R3 (k)

THE FOUR BOOKS

Each book keeps its own clock.

N395PD’s logbooks and their times on 23 Jan 2023, from the aircraft’s component times report. A jet has no propeller logs; turboprops and piston aircraft keep one per propeller.

Airframe logChallenger 350 · S/N 20577

2,061.3 hrs1,678 landings

Engine log, No. 1AS907-2-1A · S/N P136235

2,061.3 hrs since new1,689 cycles

Engine log, No. 2AS907-2-1A · S/N P136234

2,061.3 hrs since new1,689 cycles

APU logGTCP36-150(BD) · S/N P-662

2,173.75 hrsits own clock

Propeller logOne per propeller

Not on a jetturboprops and pistons

Airframe, engine and APU times of Challenger 350 S/N 20577 on 23 Jan 2023. Engines and APUs can move between aircraft; their logbooks move with them.

WHY RECORDS EXIST

An aircraft may fly only while it is airworthy. The records prove it.

Airworthy has a two part meaning in FAA rules: the aircraft conforms to its type design, and it is in condition for safe operation. Both depend on what has been done to it over its life, and the logbooks are where that is written down.

The owner or operator is responsible for keeping them. 14 CFR 91.417 lists what must be kept and for how long:

Records of maintenance, alterations and required inspections: a description of the work, the date, and the signature and certificate number of the person who approved the return to service. Kept until the work is repeated or superseded, or for one year.
Total time in service of the airframe, each engine, each propeller and each rotor.
Current status of life-limited parts, and time since last overhaul of items that must be overhauled on a schedule.
Current inspection status, and the status of every applicable AD with its method of compliance and, if it recurs, when it is next due.
A copy of the Form 337 for each major alteration.
The totals and status records stay with the aircraft and transfer to the next owner when it is sold (91.417(b)(2) and 91.419).

THE FOUR BOOKS

One logbook for each major unit.

An aircraft’s records are split by unit. The airframe log covers the structure, systems and avionics, plus inspections and ADs on the airframe. Each engine has its own log, each propeller has its own log, and an auxiliary power unit (APU) usually has one too.

N395PD is a Challenger 350, serial 20577. It has an airframe log, two engine logs (Honeywell AS907-2-1A, serials P136235 and P136234) and an APU log (GTCP36-150(BD), serial P-662). Jets have no propellers, so no propeller logs.

Engines, propellers and APUs come off for overhaul, get swapped and get sold. Their logbooks move with them. An engine installed on a different aircraft brings its own hours, cycles, inspections and ADs, so its book has to stay complete on its own. The airframe log records the removal and the installation; the engine log carries the engine’s history.

ONE ENTRY

What a logbook entry must say.

The film shows a real entry from N395PD’s left engine log, dated 12 Jun 2026: the No. 1 engine fuel filter and its O-rings were replaced per the Bombardier maintenance manual, then ops and leak checked. Under 14 CFR 43.9 a maintenance entry holds:

A description of the work, or a reference to data acceptable to the FAA. Here: the task and BD-100 AMM 73-10-05.
The date the work was completed: 12 Jun 2026.
The name of the person who did the work, if different from the person approving it.
If the work is approved for return to service: the signature, certificate number and kind of certificate of the person approving it. Here an A&P mechanic signed (the name and number are redacted on this page).
Shops also record the times: aircraft 3,434.1 hours and 2,386 landings, engine 3,434.1 hours and 2,398 cycles. An inspection entry must include the total time in service (43.11).

THE TIME NUMBERS

Every entry carries the clocks forward.

Each logbook keeps a running count. The airframe counts total time and landings. Each engine counts its time since new and its cycles. An APU counts its own hours. Parts that are overhauled on a schedule also count time since overhaul, which restarts at zero at each overhaul.

These counts are how anything with a limit is tracked: inspections due every so many hours, parts retired after so many cycles, overhauls at a set interval. They should only go up from one entry to the next. A count that goes backward, or a gap between entries, is a question for whoever is reading the records.

