FAA Logbook Flight Time: Reconcile Hobbs, Tach and OUT/IN

Executive Summary

Logging flight time from a Hobbs meter, a tach meter, an OUT/IN pair or an onboard flight timer starts with one question: which interval did the device actually record? Under United States (FAA) rules, 14 CFR 1.1 defines "flight time" as pilot time that "commences when an aircraft moves under its own power for the purpose of flight" and "ends when the aircraft comes to rest after landing" ^[1]. The eCFR displayed that text as up to date as of 6 November 2026 ^[1]. 14 CFR 61.51 requires an entry of "Total flight time or lesson time" for each flight logged ^[2], but it does not say which instrument supplies the number.

The instruments disagree because they trigger on different events. In one documented Garmin GI 275 implementation, the HOBBS timer runs while an engine registers oil pressure above 5 PSI, while the TACH timer scales with RPM against an installer-determined cruise setting, and a separate flight timer runs while airborne ^[3]. Airline OUT and IN times are gate events: brake release after doors close, and brake set at arrival ^[4]. None of these is identical to the 1.1 interval, so a difference between them is expected, not a defect.

This report therefore supplies a worksheet, not a multiplier. In a synthetic ordinary flight, an engine-based meter ran 75 minutes, airborne time was 46 minutes, and independently documented own-power movement to final rest was 65 minutes. The three numbers describe three intervals. No percentage adjustment is applied, because published trade estimates of the Hobbs-to-tach gap differ and depend on the installation ^[5].

Ground interruptions need extra facts. FAA legal interpretations from 2004 and 2016 held that, in the fact patterns presented, flight time continued to accrue while the flightcrew was required to remain onboard ^[6]. Both arose outside the personal logbook, and neither lets a reader log every engine-on or pushback minute. Where the facts are missing (was movement under own power, was the crew required onboard, was the stop temporary or final), the correct worksheet state is "unresolved", with a question for the operator or the FAA, not an invented answer.

Finally, keep the original reading and add a reviewed value beside it. The worksheet below is a manual method that works beside any logbook, including the publisher's own invitation-only Pilot Logbook (disclosed here), which does not publicly document a Hobbs or tach reconciliation feature.

Introduction and Background

Pilots who combine airline, charter and earlier general-aviation records meet the same problem repeatedly. A roster shows scheduled times, an airline system reports OUT, OFF, ON and IN, an avionics display shows a flight timer, and a rental airplane carries a Hobbs meter and a tach meter. The durations rarely match. The question for a personal logbook is not which clock is best, but which source supports the duration being entered, and which discrepancy needs more facts before anything is entered.

This report is scoped to FAA jurisdiction, to professional aeroplane pilots and to pilots building FAA experience, and it treats the logbook as a personal record. It does not reassess pilot-in-command or second-in-command credit, which depends on other provisions of 14 CFR 61.51. It also excludes maintenance procedures and duty-limit or dispatch decisions.

Sources carry different weight, and this report labels them:

• Binding rules: the eCFR text of 14 CFR 1.1 and 14 CFR 61.51.
• Historical interpretations: FAA legal letters reading a rule on specific facts, which are not the rule.
• Vendor claims: documentation for one product or installation, attributed to the vendor.
• Trade-press statements: general descriptions, labelled as such.
• Recommended audit steps: practice offered here, not a requirement.

Existing coverage deserves acknowledgement. Pilot Institute's article on pilot logbook time, posted 27 December 2021 and updated 26 January 2022, already explains the 1.1 definition, the clocks and de-icing ^[7]. This report does not claim novelty in those basics. Its contribution is a source-to-duration worksheet that links each recorded interval to the rule, the equipment documentation and the open facts, and that keeps unresolved cases explicit.

Key Rules and Interpretations

The 14 CFR 1.1 definition of flight time

14 CFR 1.1 opens with "As used in this chapter, unless the context requires otherwise" ^[1], so its definitions apply across the FAA's regulations unless context says otherwise. The definition of flight time has two parts. For most aircraft, flight time is pilot time that begins when the aircraft moves under its own power for the purpose of flight and ends when it comes to rest after landing ^[1]. A second part covers gliders without self-launch capability and starts at tow.

Three features matter for a logbook. First, the start is a movement event, not an engine-start or door event. Second, the movement must be under the aircraft's own power and for the purpose of flight, so a tug-driven pushback is not by itself the start. The FAA's 2014 interpretation to Johnson (the "Johnson 2014" letter, distinct from the 2016 letter discussed below) makes the same distinction when it says the time counts "unless the aircraft is not moving under its own power" ^[8]. Third, the end is rest after landing, not wheels-on.

