Direct Answer
Adding an aircraft to a Part 135 certificate means satisfying 14 CFR §135.25 (U.S. registration, a current airworthiness certificate, airworthy condition, and exclusive use or a qualifying written agreement), passing an FAA conformity review — a records review plus a physical inspection — and receiving an operations specifications amendment under 14 CFR §119.51 that adds the tail to your aircraft authorization, carried in practice on the OpSpec D085 aircraft listing.
The amendment application must generally be filed at least 15 days before the proposed effective date — 90 days if the aircraft is a type not before proven in air carrier or commercial operator operations, which can also trigger proving or validation tests under 14 CFR §135.145. The conformity process itself is FAA practice carried out under internal guidance (FAA Order 8900.1), not a CFR checklist — but the records it reviews are all CFR-required.
Until the amendment is issued, the aircraft is not part of your authorized fleet: 14 CFR §119.5(g) prohibits operating as a direct air carrier or commercial operator without, or in violation of, an appropriate certificate and appropriate operations specifications. The fastest adds are the ones where the records package — registration, airworthiness certificate, AD status, life-limited parts status, inspection status, Form 337s, weight and balance, and the lease or exclusive-use agreement — is complete and internally consistent on day one.
Why the Ramp Is Not the Finish Line
Operators who are new to fleet growth tend to treat the aircraft purchase as the hard part and the FAA paperwork as a formality. The FAA sees it the other way around. Your certificate authorizes an envelope of operations, and your operations specifications define that envelope down to the individual airframe. A new tail is a change to the envelope — so the FAA verifies, before it signs anything, that the specific aircraft conforms to its type design, that its history is documented, that it is equipped for the operations you intend, and that it has been absorbed into your inspection program, your manuals, your weight-and-balance control, and your MEL. That verification runs on documents. The operators who add aircraft in weeks rather than months are not the ones with the best lawyers — they are the ones whose records package survives first contact with the FSDO.
This article walks the full sequence: the regulatory floor in §135.25, where the aircraft lands in your OpSpecs (and what D085 actually is), the §119.51 amendment clock, what the conformity inspection covers, and — the heart of it — the records package the FSDO reviews, document by document. For the broader recordkeeping picture behind all of this, start with what records a Part 135 operator must keep.
The §135.25 Floor: What Every Part 135 Aircraft Must Be
14 CFR §135.25(a) sets the entry test. No certificate holder may operate an aircraft under Part 135 unless that aircraft, in the rule's words, "Is registered as a civil aircraft of the United States and carries an appropriate and current airworthiness certificate issued under this chapter" and "Is in an airworthy condition and meets the applicable airworthiness requirements of this chapter, including those relating to identification and equipment." Three separate proofs hide inside those two clauses: an effective registration, a current airworthiness certificate, and a demonstrable airworthy condition — including the identification (data plate, registration markings) and equipment requirements that apply to the kind of operation.
Effective U.S. registration
The Certificate of Aircraft Registration must be effective — and registration now runs on a renewal clock. Under 14 CFR §47.40, a Certificate of Aircraft Registration issued in accordance with §47.31 expires seven years after the last day of the month in which it is issued. A freshly purchased aircraft mid-re-registration is a common day-one snag: until the registration is effective, §135.25(a)(1) is not met.
Current airworthiness certificate — aboard and displayed
The airworthiness certificate must be appropriate and current, and under 14 CFR §91.203 it must be in the aircraft and displayed at the cabin or cockpit entrance so it is legible to passengers or crew. The certificate, the registration, and the rest of the onboard document set are covered in detail in the ARROW documents guide linked below.
Airworthy condition, identification, and equipment
Airworthy condition is proven through the maintenance status records — inspection status, AD status, life-limited parts — reviewed in the records package below. Identification means the data plate and registration markings match the paperwork. Equipment means the aircraft actually carries what the kinds of operations you intend require (IFR, passenger-carrying, and any special authorizations).
