Every charter pilot has done the mental math on the ramp: full fuel, four passengers, their bags, and the question of whether the airplane is still inside its envelope. Weight and balance is one of the few compliance areas where the regulation and the laws of physics point in exactly the same direction — fly an aircraft outside its certificated weight or CG limits and you have both a violation and a controllability problem.
But the part that trips operators up is not the per-flight arithmetic — it is the records. When was the aircraft last actually weighed? Is that empty-weight figure still the current one, or did last month's avionics upgrade quietly change it? Where is the load manifest from the flight an inspector is now asking about? The recordkeeping lives across a handful of CFR sections: 14 CFR §135.185 (the empty-weight and CG currency requirement), §135.63 (the load manifest), §43.9 and §43.5 (how an alteration gets documented), and §91.605 (transport category weight limits). Get the records wrong and you can be flying on superseded weight data, miss the 36-month reweigh window, or be unable to produce the load manifest an inspector requests.
This guide walks each layer in order: the currency requirement for the baseline empty weight and CG, the per-flight load manifest, the amendment process after a major alteration, and the weight limits that define the envelope. It is a companion to our master index of what records a Part 135 operator must keep and to the broader Part 91 aircraft records requirements guide.
Why Weight & Balance Records Are a Recordkeeping Problem, Not Just a Math Problem
Pilots are trained to compute weight and balance for every flight, and the computation itself is rarely the issue. The compliance exposure sits in the documents that feed and follow that computation: the baseline empty weight and CG the pilot starts from, and the load manifest the operator must produce afterward. Both are records the FAA can demand — and both have a way of going stale without anyone noticing.
Consider the two most common failure modes. First, the aircraft's weighing currency lapses: the last actual weighing was more than 36 calendar months ago, so under §135.185 the empty-weight figure on which every load calculation depends is no longer valid for Part 135 multiengine operations. Second, the empty weight silently changes: a cabin reconfiguration, a heavier avionics suite, new paint, or an STC kit shifts the empty weight and CG, but the W&B data the crew is using still reflects the pre-alteration airplane. Either way, the aircraft is flying on numbers that no longer describe it.
Three Layers, Three Different Rules
- Baseline currency — is the empty weight and CG current? §135.185
- Per-flight proof — was this departure loaded within limits? §135.63 load manifest
- Amendment after change — did the alteration get into the W&B and onto a Form 337? §43.9 / §43.5 / §91.417
The rest of this guide takes each layer in turn. If you only remember one thing: the aircraft's current weight and balance is whatever the most recent valid weighing or alteration says it is — and the records have to prove which figure that is.
The Currency Requirement: 14 CFR §135.185
14 CFR §135.185 is titled "Empty weight and center of gravity: Currency requirement," and its core rule is short:
"No person may operate a multiengine aircraft unless the current empty weight and center of gravity are calculated from values established by actual weighing of the aircraft within the preceding 36 calendar months."
— 14 CFR §135.185(a)
Three words carry the weight. "Multiengine" — the currency rule is written for multiengine aircraft, which is most of the Part 135 charter fleet. "Actual weighing" — the figure has to come from physically weighing the airplane, not from adding and subtracting paper weights since the last reweigh (that running computation is what the alteration process maintains between weighings; the 36-month rule forces a periodic re-baselining on the scales). "36 calendar months" — the window is calendar months, so a weighing in June 2026 carries the aircraft through the end of June 2029.
The Two §135.185 Exceptions
Newly certificated aircraft
The requirement does not apply to an aircraft issued an original airworthiness certificate within the preceding 36 calendar months — its manufacturer weighing is still inside the window. In practice this exception simply means the 36-month clock runs from original certification.
Approved weight and balance control system
The requirement does not apply to an aircraft operated under an approved weight and balance control system — a fleet-weight program documented in the operator's manual and operations specifications. Under such a program the carrier maintains current W&B through a control method (fleet-average empty weights, sample weighing, and rigorous equipment-change accounting) instead of weighing every individual tail on the 36-month cycle. This is the standard approach for larger fleets.
The reweigh date is an expiration date
The single most common §135.185 finding is a lapsed weighing: the last actual weighing was 37+ calendar months ago and nobody tracked the date. Because the consequence is that every subsequent load calculation rests on an out-of-currency empty weight, treat the next-reweigh date the same way you treat an inspection due date — surface it well before the 36-calendar-month window closes. This is exactly the kind of expiring document a Part 135 recordkeeping system should be flagging 90/60/30 days out.