The same section defines a different interval for maintenance records. "Time in service" runs from the moment an aircraft leaves the surface until it touches it at the next point of landing ^[1]. That is an airborne interval, and it is not the flight-time interval. Treating the two as interchangeable is the root of many Hobbs and tach disputes.

14 CFR 61.51 as logbook context

14 CFR 61.51 is titled "Pilot logbooks". Paragraph (a) requires a person to "document and record the following time in a manner acceptable to the Administrator" ^[2]. Paragraph (b) requires "each person must enter the following information for each flight or lesson logged" ^[2], and one item is "Total flight time or lesson time." ^[2]. The eCFR showed 61.51 as up to date as of 5 November 2026 ^[2].

Two observations follow from the text reviewed for this report. The section names total flight time as an entry but does not define how the duration is measured, so the measurement comes from the 1.1 definition. And it contains no wording that mandates paper or electronic form, only "a manner acceptable to the Administrator". Separately, paragraph (i) obliges a person to present the logbook on reasonable request ^[2], which is the practical reason a reviewed value should be traceable to a source.

The FAA's 2004 Kania interpretation

The FAA's letter of 29 April 2004 to Randall Kania responded to a request about "the crediting of the flight time limitations" under Part 121 ^[6]. It is a duty-limit document and does not discuss logbook entries. The requester's position was that a return to the gate, with no takeoff or landing, produced no flight time for the original taxi out and taxi in.

The FAA did not agree that a temporary suspension of a flight always suspends the accrual of flight time ^[6]. The decisive fact in the gate-return discussion was onboard presence. Where the "carrier requires the pilot to remain on board the airplane" ^[6], the letter treats the gate-return as a delay that "does not interrupt the accrual of" flight time ^[6]. It relied on the FAA's earlier de-icing position, and it also addressed a replacement aircraft that completes the flight after a return.

Scope limits matter. The letter concerns Part 121 limitations and notes that accrued time must still be "credited toward the cumulative flight time limits" ^[6]. The letter is silent on a pilot who is not required to remain onboard. It should not be converted into a universal logging entitlement.

The FAA's 2016 Johnson interpretation

The letter of 5 August 2016 to the Air Line Pilots Association (the "Johnson 2016" letter, a different letter from the 2014 Johnson interpretation cited earlier) is titled "Re: Termination of flight time under 14 C.F.R." 1.1 ^[9]. It answers four scenarios:

• Scenario 1: a flight "diverts for weather into COS, fully intending to continue", parked remotely with no passengers deplaning ^[9].
• Scenario 2: the same, except that stairs are "brought to the aircraft at COS allowing some passengers but not the flightcrew to deplane." ^[9]
• Scenarios 3 and 4: after landing at the destination, the aircraft is held at a remote location because no gate is available, or stops after leaving the runway because of traffic congestion ^[9].

The FAA reads Kania as holding that once flight time begins, "it continues to accrue as long as the pilot is required to remain" onboard ^[9]. It ties that to the 1.1 words "comes to rest": "Thus, an aircraft does not come to rest after landing while the flightcrew is" required to remain ^[9]. The conclusion for the scenarios is that the aircraft "has not come to rest after landing and flight time would" continue ^[9].

The scope of the 2016 letter is limited: it interprets the 1.1 definition on stated facts and does not mention logbooks. If the crew is not required to remain onboard, or the facts differ, it does not decide the case. A contrast case comes from a 2013 Federal Register clarification: "An empty plane that is parked at a customs gate has come to a rest." ^[10] No FAA interpretation, rule or notice modifying the 2004 Kania letter or the 2014 and 2016 Johnson letters is cited here; that is an absence in the sources checked, not proof that none exists.

Other jurisdictions, for contrast only

The definitions differ by authority, and a logbook entry should follow the rule of the authority it is meant to satisfy. The European Union operator rule ORO.FTL.105 starts flight time when an aircraft is "first moving from its parking place for the purpose of taking off" (Source: www.easa.europa.eu) and ends it only when the aircraft is at rest "on the designated parking position and all engines or propellers are shut down" (Source: www.easa.europa.eu). Transport Canada's advisory circular calls the Canadian definition "consistent with the current Federal Aviation Administration" definition ^[11]. None of these replaces 14 CFR 1.1 for an FAA record.