Exclusive use and the written agreement — §135.25(b) and (c)
Paragraph (b) adds a fleet-level requirement that matters most to operators who fly other people's aircraft. Each certificate holder must have the exclusive use of at least one aircraft that meets the requirements for at least one kind of operation authorized in its operations specifications — and for each kind of operation for which it does not have exclusive use of an aircraft, it must have at least one qualifying aircraft available under a written agreement that includes arrangements for performing required maintenance. Paragraph (c) then defines the term: a person has exclusive use when it has the "sole possession, control, and use of it for flight, as owner, or has a written agreement (including arrangements for performing required maintenance), in effect when the aircraft is operated, giving the person that possession, control, and use for at least 6 consecutive months."
That definition is why the lease or use agreement for a managed or chartered-in aircraft is a compliance record, not just a business contract. The FSDO will read it — for the 6-consecutive-month term, for the maintenance arrangements, and for whether possession, control, and use actually sit with the certificate holder. Who controls the aircraft connects directly to the larger question of operational control in Part 135 — the FAA's sustained enforcement focus on certificate holders lending their authority to flights they do not actually control. Paragraph (d) of §135.25 is a narrow carve-out permitting certain foreign-registered, leased aircraft under specified conditions, including filing the agreement with the FAA Aircraft Registry — a special case most operators never touch.
The agreement is part of the records package
Operators assembling an add-an-aircraft package routinely include the airworthiness records and forget the ownership and use documents. If the aircraft is leased or managed, expect the FSDO to ask for the written agreement and check it against §135.25(b)–(c): term, maintenance arrangements, and who holds possession, control, and use. An agreement that gives the owner veto power over maintenance scheduling, or that runs month-to-month, invites exactly the questions that stall an add.
Where the Aircraft Lives in Your OpSpecs: §119.49 and D085
The aircraft side of your operations specifications has two layers — what the CFR requires the OpSpecs to contain, and how the FAA's standardized template organizes it. The CFR layer is 14 CFR §119.49. For on-demand operations, §119.49(c) requires the OpSpecs to contain, among other items, the "Category and class of aircraft that may be used in those operations"; the "Type of aircraft, registration markings, and serial number of each aircraft that is subject to an airworthiness maintenance program required by § 135.411(a)(2)" — the 10-or-more-passenger-seat CAMP fleet — and the "Registration markings of each aircraft that is to be inspected under an approved aircraft inspection program under § 135.419," a listing §135.419(h) independently requires. For commuter operations, §119.49(a)(4) goes further: the type, registration markings, and serial numbers of each aircraft authorized for use.
The template layer is where D085 comes in. In the FAA's standardized operations specifications system — the lettered A/B/C/D paragraph structure described in FAA Order 8900.1 and generated through the agency's automated OpSpecs platform — the aircraft listing is carried in the D-series, commonly as paragraph D085. In practice, your certificate-holding office enters each aircraft's data into the system and issues a revised D085 enumerating every individual aircraft authorized under the certificate, typically by registration number, serial number, and make/model/series. The listing is public-facing, too: the FAA publishes its list of legal Part 135 operators and their aircraft compiled from OpSpec D085 data. The paragraph number is an administrative convention rather than a regulation — but the revision the FAA issues against it is binding, because operating in violation of your OpSpecs is a violation in its own right.
A third record sits alongside both layers: 14 CFR §135.63(a)(3) requires every certificate holder to keep at its principal business office, available for FAA inspection, "A current list of the aircraft used or available for use in operations under this part and the operations for which each is equipped." When you add a tail, that list must change the same day the amendment is effective — it is one of the first things an inspector can cross-check against the issued D085, and a mismatch is a finding that costs nothing to avoid.
Do not fly the tail before the amendment is effective
Under 14 CFR §119.5(g), no person may operate as a direct air carrier or commercial operator without, or in violation of, an appropriate certificate and appropriate operations specifications — and §119.5(l) separately prohibits operating an aircraft under Part 135 in violation of the operating certificate or appropriate OpSpecs. A revenue flight in an aircraft that is not yet on your aircraft authorization is one of the cleanest violations an inspector can document, because the comparison is binary: the flight log shows the tail flew, and the OpSpecs revision shows it was not authorized. Position the closing, the insurance, and the customer commitments around the amendment date — not the other way around.
