Direct Answer — CVR & FDR Records Under Part 135
Under 14 CFR §135.151, a multiengine, turbine-powered airplane or rotorcraft with a passenger seating configuration of six or more requiring two pilots — or 20 or more seats — must carry an approved cockpit voice recorder, and §135.151(e) lets an erasure-equipped recorder erase audio recorded more than 15 minutes (paragraph (a) aircraft) or 30 minutes (paragraph (b) aircraft) earlier, while aircraft manufactured on or after April 7, 2010 must meet the TSO-tiered standard in §135.151(g) — at least the last 2 hours (TSO-C123a), rising to the last 25 hours (TSO-C123c) as it phases in. Under 14 CFR §135.152, the applicable aircraft must carry an approved flight data recorder, keep the recorded data until the aircraft has operated at least 25 hours (10 hours for a rotorcraft) per §135.152(d), and — critically for the records side — retain the most recent instrument calibration and the recorder correlation under §135.152(f). After a reportable event, both rules require preserving the recorded information for at least 60 days. The recorders themselves are hardware; what an inspector audits is the correlation, calibration, and preservation paperwork.
The recorder is hardware — the compliance lives in the documentation
A working CVR and FDR are necessary but not sufficient. The records angle of §135.152 is paragraph (f): the certificate holder must retain the most recent instrument calibration and the recorder correlation. That documentation — not the box in the avionics bay — is what an inspector asks to see, and what is missing when an operator gets a finding.
The Cockpit Voice Recorder — §135.151 Applicability and Retention
Section 135.151 is heavily amended, so the safest way to read it is in layers: who needs a CVR, how long it must retain audio, and what happens to that audio after an event. The applicability is keyed to turbine, multiengine aircraft above a seating/crew threshold — not to every charter aircraft.
14 CFR §135.151 requires an approved cockpit voice recorder on:
- Paragraph (a): a multiengine, turbine-powered airplane or rotorcraft with a passenger seating configuration of six or more and for which two pilots are required
- Paragraph (b): a multiengine, turbine-powered airplane or rotorcraft with a passenger seating configuration of 20 or more seats
The recorder must be operated continuously across the flight, and §135.151(e) governs erasure: an approved recorder with an erasure feature may erase information recorded in accordance with paragraph (a) and recorded more than 15 minutes earlier, or recorded in accordance with paragraph (b) and recorded more than 30 minutes earlier. That sets the legacy retention floor — the last 15 or 30 minutes of cockpit audio must always survive.
For aircraft manufactured on or after April 7, 2010, §135.151(g) raises the bar to a TSO-tiered standard — a recorder meeting TSO-C123a retains at least the last 2 hours, while the newer TSO-C123c requires the last 25 hours as it phases in (confirm which tier applies to your aircraft) — with §135.151(f) addressing the upgrade obligations for aircraft manufactured before that date. Section 135.151(h) addresses recording of datalink communications messages where the aircraft is required to carry both a CVR and an FDR.
Retention window ≠ records-retention schedule
The 15-minute, 30-minute, 2-hour, and 25-hour figures describe how much audio the recorder hardware must hold — a continuous-recording-duration spec. They are not how long you keep a piece of paper in a file. The records you keep are the installation and functional-check entries, the recorder correlation, and the post-event preservation evidence. Do not confuse the recorder's audio window with your document retention obligations — see the aviation records retention schedule for the paperwork side.
The CVR sits inside the broader required-equipment and records framework. For how these recorder records fit alongside the rest of an operator's obligations, see what records a Part 135 operator must keep, and for the maintenance-entry standard every recorder sign-off has to satisfy, see the §43.9 maintenance record entry requirements.
The Flight Data Recorder — §135.152 Applicability, Parameters, and Data Retention
Section 135.152 is one of the most amended sections in Part 135, with applicability and parameter requirements layered by seating configuration, aircraft type, and a series of manufacture and registration dates. Rather than recite every date, the durable points for the records-keeper are: which aircraft are covered, how long the data must be kept, and what documentation the certificate holder retains.
14 CFR §135.152 requires an approved flight data recorder on the multiengine, turbine-powered airplanes and rotorcraft it describes — generally tied to passenger-seating thresholds (such as the 10-or-more and 20-or-more seat bands) and to whether the aircraft was brought onto the U.S. register, or manufactured, after the applicable dates in the section. The number and type of parameters the FDR must record scale with the aircraft category and certification date, with the digital-parameter lists set out in the section and its referenced appendices.
On data retention, §135.152(d) requires the certificate holder to keep the recorded flight data until the aircraft has been operated for at least 25 hours (for the airplanes covered) or, for a rotorcraft, at least 10 hours — though a sufficient amount may be erased for testing the recorder, and no record need be kept more than 60 days. This is the trailing-window logic: the FDR overwrites continuously, but a minimum block of recent operating hours must always be preserved on the medium.