What Each Recorded Source Actually Measures

The practical method is to name the event behind each number before comparing numbers. Table 1 below sets the common sources against the event they record, who or what creates the record, and what the source cannot establish by itself.

No single source is a stand-in for the 1.1 interval, so a discrepancy is read from each source's trigger, not from a conversion factor.

Roster and reported actual times

A roster is a plan. Reported actual times are different: the United States Bureau of Transportation Statistics (BTS) Technical Reporting Directive #40, effective 1 January 2026, defines gate departure as the moment the pilot "releases the aircraft parking brake after passengers have loaded and aircraft doors have been closed" ^[4]. If the brake was not set at boarding, it uses "the time that the passenger door was closed" ^[4]. Gate arrival is when "the pilot sets the aircraft parking brake after arriving at the airport gate" ^[4]. Systems that rely on a docking guidance system record gate departure "when the aircraft moves more than 1 meter" and subtract a fixed offset to get the "out" time ^[4].

Three facts follow:

• Reporting scope: these are reporting definitions for carriers, not pilot-logbook rules.
• Sensed or typed: the directive states that carriers use "automated and/or manual systems for collecting flight data" ^[4], so a reported OUT may be sensed or entered by hand.
• Last departure: when a flight returns before takeoff, the directive requires "the last gate departure time before wheels-off time" ^[4], so a reported OUT can be the last of several departures.

An FAA ASPM (Aviation System Performance Metrics) help page adds that "When OOOI times are not available, they are estimated." ^[13] A downstream OOOI figure may therefore be modeled and not observed.

The BTS glossary gives the arithmetic vocabulary: elapsed time is "from gate departure time to gate arrival time" ^[14], and in-flight time runs "from wheels-off at the origin airport to wheels-down at the destination airport" ^[14]. These are reporting intervals. The 1.1 interval does not map onto any one of them.

Onboard flight timers, Hobbs and tach

A Garmin GI 275 flight manual supplement (AFMS 190-02246-12, Rev. 11, printed page 58) is one documented equipment implementation. It states that the flight timer increments whenever the airborne state is true, and that the state is "triggered via a weight on wheels switch, GPS ground" speed, airspeed or engine RPM depending on the aircraft installation ^[3]. It states that the HOBBS timer runs while one engine registers more than 5 PSI of oil pressure ^[3], and that the TACH timer increments by engine RPM "compared to the cruise power setting for" the engine, a setting determined by the installer ^[3].

This is one product in one documented configuration. The Garmin source cited here is the AFMS; other revisions of Garmin documentation, including the GI 275 Pilot's Guide, and other installations may differ. A display label alone does not prove a trigger. The actual aircraft's approved manual or installer documentation is the evidence.

Independent descriptions show how much the meters vary. An engine-monitor maker describes a tach counter "activated whenever the EDM senses RPM", where "High RPM values cause Tach Time to count faster" ^[15] and Tach Time "will count slower than HOBBS Time" at low RPM ^[15]. Aircraft Owners and Pilots Association (AOPA) material says "Most are activated by a pressure switch connected to the oil system" ^[5], but a meter "can measure the time that the electrical system is on" ^[5], and some meters "can be activated by an airspeed switch" ^[5]. Because of that spread, "Hobbs" names a meter type, not a fixed interval.

Rental billing versus the personal record

The Hobbs-versus-tach question often begins with billing. AOPA reports that "Most flight schools use the Hobbs meter to bill aircraft rental fees" ^[5] and that "Flying clubs often bill their members by tach time" ^[16]. Billing basis is a commercial agreement. It determines what is charged, not what the 1.1 definition would call flight time, so a rental invoice is a source to record in the worksheet with its basis noted.

How electronic logbooks name these fields

Electronic logbooks offer several bases for a total. MyFlightbook documents "Block Out" as "when airplane started movement under its own power" ^[17] and "Block In" as "when airplane came to rest at the end of flight" ^[17]. Its author describes mobile settings that "tie the total time field to block, hobbs, engine, or flight times" ^[18]. ForeFlight's support article states that its Out time is filled from "The time of the first recorded data point, up to 30 minutes before liftoff." ^[19], and that In is set "Approximately 15 minutes after landing detection." ^[19], while its import template defines TimeOut as "Time the aircraft starts moving from the gate or ramp." ^[20]. LogTen documents "a few ways to calculate Total Time" (Source: intercom.help).