For how the rest of the OpSpecs paragraph system works — the A/B/C/D series, amendments, and the documents that prove your authorization envelope — see the companion guide to operations specifications explained.
The §119.51 Amendment Clock: 15 Days or 90
Adding an aircraft is, mechanically, an amendment of your operations specifications under 14 CFR §119.51. The Administrator may amend OpSpecs if the certificate holder applies and the Administrator determines that safety in air commerce and the public interest allow it. For operator-requested amendments, the rule sets two minimum filing windows, and which one applies depends on what kind of add this is.
Same-type add: 15-day minimum
Adding another aircraft of a make and model already proven on your certificate falls in the catch-all: the application must be filed at least 15 days before the date proposed for the amendment to become effective. In practice these adds move on the FSDO's schedule, not the rule's minimum — what you control is whether the records package and the conformity inspection go through on the first pass.
- No new training program revision is typically needed for an identical type already in the fleet.
- The existing MEL for the make/model usually extends to the new serial number, adjusted for configuration differences.
- The records review and conformity inspection still happen — same-type does not mean no-inspection.
New-type introduction: 90-day minimum
The 90-day filing window applies to the heavyweight cases listed in §119.51(c) — mergers, acquisitions requiring an additional showing of safety, changes in the kind of operation, post-bankruptcy resumption, and the one that matters here: the "Initial introduction of aircraft not before proven for use in air carrier or commercial operator operations." A first-of-type add is a project, not a filing:
- Possible proving or validation tests under §135.145 (next paragraph).
- Training program revision for the new type — see training program recordkeeping.
- Manual, checklist, MEL, and weight-and-balance program updates — see the GOM/GMM requirements.
Proving and validation tests — §135.145
14 CFR §135.145 is the reason a first-of-type add can involve flying before you are allowed to earn revenue with the aircraft. Paragraph (a) prohibits operating an aircraft — other than a turbojet — for which two pilots are required for VFR operations unless the certificate holder has previously proved such an aircraft in Part 135 operations in at least 25 hours of proving tests acceptable to the Administrator, with night and instrument-approach elements where those authorizations are sought. Paragraph (b) imposes the parallel 25-hour proving requirement for turbojet airplanes not previously proven. Paragraph (c) is blunt about who rides along: "No certificate holder may carry passengers in an aircraft during proving tests, except those needed to make the tests and those designated by the Administrator to observe the tests."
Validation testing is the related, lighter-weight track. Under §135.145(d), validation tests are required for several authorizations, the first being "The addition of an aircraft for which two pilots are required for operations under VFR or a turbojet airplane, if that aircraft or an aircraft of the same make or similar design has not been previously proved or validated in operations under this part" — plus operations outside U.S. airspace, Class II navigation authorizations, and special performance or operational authorizations. Paragraph (e) softens the burden where it can: the tests must use methods acceptable to the Administrator, and actual flights may not be required when the applicant can demonstrate competence by other means. Paragraph (f) allows proving and validation tests to run simultaneously when appropriate.
The practical read: a single-pilot piston already common in Part 135 service triggers none of this; a turbojet or two-pilot type your certificate has never proven triggers some or all of it, and the FAA — not the operator — makes the call on scope. Every proving and validation hour generates its own records trail: test plans, flight logs, and the FAA's acceptance, all of which become part of the certificate's permanent history.
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The Conformity Inspection: What the FSDO Actually Verifies
Here is the part the CFR does not script. There is no section of Part 135 titled conformity inspection — the process is FAA certification and surveillance practice, carried out by the aviation safety inspectors assigned to your certificate under the agency's internal guidance in FAA Order 8900.1. Its purpose, as the FAA describes it in its airline-certification materials, is to verify that the specific aircraft conforms to its type design and is configured — bridged — into your approved programs and operations before the OpSpecs amendment is issued. Operators are commonly asked to support it with a written statement that the aircraft and its equipment conform to the requirements of §135.25: registration, current airworthiness certification, identification, and airworthy condition. The regulatory hooks are all real CFR — §135.25, §119.49, §119.5 — but the sequence, the job aids, and the depth of review are practice, and they vary by office and by how novel the aircraft is to your certificate.