On recordkeeping, §135.152(f) requires that the most recent instrument calibration — including the recording medium from which that calibration is derived — and the recorder correlation be retained by the certificate holder. That documentation is the heart of the FDR records angle.
CVR vs FDR — Two Recorders, Two Records Profiles
| Attribute | CVR (§135.151) | FDR (§135.152) |
|---|---|---|
| What it records | Cockpit audio / crew communications | Flight parameters (attitude, speed, altitude, etc.) |
| Retention window | 15/30 min legacy; 2 hr → 25 hr TSO-tiered (built on/after Apr 7, 2010) | Until ≥ 25 hrs operated (10 hrs rotorcraft); ≤ 60 days |
| Key records obligation | Installation + functional-check entries; post-event preservation | Most recent calibration + recorder correlation retained |
| Post-event preservation | At least 60 days (§135.151(c)) | At least 60 days (§135.152(e)) |
| Part 91 analog | §91.609 CVR (15-min erasure) | §91.609 FDR |
Because the FDR is maintained under the operator's continuous-airworthiness arrangements, these records connect directly to the maintenance program. See Part 135 maintenance recordkeeping and CAMP requirements and Part 135 contract maintenance records for how a recorder correlation performed by an outside shop has to be captured and retained.
Related Aviation Compliance Guides
The Correlation, the Calibration, and the "Annual Readout" Question
This is the part operators most often get wrong, so it is worth slowing down. There is a widespread belief that §135.152 itself mandates a once-a-year FDR readout. The records-grounded version is more careful — and getting it right keeps you from either over-claiming a rule that does not exist or under-keeping documentation the rule does require.
- Retain the most recent instrument calibration, including the recording medium it is derived from — §135.152(f).
- Retain the recorder correlation — the documented verification that recorded parameters match the aircraft's instruments and configuration.
- Keep the recorded data on its trailing-hours window (25 hrs / 10 hrs rotorcraft; ≤ 60 days) — §135.152(d).
- Preserve data at least 60 days after a reportable event — §135.152(e).
Section 135.152 does not contain a numbered subsection setting a flat "one readout per year" calendar. A recurring FDR readout-and-correlation check — frequently described as annual — is driven by:
- The aircraft's airworthiness standards and the manufacturer's instructions for continued airworthiness.
- The operator's maintenance program and operations specifications.
- FAA guidance and advisory material on FDR continued serviceability.
Confirm the interval that actually applies to your aircraft with your maintenance program and FSDO — then keep the resulting readout/correlation documentation.
Why the distinction matters for an audit
If you cite a §135.152 "annual readout" subsection that does not exist, an inspector who knows the section will lose confidence in the rest of your program. If instead you say "§135.152(f) requires us to retain the current calibration and correlation, and our maintenance program schedules the readout/correlation at this interval" — and you can produce both — you have framed it the way the rule and the program actually work. Precision about what is in the CFR versus what is in your program is itself an audit signal.
The recorder correlation is conceptually similar to other recurring airworthiness verifications an operator has to keep current and provable — compare it to the cadence discipline in the §91.411 / §91.413 altimeter and transponder test records and airworthiness directive compliance records, both of which fail in the same way recorder paperwork fails: the work is done, but the document proving it is missing or stale.
Record Discipline — What an Inspector Actually Looks For
Recorder compliance is only as good as the records that prove it. Here is what a complete, audit-ready recorder record set looks like for a Part 135 operator — and the specific ways these records fail.
Complete Record Set
- CVR and FDR installation maintenance entries (make/model, TSO basis where applicable)
- The FDR recorder correlation documentation required by §135.152(f)
- The most recent instrument calibration, including the recording medium it derives from
- Any periodic recorder readout / functional-check records your maintenance program calls for, with dates
- Evidence of which CVR retention tier applies (legacy 15/30-min vs the TSO-tiered 2-hour/25-hour requirement for aircraft built on/after Apr 7, 2010)
- Post-event preservation records demonstrating §135.151(c) and §135.152(e) were followed when applicable
How These Records Fail
- No retained recorder correlation on file — the single most common §135.152(f) finding
- A stale instrument calibration with no current readout to anchor it
- Citing a non-existent §135.152 "annual readout" subsection instead of the program-driven interval
- Confusing the CVR audio retention window with a paper-records retention schedule
- Assuming the recorder is installed and working but having no maintenance entry that proves it
- After a reportable event, leaving data in the aircraft to be overwritten instead of preserving it
FileFlo as the Recorder-Records Proof Layer
FileFlo is a compliance document intelligence platform — a read-only proof layer that sits alongside your maintenance-tracking stack and completes it. It does not operate, read out, or maintain a CVR or FDR, perform correlations or calibrations, or run a maintenance-tracking, dispatch, or flight-operations system. What it does is make the records that prove recorder compliance instantly producible.