The same label (Out, In, Block) can be filled by pilot entry, by track-log inference or by import, and vendors define it differently. Table 3 in the next section sets these side by side with Pilot Logbook.

Implementation Considerations and Process Changes

The source-to-duration worksheet

The worksheet is a record, one row per source per flight, followed by a reviewed value. It is a manual method and works on paper, in a spreadsheet or in any electronic logbook. Table 2 lists the columns and fills one row from the hypothetical flight used in the Data Analysis section.

Table 2 puts the trigger column before the candidate-value column on purpose. A source whose trigger is unknown can still be recorded and calculated, but it cannot by itself support a candidate flight-time value. The "unresolved" state is a legitimate end state for a row. A row marked unresolved is better than a plausible number with no basis.

How to apply the columns, in order:

• Identify the jurisdiction and category. For an FAA record, the interval of interest is the 1.1 flight time. Block time, if used, is a separate column.
• Name the event. Scheduled, reported actual, pilot-observed, aircraft-timer or billing counter.
• Match to the definition. Does the source capture own-power movement start, and rest after landing?
• Compare intervals without a factor. Subtract only values from the same flight, and record the difference as a difference, not a rate.
• Classify any ground interruption using the checklist below, then decide the candidate value or mark the row unresolved.

A recommended audit step, not a requirement: when two sources disagree by more than the unit of precision, do not choose the larger one. Write the unresolved fact, and ask the party who owns that fact.

Ground interruptions: an evidence checklist

Gate returns, diversions and remote holds are where the 2004 and 2016 interpretations matter. The checklist below asks for facts. It does not decide legality or logging eligibility, and it does not extend those letters beyond their stated scope.

• Did movement for flight begin? Evidence: own-power movement time from a pilot note, operator record or movement log. A tug pushback is not by itself own-power movement.
• Was the movement cancelled before takeoff? The requester in Kania argued that no flight time accrued on a return to the gate with no takeoff. The FAA did not agree that a temporary suspension always suspends accrual, and the deciding fact was onboard presence.
• Was the crew required to remain onboard during the stop? Evidence: operator instruction, procedure or crew communication at the time. This is the factual premise in all four 2016 scenarios ^[9].
• Is the stop temporary or final rest? A source that cannot distinguish the two (an OUT/IN pair, a meter) cannot answer this alone. The 2013 clarification's empty aircraft at a customs gate is a contrast case ^[10].
• Was there a tow or other non-own-power movement? A 2014 FAA letter distinguishes post-flight taxi that "is not done for the purpose of flight" ^[21].
• Was a second aircraft used? Kania treats a replacement aircraft as a distinct situation, so record each aircraft's span separately.
• What does the source capture? Record whether the source has a continuous record of the stop, only its endpoints, or nothing.

If the answers are missing, the row is "unresolved: facts required". The appropriate authority for the question is the operator's flight-operations or training department for operator facts, and FAA Flight Standards or the Office of the Chief Counsel for interpretive questions. This report does not decide it.

Recording a reviewed correction

61.51 as codified in the text reviewed contains no correction procedure. A defensible practice, offered as a recommendation, has five parts:

• Keep the original. Retain the original reading or timestamp and its source, unaltered.
• Add a reviewed value. Enter it in a separate field or line, marked as reviewed, with the date.
• State the basis. Name the source and the definition used, for example "1.1 interval from operator movement record".
• State the open facts. If the review leaves an item unresolved, say so.
• Keep the invoice and the display reading. A rental invoice or a photo of a meter reading is evidence of that source only.

Software varies in how much of this it supports. LogTen documents that "You can also manually overwrite any time that is calculated automatically if needed." (Source: intercom.help), and also offers a setting that adjusts calculated totals "by Percent or Minutes" (Source: intercom.help). A global adjustment is a convenience, not a substitute for a per-flight basis, and should be recorded in the worksheet as a policy with its reason.

Inspecting how an export presents the reviewed value

Before relying on an electronic logbook, export or print one test flight with a deliberately different meter reading and reviewed value, then check which fields appear: the total, the OUT/IN pair, the meter readings, the reviewed flag, the note. ForeFlight's version 14 logbook guide, dated January 2022 (as of that date; later versions of the app may behave differently), states that "The Hobbs Start and End fields are manually" entered ^[22]. Rounding also changes outputs: ForeFlight's guide says decimal "times are rounded to the nearest tenth." ^[22], whereas MyFlightbook by default "rounds everything to a whole minute, adds those minutes, and then divides by 60" ^[23]. The same flights can therefore total differently across products, and a worksheet should state the rounding rule used.