The records half
Inspectors work through the aircraft's documented history and current status — the full package detailed in the next section. FAA Order 8900.1 contains dedicated guidance for inspecting the maintenance records of nine-or-less operators and of CAMP operators, and the questions track the status items the CFR requires you to keep: times, life-limited parts, overhauls, inspections, ADs, and major alterations.
This half fails on internal inconsistency more than on missing paper: a Form 337 describing an installation the equipment list does not show, an AD compliance entry citing a method that does not match the logbook, total-time arithmetic that does not reconcile across airframe and engine records.
The physical half
Inspectors then look at the aircraft itself and compare it to the paperwork: data plate and registration markings against the registration; installed configuration against the type certificate data sheet and the STC/field-approval trail in the 337s; required placards; and the equipment the kinds of operations you are requesting demand.
The classic finding is an aircraft that is airworthy but does not match its own records — an avionics swap nobody documented, or a documented alteration that was later removed. Conformity means the aircraft and the records describe the same machine.
Guidance, not regulation — confirm with your own FSDO
FAA Order 8900.1 and the standardized OpSpecs paragraph templates are internal FAA guidance and administrative conventions, revised over time — not CFR. The description here is an orientation to how the process typically runs, not a checklist you can hold your inspector to or be held to verbatim. Your Principal Operations Inspector and Principal Maintenance Inspector own the sequence for your certificate; ask them what their office expects in the package before you submit it.
Who is involved follows from what is being verified: the operations side of the FSDO or certificate management office handles the kinds-of-operations and OpSpecs questions, the airworthiness side handles the records review and physical conformity, and scheduling across both is — far more than the 15-day minimum in §119.51 — what actually sets your timeline. The single biggest accelerator available to the operator is a package that needs no second visit.
The Records Package the FSDO Reviews, Document by Document
Every item below is a record the CFR independently requires to exist — the conformity review simply reads them all at once, against each other and against the aircraft. For an aircraft coming onto the nine-or-less track, the status records live under 14 CFR §91.417; for a CAMP aircraft the parallel set lives under §135.439 — and per 14 CFR §91.401(b), §§91.405, 91.409, 91.411, 91.417, and 91.419 do not apply to an aircraft maintained under a continuous airworthiness maintenance program as provided in §135.411(a)(2). Either way, the substance the inspector wants is the same.
Registration and Airworthiness Certificates
§135.25(a) / §91.203 / §47.40What the FSDO is checking
The aircraft must be registered as a U.S. civil aircraft with an effective Certificate of Aircraft Registration — which under §47.40 expires seven years after the last day of the month in which it is issued — and must carry an appropriate, current airworthiness certificate, displayed per §91.203(b). Mid-sale re-registration gaps and certificates still showing the previous owner are the most common day-one defects in an add package.
How FileFlo tracks it
FileFlo classifies both certificates against the aircraft, tracks the registration expiration date, and flags the gap if a newly added tail is missing either document.
Maintenance Status Records — the §91.417(a)(2) Set
§91.417(a)(2)(i)–(vi) / §135.439(a)(2)What the FSDO is checking
The permanent status records that transfer with the aircraft: total time in service of the airframe, each engine, propeller, and rotor; the current status of life-limited parts of each airframe, engine, propeller, rotor, and appliance; time since last overhaul of items required to be overhauled on a specified time basis; the current inspection status, including time since the last inspection required by the inspection program the aircraft is maintained under; the current status of applicable ADs, including for each the method of compliance, the AD number, and revision date; and copies of the forms prescribed by §43.9(d) — FAA Form 337 — for each major alteration to the airframe and currently installed engines, rotors, propellers, and appliances. Under §91.417(b)(2), these records are retained and transferred with the aircraft when it is sold — so an aircraft arriving without them arrived broken.