- Classifies uploaded recorder documents against their governing rule — installation entries, FDR recorder correlation and instrument calibration (§135.152(f)), and CVR functional-check records
- Tracks the next-due date your maintenance program assigns to the FDR readout/correlation and surfaces expiration alerts at 90/60/30 days
- Indexes the post-event preservation evidence so the §135.151(c) / §135.152(e) 60-day obligation is provable after an occurrence
- Flags a missing or stale recorder correlation or calibration before a surveillance inspector finds it
- Generates an inspector-format records binder on demand, organized by aircraft and requirement
FileFlo classifies 600+ compliance document types and manages records across Part 91, Part 135, and Part 145 operators in a single platform. Pricing: Starter $89/mo, Professional $299/mo. 5-day free trial, no credit card required. FileFlo keeps the documents that prove compliance audit-ready — it does not provide or run a safety management system (SMS), dispatch system, or flight operations system.
Part 135 vs Part 91 — Same Recorders, Different Accountability
The recorder hardware and the post-event preservation logic are very similar across the operating rules. What changes is who carries the obligation and how it is documented. Section 91.609 is the Part 91 counterpart: it requires an approved FDR and CVR on the applicable U.S. civil registered multiengine, turbine-powered aircraft, permits erasing CVR information recorded more than 15 minutes earlier under §91.609(f), and requires preserving recorded information at least 60 days after a reportable event under §91.609(g).
Who is responsible
Owner/operator
Carries the §91.609 recorder obligations directly. Most exposed to a missing correlation or a forgotten post-event preservation step with no program backstop.
Who is responsible
DOM via maintenance program / OpSpecs
The CVR and FDR fold into the §135.152(f) retention duty, the maintenance program, and the manuals. A Principal Maintenance Inspector reviews the correlation and calibration paperwork.
Who is responsible
Operator + maintenance org
Multiengine turbine aircraft above the seating thresholds are where recorders attach. The readout/correlation interval and documentation are managed through the maintenance program.
These recorder records sit alongside the other recurring obligations a Part 135 fleet must keep continuously provable. See how to prepare for a Part 135 FAA surveillance audit for how inspectors examine these records, the Part 91 §409 annual inspection requirements for another recurring interval cross-checked against the logbooks, and the FAA Part 135 SMS 2027 deadline for the broader records-readiness wave coming to charter operators.
Frequently Asked Questions
Which Part 135 aircraft must have a cockpit voice recorder under 14 CFR §135.151?
Per 14 CFR §135.151(a), no person may operate a multiengine, turbine-powered airplane or rotorcraft having a passenger seating configuration of six or more and for which two pilots are required by type certification or operating rule unless it is equipped with an approved cockpit voice recorder. Section 135.151(b) extends the requirement to a multiengine, turbine-powered airplane or rotorcraft having a passenger seating configuration of 20 or more seats. So the CVR trigger is fundamentally about a turbine, multiengine aircraft plus a seating/crew threshold — a single-pilot, piston, or small-cabin charter aircraft is generally outside §135.151. Verify your specific aircraft against the full text and your operations specifications, because the seating-configuration and two-pilot determinations drive the answer.
How long does a Part 135 CVR have to retain — what is the 15-minute, 30-minute, and 2-hour rule?
It depends on which paragraph the aircraft falls under and when it was manufactured. Under §135.151(e), an approved recorder with an erasure feature may erase information that was recorded in accordance with paragraph (a) and recorded more than 15 minutes earlier, or recorded in accordance with paragraph (b) and recorded more than 30 minutes earlier. That is the legacy floor: the last 15 or 30 minutes of cockpit audio must survive. For aircraft manufactured on or after April 7, 2010, §135.151(g) sets a TSO-tiered standard: a recorder meeting the older TSO (TSO-C123a) retains at least the last 2 hours of recorded information, while the newer TSO (TSO-C123c) requires retaining the last 25 hours as it phases in — confirm which tier and TSO apply to your specific aircraft. So a newer turbine aircraft keeps at least two hours, and up to the last 25 hours on the newer standard, while an older one operating under the legacy provision keeps a minimum 15 or 30 minutes. The retention window is a hardware/recording-duration requirement, not a records-filing retention schedule.
What does §135.152 require a flight data recorder to keep, and for how long?