Table 3 below compares how several electronic logbooks name and treat the fields relevant here, drawn from each vendor's own pages. It is not a ranking.

"Total" is configurable in several products, so which source feeds it is a setting the pilot must check and record. Vendor entries are the vendors' own statements and were not independently tested here. The Pilot Logbook row reflects the publisher's description of its own product.

Data Analysis and Evidence

A synthetic ordinary flight (Hypothetical Example)

The numbers below are stipulated for illustration. They are not measurements, and no real performance or error-rate benchmark is available for the gap between these sources. The example excludes pushback, extended relief crews and interrupted-flight issues, and it does not establish any pilot's role-based logging eligibility.

• An engine-based meter interval runs 09:55 to 11:10, which is 75 minutes.
• Independently documented own-power movement begins at 10:00.
• Airborne time runs 10:12 to 10:58, which is 46 minutes.
• Final rest occurs at 11:05.
• Movement to final rest, 10:00 to 11:05, is 65 minutes.

On these stipulated facts, the 1.1 interval is 65 minutes. The meter shows 10 minutes more, because it started 5 minutes before own-power movement and stopped 5 minutes after final rest. The airborne timer shows 19 minutes less, because the 46-minute airborne interval excludes 12 minutes of movement before takeoff and 7 minutes after landing. The values disagree because the intervals differ, not because any one is wrong. Treating wheels-off to wheels-on as all pilot time, or adding a flat percentage to a tach reading, would produce a number unrelated to the documented interval.

Converting for a decimal logbook is a presentation step. 65 minutes is 1.083 hours, which a tenth-of-an-hour logbook would show as 1.1. Pilot Institute's article states that "Incomplete flight hours are added as tenths of a whole hour." ^[7]. The rounding rule belongs in the worksheet because products differ, as noted above.

Why no fixed multiplier is used

Published estimates of the Hobbs-to-tach gap exist, but they differ and they are not specifications. AOPA's 2018 article says "Tach time typically is 10 percent to 20 percent lower than Hobbs time" ^[5], while an AOPA aircraft-leasing guide says "Tachometer time lags Hobbs time by approximately two tenths per hour" ^[28]. Pilot Institute's article states that "There can be up to a twenty percent difference in Hobbs time and Tach time" ^[7]. These are general statements by publishers, not measured results for any aircraft. The engine-monitor maker's description above shows why: tach time accumulates as a function of current RPM against a configured cruise value, so the gap changes with the RPM profile of the flight. An older AOPA article adds that a Hobbs on oil pressure counts "the same no matter how fast the engine is running" ^[29]. This report adopts none of the percentages, and the worksheet records the actual difference for the actual flight.

Case Studies and Real-World Examples

Ordinary flight, three clocks (Hypothetical Example)

A first officer reviews a general-aviation leg before an airline application. The rental invoice and meter give 75 minutes, the avionics timer 46 minutes, and the pilot's own note records own-power movement at 10:00 and final rest at 11:05. The candidate 1.1 value is 65 minutes, supported by the note. The meter and timer rows are kept as intervals that differ for stated reasons, and the Hobbs trigger is marked unresolved until the aircraft's equipment documentation is obtained. Nothing about role credit is decided.

Gate return with the crew aboard (Hypothetical Example)

A captain's operator record shows OUT at 15:05 and OFF at 15:18. The captain's own notes add that the aircraft first moved under its own power at 14:20 and returned to the gate at 14:41, with the crew onboard during the stop. The operator's reported OUT is the later one, consistent with the BTS reporting rule requiring "the last gate departure time before wheels-off time" ^[4], so the first departure does not appear in the reported pair at all. The checklist asks whether movement for flight began at 14:20, whether the crew was required onboard, and whether the stop was temporary. The 2004 Kania letter and the 2016 Johnson letter addressed fact patterns in which the crew was required to remain onboard, but they were written for Part 121 limitations and for the 1.1 definition respectively, not for this pilot's logbook. If the notes do not record that the crew was required to remain aboard, the row stays unresolved and the question goes to the operator and, if needed, FAA Flight Standards.

Implications and Future Directions

A logbook that stores only a total hides the choice of source, while one that stores source readings, the chosen value and the basis lets a later reviewer see the choice. As electronic logbooks add automation, the question shifts from arithmetic to provenance: where an Out time is inferred from track data, as in ForeFlight's description ^[19], the record should say so.