How FileFlo tracks it
FileFlo classifies each status document — AD compliance records, life-limited parts status, overhaul records, 337s — indexes them to the tail, and surfaces what is missing from the set before the FSDO does.
Inspection Program Assignment
§135.411 / §91.409(e)–(f) / §135.419 / §135.421What the FSDO is checking
The package must show which inspection program the aircraft will be maintained under going forward. Nine-or-less aircraft run under parts 91 and 43 plus §§135.415, 135.417, 135.421, and 135.422 — with §135.421(a) requiring compliance with the manufacturer's recommended maintenance programs (or an approved program) for each engine, propeller, rotor, and required emergency equipment item, and §91.409(e)–(f) requiring large airplanes, turbojet and turbopropeller-powered multiengine airplanes, and turbine-powered rotorcraft to operate under a selected inspection program. An approved aircraft inspection program may be used under §135.419 — and §135.419(h) puts the registration number of each AAIP aircraft into the OpSpecs. Ten-or-more-seat aircraft go onto the CAMP under §135.411(a)(2). Bridging the new tail into the program — current with no overdue items at the time of the add — is the heart of the airworthiness review.
How FileFlo tracks it
FileFlo keeps the program documents, the bridging records, and each tail's inspection-status evidence classified and current — the proof layer for the program your maintenance provider executes.
Weight and Balance Records
§135.185 / §135.63What the FSDO is checking
For a multiengine aircraft, §135.185(a) requires that the current empty weight and center of gravity be calculated from values established by actual weighing within the preceding 36 calendar months — with exceptions in (b) for aircraft issued an original airworthiness certificate within the preceding 36 calendar months and aircraft operated under a weight-and-balance system approved in the operations specifications. An aircraft that has been sitting with a years-old weighing report is a conformity stopper that is cheap to fix before submission and expensive to discover during it.
How FileFlo tracks it
FileFlo classifies weighing reports and W&B documents per tail and tracks the 36-calendar-month clock so the reweigh happens before the deadline, not after the finding.
Lease / Exclusive-Use Agreement
§135.25(b)–(c)What the FSDO is checking
If the certificate holder does not own the aircraft, the written agreement giving it possession, control, and use — including arrangements for performing required maintenance — is part of the package, and the exclusive-use definition in §135.25(c) (at least 6 consecutive months) is the standard the fleet-level requirement is read against. Expect the FSDO to read the actual signed document, not a summary of it.
How FileFlo tracks it
FileFlo stores the executed agreement against the tail with its term dates tracked, so the 6-month horizon and renewal date are visible — and the document is retrievable the moment an inspector asks.
Minimum Equipment List
§135.179What the FSDO is checking
To dispatch with inoperative equipment, §135.179(a) requires that an approved Minimum Equipment List exists for that aircraft and that the responsible Flight Standards office has issued the certificate holder operations specifications authorizing operations in accordance with an approved MEL — an authorization carried in the OpSpecs (commonly as paragraph D095 in the FAA template). For a same-type add, the existing MEL is typically extended to the new serial number with configuration differences reconciled; for a new type, MEL development is one of the long poles in the 90-day case.
How FileFlo tracks it
FileFlo version-tracks the MEL and its OpSpecs authorization per aircraft, flagging the configuration-mismatch risk when a new serial number joins an existing make/model.
Equipment and Special-Authorization Evidence
§135.25(a)(2) / kind-of-operation rulesWhat the FSDO is checking
The §135.25(a)(2) airworthy-condition clause includes the requirements relating to identification and equipment — meaning the aircraft must demonstrably carry what the kinds of operations you are requesting require, from IFR equipment to any special-airspace capability. Where the operation depends on inspections or evidence with their own clocks — altimeter and transponder tests, ADS-B Out performance — the proof goes in the package.
How FileFlo tracks it
FileFlo tracks the equipment-evidence documents and their expirations per tail — the 24-calendar-month test records, equipment lists, and authorization letters that back the operations you sell.