What has to be on file from a weighing: the dated weighing record (scale readings, tare, and the computation), the resulting current empty weight and empty-weight center of gravity, the useful load, and the equipment list the empty weight reflects. Those figures are the starting point for every load manifest the operator prepares — which is the next layer.
The Per-Flight Proof: The §135.63 Load Manifest
14 CFR §135.63(c) requires the certificate holder to prepare a load manifest in duplicate before each takeoff for multiengine aircraft. The load manifest is where the empty-weight-and-CG baseline from §135.185 gets applied to a specific flight, a specific load, and a specific fuel state. It is the document that proves a given departure was inside the envelope.
Per §135.63(c), the load manifest must contain:
Number of passengers
The number of passengers carried on the flight.
Total weight of the loaded aircraft
The actual loaded weight for this departure — empty weight plus crew, passengers, cargo, and fuel.
Maximum allowable takeoff weight
The maximum allowable takeoff weight for that flight (which can be performance-limited below the certificated max for the conditions).
Center of gravity limits
The forward and aft CG limits applicable to the aircraft.
CG of the loaded aircraft
The center of gravity of the loaded aircraft — except that the actual CG need not be computed if the aircraft is loaded per an approved loading schedule that keeps it within limits, in which case a notation to that effect is entered.
Registration or flight number
The registration number of the aircraft or the flight number.
Origin and destination
The origin and destination of the flight.
Crew member identification
The identification of crew members and their crew position assignments.
Carry It and Keep It
Pilot in command carries a copy
The PIC must carry a copy of the completed load manifest to the destination. The duplicate stays with the certificate holder.
Retain at least 30 days
Per §135.63(d), the certificate holder keeps copies of completed load manifests for at least 30 days at its principal operations base, or another location used and approved by the Administrator.
The 30-day window is short — and inspectors know it
Unlike the multi-year permanent maintenance records, the load manifest retention floor is only 30 days. That makes it easy to under-retain: a manifest from a flight 45 days ago may already be gone if it was never filed properly. Operators who keep manifests well past 30 days do so for the same reasons they keep more than the minimum elsewhere — to answer a delayed FAA inquiry or to reconstruct a flight after an event. A consistent capture-and-index habit is the only thing that makes the 30-day floor a non-issue.
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Run the FAA Readiness Score — FreeAmendment After a Major Alteration: How the W&B Gets Updated
This is the layer operators most often get wrong, because it sits at the seam between maintenance and operations. When a major alteration changes the aircraft's empty weight or center of gravity — an interior reconfiguration, an avionics or equipment installation, a new paint scheme, an STC kit — the weight and balance must be recomputed, and the records have to reflect the change. The mechanism runs through Part 43.
§43.9(d) — Major alterations go on a form
Section 43.9 sets the content of every maintenance and alteration record entry (description of work, date completed, name of the person performing, and the signature, certificate number, and kind of certificate of the person approving the return to service). Critically, §43.9(d) provides that major repairs and major alterations must be entered on a form, and the form disposed of, in the manner prescribed in Appendix B to Part 43.
Appendix B — Execute FAA Form 337
Appendix B to Part 43 requires the person performing a major repair or major alteration to "execute FAA Form 337 at least in duplicate" and forward a copy to the FAA in the manner prescribed. (Certificated repair stations may use a customer work order in lieu of the form for certain major repairs only — a major alteration always requires Form 337.) Form 337 is the document that records the alteration — and the recomputed weight and balance data is part of what the alteration record must reflect.
§43.5 — No return to service until documented
Section 43.5 prohibits approving an aircraft for return to service after a major alteration unless the §43.9 (or §43.11) record entry has been made, the repair or alteration form prescribed by the Administrator has been executed, and — where the alteration changes the operating limitations or flight data — the aircraft flight manual is revised to reflect it under §91.9. A change to empty weight, CG, or useful load is exactly the kind of flight-data change that must propagate into the W&B section of the records and, where applicable, the AFM.
§91.417(a)(2)(vi) — The Form 337 is a life-of-aircraft record
Under §91.417(a)(2)(vi), a copy of each FAA Form 337 documenting a major alteration is part of the permanent records that must be retained for the life of the aircraft and transferred to the new owner on sale under §91.419. So the W&B amendment isn't a transient record — the Form 337 (and the revised weight and balance data behind it) travels with the airplane forever. See our full §43.9 maintenance-record entry guide for the entry-content details.