On the form of the record, the FAA's Advisory Circular 120-78B says electronic signature and recordkeeping use under Part 61 "does not require formal FAA approval, acceptance," or authorization ^[30]. The circular states that such documents "do not have the force and effect of law and are not meant to bind" the public ^[30], so it is guidance on electronic records, not a rule for individual pilots. 61.51 itself asks only for "a manner acceptable to the Administrator" ^[2]. No FAA statement was found that a specific logbook product is approved.

The eCFR text of 1.1 was current as of the retrieval date, and the interpretations discussed are historical. Readers who depend on a specific outcome should check the current text and ask the FAA or their operator, because a later interpretation could narrow or extend these letters.

For the publisher's own Pilot Logbook (disclosed; invitation-only), the fit is limited: it does not publicly claim to reconcile Hobbs and tach readings or adjudicate eligibility, so keep the worksheet beside it for flights where the sources disagree. Readers can request an invite.

Frequently Asked Questions (FAQs)

What is the difference between Hobbs time and tach time in a logbook?

They are two counters triggered by different conditions. In one documented configuration, Hobbs runs while oil pressure exceeds 5 PSI and tach scales with RPM against a cruise setting ^[3]. Neither is defined by 14 CFR 1.1, which defines flight time by movement and rest. Record both readings, then record the 1.1 interval separately.

Can I log Hobbs time as flight time?

Only if the Hobbs interval matches the 1.1 interval for that flight, and that depends on the meter's trigger: a meter can be wired to oil pressure, to the electrical system or to an airspeed switch ^[5]. The Hobbs value is a source in the worksheet, and the equipment documentation decides whether it can support a candidate value.

How do I log flight time under FAA rules?

Enter the total flight time among the 61.51(b) items ^[2], using the 1.1 definition of the interval. Role-based categories such as pilot-in-command time follow other paragraphs of 61.51 and are outside this report.

What does 14 CFR 61.51 require in logbook entries?

It requires documentation "in a manner acceptable to the Administrator", with entries per flight including total flight time, and it requires presenting the logbook on request ^[2]. It does not define how the duration is measured.

How do I calculate flight time from block time?

The reviewed text of 1.1 and 61.51 contains no definition of block time. The BTS gate times are event definitions: OUT is a brake release after doors close ^[4]. To go from block to the 1.1 interval, find the own-power movement start and the rest after landing, and compare them with OUT and IN. Do not assume the two are equal.

What are OUT, OFF, ON and IN times?

The FAA's ASPM help describes them as the actual movements "Gate Out, Wheels Off, Wheels On, and Gate In" ^[13]. Gate times bound block time; wheels times bound airborne time. BTS requires actual times in local time ^[4], so note the time zone.

Does Hobbs versus tach matter for rental billing?

It matters for the bill. AOPA reports that most flight schools bill on Hobbs and some clubs on tach ^[5]. That arrangement does not by itself determine the logbook entry.

What is the FAA definition of flight time for a pilot logbook?

The definition in 14 CFR 1.1 ^[1]. 61.51 uses the term "flight time" without redefining it.

Are electronic pilot logbooks acceptable to the FAA?

61.51 asks for "a manner acceptable to the Administrator". FAA Advisory Circular 120-78B, discussed under Implications below, describes no formal FAA approval for Part 61 electronic recordkeeping and is guidance, not a rule for individuals.

Conclusion

The question behind "how to log flight time, Hobbs versus tach" is which interval each device records. Under 14 CFR 1.1, flight time runs from own-power movement for flight to rest after landing. A Hobbs meter, a tach meter, an onboard flight timer and an OUT/IN pair each trigger on something else, and none is a general stand-in for that interval. In the synthetic example, 75, 46 and 65 minutes describe three intervals of one flight, and the difference is information, not error.

The practical method is short. Name the event behind each source, record its trigger from the aircraft's own documentation, compute differences without conversion factors, and classify ground interruptions with the facts the 2004 and 2016 interpretations turned on, without extending them. Keep the original reading, add a reviewed value with its basis, and mark what cannot be established as unresolved. These steps are recommended practice, and they do not replace an operator's procedures or an authority's decision.

The publisher's own product, Pilot Logbook (disclosed above), is one place to keep OUT and IN entries and a calculated block time, alongside the manual worksheet described here. It is invitation-only, so a reader interested in it can request an invite.