Deep dives on the package contents: AD compliance records · life-limited parts records · engine & propeller overhaul time tracking · §43.9 maintenance record entries · weight & balance records · MEL/CDL records · ARROW documents · RVSM / §91.411–413 test records · ADS-B Out compliance records
Run the free FAA readiness check before the FSDO runs theirs
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After the Amendment: Keeping the New Tail Provable
The amendment date is when the compliance work changes shape, not when it ends. The day the revised aircraft listing is issued, a set of records obligations attaches to the new tail and never lets go — and several of them are exactly what the next surveillance visit will sample.
Update the §135.63(a)(3) aircraft list the same day
The current list of aircraft used or available for use — and the operations for which each is equipped — kept at your principal business office must reflect the add immediately. It is the cheapest cross-check an inspector has against the issued OpSpecs.
File the OpSpecs revision into your master set and reconcile your manuals
The amended aircraft listing is a new OpSpecs revision with a new effective date. Your master set must carry it, and any operating-manual excerpts that reference the fleet need to be reconciled — version drift between issued OpSpecs and manual excerpts is a classic surveillance finding.
Keep the status records current — they now have an audience
The §91.417(a)(2) (or §135.439(a)(2)) status set — times, life-limited parts, overhauls, inspection status, ADs, major alterations — must stay current for as long as the tail is on the certificate, and under §91.417(b)(2) it transfers with the aircraft when you eventually sell. The conformity review you just passed is the same review the buyer's FSDO will run.
Watch the recurring clocks the add just started
Registration renewal under the §47.40 seven-year cycle, the §135.185 36-calendar-month weighing for multiengine aircraft, recurring AD actions, inspection-program intervals, and any test-and-evidence cycles behind the operations the tail flies. Every one of these is a dated document with a failure mode of silence.
Fleet growth also scales every per-aircraft and per-pilot records obligation you already carry — from the part 91 aircraft records baseline to CAMP recordkeeping if the new tail puts you on the ten-or-more track, and onward into the safety-management obligations arriving with the Part 135 SMS deadline. One more aircraft is never just one more folder.
FileFlo is the proof layer, not the operational layer
FileFlo is a compliance document intelligence platform — it classifies, indexes, version-tracks, and surfaces expirations on the records that the add-an-aircraft process and everything after it run on. It does not submit OpSpecs applications, schedule or perform conformity inspections, run dispatch, execute your maintenance or inspection program, or interact with FAA systems. Your director of operations, director of maintenance, and your principal inspectors own the process; FileFlo keeps the resulting record — for the new tail and the whole fleet — complete, current, and retrievable the moment someone with a badge asks for it.
Frequently Asked Questions
What does 14 CFR §135.25 require before an aircraft can fly under Part 135?
Under 14 CFR §135.25(a), no certificate holder may operate an aircraft under Part 135 unless it is registered as a civil aircraft of the United States and carries an appropriate and current airworthiness certificate issued under 14 CFR, and is in an airworthy condition meeting the applicable airworthiness requirements of the chapter, including those relating to identification and equipment. Separately, §135.25(b) requires the certificate holder to have exclusive use of at least one aircraft that meets the requirements for at least one kind of operation authorized in its operations specifications — and, for each kind of operation where it lacks exclusive use, at least one qualifying aircraft available under a written agreement that includes arrangements for performing required maintenance. §135.25(c) defines exclusive use as sole possession, control, and use of the aircraft for flight, as owner, or under a written agreement in effect whenever the aircraft is operated that gives that possession, control, and use for at least 6 consecutive months. §135.25(d) is a narrow allowance for certain foreign-registered, leased aircraft under specified conditions.
Does every aircraft have to be listed in our operations specifications?