The trap: flying on superseded weight data
The failure mode here is subtle. The alteration gets done, the Form 337 gets executed, the airplane gets returned to service — but the current weight and balance figures the crew uses are never updated, so the cockpit W&B reflects the pre-alteration airplane. Now every load manifest is computed from a stale empty weight. The fix is procedural: a major alteration that touches weight or CG must produce a new empty weight, a new empty-weight CG, an updated useful load, and a revised equipment list — and those revised figures must reach whoever computes the load manifest. The recomputed W&B is the current W&B the moment the aircraft is returned to service.
One clarification worth making: §43.5 and §43.9 don't use the phrase "weight and balance" in their operative text — they govern the record entry and the form for an alteration generally. The reason a major alteration drives a W&B amendment is that changing empty weight or CG is a change to the aircraft's flight data, which §43.5 requires to be reflected, and the recomputation is standard airworthiness practice documented through the Form 337 the alteration already requires.
The Envelope Itself: Weight Limits and §91.605
The currency rule (§135.185) and the load manifest (§135.63) keep the aircraft's current weight and CG documented and applied — but the limits the manifest must keep the flight inside come from the aircraft's certification basis. For most airplanes those limits are the maximum weights and CG range in the type certificate data sheet and the approved Airplane Flight Manual. For transport category airplanes, a dedicated operating rule layers on top.
14 CFR §91.605 — Transport Category Civil Airplane Weight Limitations
Section 91.605 prohibits taking off a transport category airplane unless its operation stays within certificated weight limits for the conditions. Under §91.605(a) — which applies to transport category airplanes other than turbine-engine-powered airplanes certificated after September 30, 1958 — no person may take off such an airplane unless:
- The takeoff weight does not exceed the authorized maximum takeoff weight for the elevation of the airport of takeoff
- The elevation of the takeoff airport is within the altitude range for which maximum takeoff weights have been determined
- Normal consumption of fuel and oil in flight to the airport of intended landing will leave a weight on arrival not in excess of the authorized maximum landing weight for the elevation of that airport
- The elevations of the destination and alternate airports are within the altitude range for which the maximum landing weights have been determined
Summarized from 14 CFR §91.605(a). Turbine-powered transport category airplanes certificated after September 30, 1958 are excluded from §91.605(a) and are instead governed by the AFM-based limits of §91.605(b)–(c).
The takeaway for a charter operator flying a transport category airplane: the maximum allowable takeoff weight you write on the §135.63 load manifest is not a single fixed number — it is the lower of the certificated structural limit and the performance-limited weight for the airport elevation, temperature, and runway available. The load manifest's "maximum allowable takeoff weight for that flight" field is where §91.605 and the aircraft's performance data meet the day's actual loading.
And before every flight: §91.103 preflight action
14 CFR §91.103 requires the pilot in command, before beginning a flight, to become familiar with all available information concerning that flight — including, for any flight, runway lengths at airports of intended use and the takeoff and landing distance data from the approved Airplane Flight Manual (or other reliable information appropriate to the aircraft, accounting for airport elevation, runway slope, aircraft gross weight, wind, and temperature). Gross weight — which depends on the current W&B and the day's load — is a direct §91.103 preflight input, which is one more reason the underlying weight figures have to be current and correct.
The Weight & Balance Records Checklist
Pulling the layers together, here is what a complete weight-and-balance records picture looks like for a Part 135 multiengine operation. An inspector reviewing W&B will be looking for each of these — and so should you, before they do.
1. Current Empty Weight & CG (§135.185)
- A dated weighing record from an actual weighing within the preceding 36 calendar months
- The computed current empty weight and empty-weight center of gravity derived from that weighing
- The current useful load and the equipment list the empty weight reflects
- OR documentation that the aircraft is operated under an approved weight and balance control system (manual reference + ops spec)
- The next-reweigh due date tracked so it surfaces before the 36-calendar-month window closes
2. Load Manifests (§135.63)
- A completed load manifest prepared in duplicate before each takeoff
- Total loaded weight, maximum allowable takeoff weight, CG limits, and loaded CG (or approved-loading-schedule notation)
- Aircraft registration or flight number, origin and destination, passenger count, and identification of crew members with their crew position assignments
- PIC carried a copy to destination; certificate holder retains completed manifests at least 30 days at the principal operations base
3. Alteration Records (§43.9 / §43.5 / §91.417)
- An FAA Form 337 for every major alteration that changed empty weight or CG (executed at least in duplicate per Appendix B)
- The recomputed empty weight, empty-weight CG, useful load, and revised equipment list resulting from each alteration
- Aircraft Flight Manual revised where the alteration changed operating limitations or flight data (§43.5 / §91.9)
- All Form 337 copies retained for the life of the aircraft and transferred with the aircraft on sale (§91.417(a)(2)(vi) / §91.419)
- Confirmation the revised W&B figures reached whoever computes the load manifest — no flying on superseded data
4. Weight Limits & Performance Data
- Type certificate data sheet / AFM maximum weights and CG range for the specific aircraft
- For transport category airplanes: §91.605 takeoff/landing weight limits applied to airport elevation and conditions
- Takeoff and landing distance data used for the §91.103 preflight determination at the day's gross weight
How FileFlo Sits in the Weight & Balance Records Stack
FileFlo is a compliance document intelligence platform — a read-only proof layer that sits alongside your existing weight-and-balance and maintenance-tracking workflow and keeps the documents audit-ready. It classifies 600+ document types against the governing CFR section, so a weighing record gets tagged to §135.185, a Form 337 to the alteration record set, and a load manifest to §135.63. It tracks expirations — so a §135.185 36-calendar-month reweigh due date shows up 90/60/30 days out — and generates inspector-format audit binders on demand.