Section 135.152 sets out which multiengine, turbine-powered airplanes and rotorcraft must carry an approved flight data recorder and which flight parameters it must record, keyed to seating configuration, aircraft type, and manufacture/registration dates. On retention, §135.152(d) requires that the certificate holder keep the recorded data until the aircraft has been operated for at least 25 hours (for the airplanes covered) or, for a rotorcraft, until it has been operated for at least 10 hours — although a sufficient amount may be erased for testing, and no record need be kept more than 60 days. In other words the FDR continuously overwrites, but a minimum trailing block of operating hours must always be preserved. After a reportable accident or incident, the rule requires the recorded data to be kept for at least 60 days, or longer if requested.
Is there an annual FDR readout or correlation check required by 14 CFR §135.152?
This is a common point of confusion, so be precise. Section 135.152 itself does not contain a numbered subsection mandating a once-a-year FDR readout. What §135.152(f) does require is that the certificate holder retain the most recent instrument calibration — including the recording medium from which that calibration is derived — and the recorder correlation. The correlation is the documented verification that the parameters the recorder captures actually match the aircraft's instruments and configuration. A recurring readout-and-correlation check on a defined interval (often described as annual) is driven by the aircraft's airworthiness standards and continuing-airworthiness program and by the operator's maintenance program and operations specifications, not by a flat 14 CFR §135.152 calendar interval. Confirm the actual interval that applies to your aircraft with your maintenance program and FSDO; what §135.152 unambiguously requires is that you retain the current calibration and correlation documentation.
What recorder records does an FAA inspector actually expect to see at a Part 135 operator?
An inspector reviewing recorder compliance typically wants to see, for each affected aircraft: the maintenance record entries showing the CVR and FDR are installed and operational; the documentation of the FDR recorder correlation and the most recent instrument calibration that §135.152(f) requires the certificate holder to retain; any periodic recorder readout or functional-check documentation called for by the aircraft's maintenance program; and evidence that, after any reportable event, the recorded information was preserved per §135.151(c) and §135.152(e). They are checking that the recorders are airworthy, that the correlation/calibration paperwork exists and is current, and that the operator knows how to preserve the data when an event occurs. Missing correlation or calibration documentation is treated the same as not having done it.
What must happen to the recorded information after an accident or incident?
Under §135.151(c), in the event of an accident or occurrence that requires immediate notification to the National Transportation Safety Board and that results in termination of the flight, the operator must keep the recorded cockpit-voice information for at least 60 days or, if requested by the Administrator or the Board, for a longer period — and the information may be used only as the rule permits. Section 135.152(e) imposes the parallel obligation for flight data recorder data after a reportable event: preserve it for at least 60 days, or longer on request. Operationally, that means the moment a reportable event occurs the recorders should be secured and the data pulled and preserved, not left in the aircraft to be overwritten. The Part 91 analog in §91.609(g) uses the same 60-day floor.
How do Part 91 recorder rules in §91.609 compare to the Part 135 rules?
Section 91.609 is the general-operating-rules counterpart. It requires an approved flight data recorder on U.S. civil registered multiengine, turbine-powered airplanes and rotorcraft with the applicable seating configuration and manufacture date, and an approved cockpit voice recorder where the aircraft has six or more passenger seats and two pilots are required. The CVR erasure provision in §91.609(f) permits erasing information recorded more than 15 minutes earlier, and §91.609(g) requires keeping recorded information for at least 60 days after a reportable event. The recorder hardware and preservation logic are very similar across Part 91 and Part 135; what differs is the operator accountability layer — a Part 135 certificate holder owns these obligations through its maintenance program, operations specifications, and manuals, whereas a Part 91 operator carries them directly.
Does FileFlo run, read, or maintain the cockpit voice recorder or flight data recorder?
No. FileFlo is a compliance document intelligence platform — a read-only proof layer. It does not operate, read out, download, or maintain a CVR or FDR, perform recorder correlations or calibrations, or run a maintenance-tracking, dispatch, or flight-operations system. What FileFlo does is classify and index the recorder records — the correlation and calibration documentation §135.152(f) requires you to retain, the installation and functional-check maintenance entries, and the post-event preservation records — then track the next-due dates your maintenance program assigns and surface expiration alerts so a stale correlation or calibration never surprises you in a surveillance audit. The recorder work itself is performed by your maintenance organization and an appropriately rated repair station.
Never let a recorder correlation or calibration go stale on you
FileFlo classifies your CVR and FDR records, indexes the §135.152(f) correlation and calibration documentation, tracks the readout/correlation next-due date your maintenance program assigns, preserves the post-event evidence, and generates a complete inspector-format records binder on demand. Starter plan $89/mo. Professional $299/mo. 5-day free trial — no credit card required.
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Written by Chad Griffith, Founder & CEO of FileFlo — compliance document intelligence. Reviewed June 13, 2026. FileFlo is a compliance document intelligence platform, not legal counsel, an A&P, or a repair station. Verify all recorder applicability, retention, correlation, and calibration requirements with a certificated A&P or IA, your repair station, and your FSDO.