Read it as two layers. The CFR floor for on-demand operators is 14 CFR §119.49(c): OpSpecs must contain the category and class of aircraft that may be used, the type of aircraft, registration markings, and serial number of each aircraft subject to an airworthiness maintenance program required by §135.411(a)(2) — the 10-or-more-passenger-seat CAMP fleet — and the registration markings of each aircraft inspected under an approved aircraft inspection program under §135.419 (which §135.419(h) independently requires). For commuter operations, §119.49(a)(4) requires the type, registration markings, and serial numbers of each aircraft authorized for use. On top of that floor, standing FAA practice is to enumerate every individual aircraft operated under the certificate in the OpSpecs aircraft-listing paragraph — commonly D085 — maintained through the agency automated OpSpecs system. And 14 CFR §135.63(a)(3) separately requires you to keep, at your principal business office, a current list of the aircraft used or available for use in Part 135 operations and the operations for which each is equipped. Because §119.5(g) and (l) prohibit operating without, or in violation of, appropriate operations specifications, flying a tail before it appears in your aircraft authorization is treated as operating outside your authorized fleet.
What is OpSpec D085?
D085 is the paragraph the standardized FAA operations specifications template uses for the aircraft listing — the table that identifies each individual aircraft authorized for use under the certificate, typically by registration number, serial number, and make/model/series. It sits in the D-series (the maintenance and airworthiness side) of the OpSpecs, and the aircraft data behind it is entered and maintained in the FAA automated OpSpecs system by your certificate-holding office. The paragraph number itself is an FAA administrative convention described in FAA Order 8900.1, not a CFR section — the regulatory substance comes from 14 CFR §119.49, which prescribes the aircraft-related contents of OpSpecs, and §119.5, which makes operating in violation of OpSpecs a violation in its own right. When operators say a tail is on the D085, they mean the FAA has issued an OpSpecs revision that adds that specific aircraft to the certificate. The FAA even publishes its public list of legal Part 135 operators and their aircraft from OpSpec D085 data. Always confirm paragraph numbering and contents against your own issued OpSpecs and your assigned FAA office.
What is a conformity inspection, and which regulation requires it?
A conformity inspection is the FAA pre-addition verification that the specific aircraft you want to add actually matches what the paperwork says: that it conforms to its type design (including alterations documented by STC, field approval, and the Form 337 trail), is in condition for safe operation, carries the required certificates and markings, is equipped for the kinds of operations you intend, and has been bridged into your inspection program, manuals, weight-and-balance control, and MEL where applicable. The inspection process itself is not spelled out in a CFR section — it is FAA certification and surveillance practice, conducted by aviation safety inspectors at your Flight Standards office under internal guidance in FAA Order 8900.1. The regulatory hooks behind it are real, though: §135.25(a) requires the aircraft to be properly registered, certificated, and airworthy; §119.49 requires the OpSpecs aircraft authorizations to be accurate; and the FAA does not issue the amendment until its inspectors are satisfied. In practice the inspection has two halves — a records review of the aircraft history and status documents, and a physical inspection of the aircraft itself — and the records half is where most delays start.
How far in advance do we have to apply to add an aircraft?
The amendment mechanics live in 14 CFR §119.51. For operator-requested amendments, the application must generally be filed at least 15 days before the date proposed for the amendment to become effective. A 90-day minimum filing window applies instead to major changes — including the initial introduction of aircraft not before proven for use in air carrier or commercial operator operations, mergers, acquisitions of airline operational assets that require an additional showing of safety, changes in the kind of operation, and resumption of operations following a bankruptcy-related suspension. So adding another aircraft of a make and model already proven on your certificate is normally a 15-day-minimum filing, while introducing a never-before-proven type is a 90-day-minimum filing that may also trigger proving or validation tests under §135.145. Treat both numbers as regulatory minimums, not promises: the real calendar is driven by how quickly your FSDO can schedule the records review and conformity inspection — and by how clean your records package is when you hand it over.
Do we need proving or validation tests for the added aircraft?