FileFlo does not compute your weight and balance, run your loading software, replace your DOM or A&P, or substitute for your maintenance-tracking system. It does not file your Form 337 or perform the weighing. It keeps the documents that prove your weight-and-balance compliance — the weighing record, the equipment list, the Form 337s, the retained load manifests — organized, indexed against the relevant CFR, and ready for an FAA inspector or a buyer's pre-purchase review.
Related Aviation Compliance Guides
What Records Must a Part 135 Operator Keep?
The master index of every Part 135 record, CFR cite, and retention period
Part 91 Aircraft Records Requirements
Permanent vs temporary records and the §91.417 / §91.419 framework
§43.9 Maintenance Record Entry Requirements
What every maintenance and alteration entry must contain
Part 91.409 Inspection Requirements
Annual, 100-hour, progressive, and AAIP inspection records
Airworthiness Directive Compliance Records
How Part 39 AD tracking works and what gets operators cited
Prepare for a Part 135 FAA Surveillance Audit
What inspectors ask for and how to be ready
Part 135 Pilot Records Required by the FAA
The §135.63(a)(4) airman and crewmember file requirements
FAA Part 135 SMS — May 28, 2027 Deadline
The Safety Management System rule now covering all Part 135
Frequently Asked Questions
What does 14 CFR §135.185 require for aircraft weight and balance?
14 CFR §135.185 — titled "Empty weight and center of gravity: Currency requirement" — provides that no person may operate a multiengine aircraft under Part 135 unless the current empty weight and center of gravity are calculated from values established by actual weighing of the aircraft within the preceding 36 calendar months. There are two exceptions: (1) aircraft issued an original airworthiness certificate within the preceding 36 calendar months, and (2) aircraft operated under a weight and balance system approved in the certificate holder's operations specifications. In plain terms: the multiengine aircraft you fly for hire must have been physically weighed within the last 36 calendar months, and the weighing record plus the resulting empty-weight-and-CG figures must be on file unless you are running an FAA-approved fleet weight control program.
How often must a Part 135 aircraft actually be weighed?
Under 14 CFR §135.185, a multiengine Part 135 aircraft must have its current empty weight and center of gravity calculated from an actual weighing performed within the preceding 36 calendar months — so the practical interval is every 36 calendar months unless an exception applies. The 36-month clock restarts each time the aircraft is actually weighed. The first exception covers an aircraft issued an original airworthiness certificate within the preceding 36 calendar months, because its manufacturer weighing is still current. The second exception covers aircraft operated under an approved weight and balance control system — a fleet-weight program in the operations specifications and manual that lets a carrier use a fleet average and component-change accounting instead of weighing each tail on the 36-month cycle. If you are not on an approved control program, plan the reweigh before the 36-calendar-month window closes.
What is a load manifest and what must it contain under §135.63?
A load manifest is the per-flight loading record required by 14 CFR §135.63(c) for multiengine aircraft. The certificate holder must prepare a load manifest in duplicate before each takeoff, and it must contain: the number of passengers; the total weight of the loaded aircraft; the maximum allowable takeoff weight for that flight; the center of gravity limits; the center of gravity of the loaded aircraft (except that the actual CG need not be computed if the aircraft is loaded according to an approved loading schedule that ensures the CG is within limits, in which case an entry to that effect is made on the manifest); the registration number of the aircraft or flight number; the origin and destination; and the identification of crew members and their crew position assignments. The pilot in command must carry a copy to the destination, and the certificate holder must keep copies of completed load manifests for at least 30 days at its principal operations base (or another approved location). The load manifest is where the empty-weight-and-CG figures from §135.185 get applied to a specific flight — it is the proof that this departure was loaded within limits.