N395PD’s clocks, entry by entry. Engine figures are engine 1, S/N P136235.
DateSourceTT (hrs)LandingsEngine TSN (hrs)Engine cycles
23 Jan 2023Component times report2,061.31,6782,061.31,689
7 Dec 2023Flight log 0012,169.11,7772,169.11,789
28 May 2025Flight log 412,363.11,8882,363.11,900
12 Jun 2026Engine L entry3,434.12,3863,434.12,398

INSPECTIONS

On a schedule, then signed off.

Most small aircraft get an annual inspection every 12 calendar months under 14 CFR 91.409(a). If the aircraft carries people for hire or is used for flight instruction for hire, it also needs a 100-hour inspection (91.409(b)).

Large airplanes, turbojet multiengine airplanes, turboprop multiengine airplanes and turbine helicopters follow an inspection program instead (91.409(e)). The owner picks one of the programs in 91.409(f): a continuous airworthiness program, an approved aircraft inspection program, the manufacturer’s current recommended program, or one the FAA approves.

N395PD follows the manufacturer’s program. Its tasks come due by hours, cycles and months. On 15 Jul 2026, at 3,446.5 hours and 2,393 landings, the 12 and 24 month tasks, the 600 hour tasks and the APU 800 and 2,400 hour tasks were signed off, with a statement that the aircraft was inspected under the manufacturer’s recommended program per 91.409(f)(3), found airworthy and approved for return to service.

Annual and 100-hourInspection program
WhoMost small aircraft under Part 91Large airplanes, turbojet and turboprop multiengine airplanes, turbine helicopters
WhenEvery 12 calendar months; plus every 100 hours if flown for hireTask by task, due by hours, cycles or months
Rule14 CFR 91.409(a) and (b)14 CFR 91.409(e) and (f)
On N395PDNot usedManufacturer’s program: 12 and 24 month, 600 hour, APU 800 and 2,400 hour tasks signed off 15 Jul 2026

ADS, SBS AND TAGS

The paper behind the entries.

Entries also record Airworthiness Directives (FAA rules, mandatory), service bulletins (the maker’s notices) and the FAA Form 8130-3 release tags that come with parts. On N395PD: AD 74-08-09 R3 (k), Honeywell SB AS907-72-9094, and an 8130-3 for carbon seal S/N 26-169020-00568.

Part 2ADs, SBs and 8130s, on one real jobWatch the film →

THE LIFE STORY

Years of entries become one story.

Every date and number below is from the aircraft’s own records. Hours are airframe total time. Buyers, pre-buy inspectors and lenders read this story to decide what the aircraft is worth and whether it is what the seller says.

  1. ·Airworthiness date
  2. 2,061.3 hrsTimes report: 1,678 landings
  3. 2,169.1 hrsFlight log 001, as N575MW
  4. 2,363.1 hrsGround spoiler fault: thrust quadrant replaced
  5. 3,015.4 hrs600 hour package, AD 74-08-09 R3
  6. ·Entries now read N395PD
  7. 3,434.1 hrsNo. 1 engine fuel filter
  8. 3,446.5 hrsEngine shop visit, SB AS907-72-9094
  9. 3,446.5 hrs12 and 24 month inspections
Part 3How logbooks are judgedWatch the film →

ABOUT THIS EXAMPLE

Every value in the film and on this page comes from the records of one airframe, Challenger 350 serial 20577, registered N395PD (its entries read N575MW until April 2026): the component times report of 23 Jan 2023, airframe flight logs of 7 December 2023 and 28 May 2025, the left engine log entry of 12 Jun 2026, the 600 hour package of 10 February 2026, work order 39023 of 14 July 2026 and the inspection package of 15 Jul 2026. Shop and operator names, people’s names, signatures and certificate numbers are redacted. In the film, the engine log entry and the flight log are the real scans; the inspection sign-off is redrawn from the real entry; the books, cards and charts are drawn from the real values; the photographs of the hangar, engine and paperwork are illustrations, not this aircraft.

THE SERIES

Part 1: How aircraft logbooks work (this page)

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