Only when the aircraft is new ground for your certificate. Under 14 CFR §135.145(a), a certificate holder may not operate an aircraft (other than a turbojet) for which two pilots are required for VFR operations unless it has previously proved such an aircraft in Part 135 operations in at least 25 hours of proving tests acceptable to the Administrator; §135.145(b) imposes a parallel 25-hour proving requirement for turbojet airplanes not previously proven. During proving tests, §135.145(c) prohibits carrying passengers except those needed to make the tests and those designated by the Administrator to observe them. Validation testing under §135.145(d) is required for, among other things, the addition of an aircraft for which two pilots are required for operations under VFR or a turbojet airplane, if that aircraft or an aircraft of the same make or similar design has not been previously proved or validated in operations under this part — and for operations outside U.S. airspace, Class II navigation, and special performance or operational authorizations. Under §135.145(e) the tests must use methods acceptable to the Administrator, and actual flights may not be required where compliance can be demonstrated otherwise. Adding another tail of a make or similar design you already operate generally does not re-trigger testing — but that determination belongs to the FAA, not the operator.
Which maintenance and inspection program does the added aircraft go on?
It depends on the passenger seating configuration the aircraft is type certificated for, excluding any pilot seat. Under 14 CFR §135.411(a)(1), aircraft with nine passenger seats or less are maintained under parts 91 and 43 plus §§135.415, 135.417, 135.421, and 135.422 — meaning the part 91 inspection rules apply, an approved aircraft inspection program may be used under §135.419, and §135.421(a) requires compliance with the manufacturer recommended maintenance programs (or an Administrator-approved program) for each engine, propeller, rotor, and each required item of emergency equipment. For large airplanes, turbojet and turbopropeller-powered multiengine airplanes, and turbine-powered rotorcraft on the nine-or-less track, §91.409(e) and (f) require selecting an inspection program — such as a current manufacturer-recommended program — and sticking with it. Under §135.411(a)(2), aircraft type certificated for ten passenger seats or more must be maintained under a continuous airworthiness maintenance program (CAMP) built on §§135.415, 135.417, and 135.423 through 135.443, and §135.411(b) lets an operator elect that program for smaller aircraft too. One structural trap: per §91.401(b), the part 91 maintenance sections §§91.405, 91.409, 91.411, 91.417, and 91.419 do not apply to an aircraft maintained under a CAMP as provided in §135.411(a)(2) — a CAMP tail keeps its records under §135.439 instead of §91.417.
Does FileFlo file the OpSpecs amendment or run the conformity inspection?
No. FileFlo is a compliance document intelligence platform — it classifies, indexes, version-tracks, and surfaces expirations on the records that the add-an-aircraft process runs on: the registration and airworthiness certificates, the airworthiness directive status, life-limited parts status, inspection status, Form 337s, weight-and-balance reports, lease and exclusive-use agreements, MEL, and the OpSpecs revisions themselves. It does not submit applications to the FAA, communicate with your principal inspectors, schedule or perform conformity inspections, run your maintenance tracking, or amend the D085. Those belong to your director of operations, director of maintenance, and the FAA. What FileFlo does is make the records half of conformity fast and provable: when the FSDO asks for the package, every document is classified, current, and retrievable in one place — and after the add, the expirations that keep that tail legal are tracked before they lapse.
Make the records half of conformity the easy half
FileFlo classifies and tracks the documents an aircraft add runs on — registration and airworthiness certificates, AD status, life-limited parts, overhaul times, 337s, weight and balance, lease agreements, MELs, and the OpSpecs revisions that carry your D085 — then keeps every expiration on watch after the tail is flying. AI document classification. 600+ document types. One-click audit binder for the FSDO. Starter at $89/mo, Professional at $299/mo.
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Reviewed by Chad Griffith, Founder, FileFlo — compliance document intelligence. Last reviewed June 10, 2026. Regulatory citations verified against the Cornell Legal Information Institute eCFR (14 CFR §§135.25, 119.49, 119.51, 119.5, 135.63, 135.145, 135.179, 135.185, 135.411, 135.419, 135.421, 135.439, 91.203, 91.401, 91.409, 91.417, and 47.40) as of the publication date. Descriptions of the conformity inspection process, FAA Order 8900.1, and OpSpec paragraph conventions (D085, D095) are an orientation to FAA practice and guidance, not CFR — confirm specifics with your assigned FSDO and your own issued operations specifications.