How is weight and balance documentation amended after a major alteration?
When a major alteration changes an aircraft's empty weight or center of gravity — an interior reconfiguration, an avionics or equipment installation, a paint job, an STC modification — the weight and balance must be recomputed and the records updated. The mechanism runs through 14 CFR §43.9 and §43.5: under §43.9(d), major alterations must be entered on a form and disposed of per Appendix B to Part 43, and Appendix B requires the person performing the work to "execute FAA Form 337 at least in duplicate." Section §43.5 prohibits approving the aircraft for return to service after a major alteration until that record entry has been made and, where the alteration changes operating limitations or flight data, the aircraft flight manual is revised per §91.9. The revised weight and balance data (new empty weight, new empty-weight CG, new useful load, and an updated equipment list) is part of the records that must reflect the alteration. Under §91.417(a)(2)(vi), a copy of each FAA Form 337 for a major alteration is a life-of-aircraft record that transfers with the aircraft on sale. The headline rule for operators: after any major alteration, the aircraft's current weight and balance is the new computed figure — not the old one — and flying on superseded W&B data is an airworthiness problem.
Does a §135.185 weighing reset the 36-month clock, and what about an approved control program?
Yes — each actual weighing of the aircraft restarts the 36-calendar-month currency window under §135.185. So an aircraft weighed in June 2026 is current until the end of June 2029 (36 calendar months), provided no intervening major alteration invalidates the figures. The alternative to repeated weighing is the §135.185(b) exception for an aircraft operated under an approved weight and balance control system. Under such a program — documented in the operator's manual and operations specifications — the carrier maintains the fleet's weight and balance through a control method (fleet-average empty weights, mandatory weighing of a sample, and meticulous equipment-change accounting) rather than weighing each individual aircraft every 36 months. The approved control program is the standard approach for larger fleets; the 36-month physical reweigh is the default for operators without one. Either way, the records have to show how the current empty weight and CG were derived.
What is the difference between §135.185, §91.605, and the load manifest?
These three address different layers. 14 CFR §135.185 governs the currency of the aircraft's baseline empty weight and CG for Part 135 multiengine operations — the 36-calendar-month weighing requirement (or approved control program). 14 CFR §91.605 sets transport category civil airplane weight limitations — under §91.605(a), which applies to transport category airplanes other than turbine-powered airplanes certificated after September 30, 1958, takeoff is prohibited unless the takeoff weight does not exceed the authorized maximum for the takeoff-airport elevation, normal fuel and oil consumption in flight to the airport of intended landing will leave a weight on arrival not in excess of the authorized maximum landing weight for that airport's elevation, and the airport elevations are within the altitude ranges for which the weights were determined; turbine transports certificated after that date operate under the AFM-based limits of §91.605(b)–(c) instead. The §135.63 load manifest is the per-flight application: it documents that a specific departure, with its specific passengers, cargo, and fuel, was within the aircraft's weight and CG envelope. Empty weight and CG (from §135.185) feed the load manifest (under §135.63), and the airplane's certificated weight limits (under §91.605 for transport category, or the type certificate / AFM limits for smaller airplanes) define the envelope the manifest must keep the flight inside.
Who is responsible for keeping aircraft weight and balance records current?
Responsibility splits between the operator and the maintenance provider, but the burden of having current records falls on the certificate holder and the registered owner/operator. Under §135.185, the operator may not fly a multiengine aircraft for hire without current empty-weight-and-CG figures, so the operator must ensure the aircraft is weighed on the 36-calendar-month cycle (or covered by an approved control program) and that the weighing record and computed figures are on file. The A&P or repair station that performs a major alteration makes the §43.9 record entry and executes the FAA Form 337 that documents the W&B change, and §43.5 bars the return to service until that is done — but it is the owner/operator who must preserve the Form 337 (a §91.417(a)(2) life-of-aircraft record) and keep the current W&B data with the aircraft. For each flight, the certificate holder prepares the §135.63 load manifest and the pilot in command carries a copy. A ramp inspector who finds superseded W&B data, a stale weighing date, or a missing load manifest is looking at the operator's recordkeeping, not the mechanic's.
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Written by Chad Griffith, Founder & CEO, FileFlo · Reviewed June 9, 2026 · Primary sources: 14 CFR §135.185, §135.63, §91.605, §91.103, §43.9, §43.5, Appendix B to Part 43, §91.417, §91.419