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Operating empty weight
Operating empty weight
Operating empty weight
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Empty weight (EW) is the sum of the ‘as built’ manufacturer's empty weight (MEW), plus any standard items (SI) plus any operator items (OI), EW = MEW + SI + OI. The EW is calculated for each aircraft series and each unique configuration of an aircraft and is confirmed by periodically weighing it. The "Operating empty weight" (OEW) is the sum of the empty weight and the crew plus their baggage.

Standard items include all structural modification or configuration orders that may have altered the MEW, including all fluids necessary for operation such as engine oil, engine coolant, water, hydraulic fluid and unusable fuel. Operator items include fixed, optional equipment added by the operator for service reasons.

The weight added to the aircraft above its OEW for a given flight is variable and includes fuel for the flight and the cargo. Cargo depends upon the type of aircraft; i.e., passengers plus baggage for a transport or commuter airplane, materiel for a cargo airplane, stores for fighters/bombers and service loads such as meals and beverages. Fuel and cargo weights may alter the centre of gravity and flight performance, and require careful calculation before each flight.

Aircraft purchase price by type is a close linear function of EW.[1][2]

See also

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References

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Operating empty weight

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Operating empty weight (OEW), also referred to as operational empty weight, is the total of an prepared for flight operations, consisting of the basic empty weight—which includes the , engines, systems, furnishings, unusable , full operating fluids (such as oil and ), and fixed equipment—plus the required flight , their baggage and personal equipment, and standard operational items like supplies, potable , manuals, and gear, while excluding usable and (passengers, baggage, and ). This weight serves as the foundational baseline in aircraft weight and balance calculations, enabling operators to determine allowable payload, zero-fuel weight, and overall takeoff gross weight while ensuring adherence to certification limits set by authorities such as the Federal Aviation Administration (FAA). Variations in OEW arise from aircraft configuration, optional equipment installations, and operator-specific additions, necessitating periodic weighing and updates to the aircraft's records for accuracy. Precise management of OEW is critical for flight safety, as it directly influences performance parameters including climb capability, cruise efficiency, and landing requirements; exceeding derived weight limits based on an inaccurate OEW can compromise structural integrity and handling characteristics. In commercial aviation, fleet operating empty weight (FOEW) represents an averaged OEW across similar aircraft, facilitating standardized planning for airlines.

Fundamentals

Definition

Operating empty weight (OEW), also known as operational empty weight, is the total mass of an in a condition ready for flight operations, encompassing the manufacturer's empty weight, all fixed installations and operational equipment, unusable and other propulsion fluids, full operating fluids such as engine oil and , the minimum required along with their and personal items, plus standard operational items such as supplies, potable , manuals, and passenger service equipment. This excludes usable , passengers, , cargo, and any non-standard or optional items not essential to basic operations. The definition aligns with FAA guidance for transport-category under 14 CFR Part 25, as elaborated in advisory circulars, where OEW provides a consistent baseline for and assessments. In practice, OEW establishes the foundational weight from which variable loads like and are added during , representing the aircraft's state as equipped for typical passenger or cargo missions without those elements. It ensures compliance with weight and balance requirements by for all mandatory operational elements, thereby supporting accurate calculations of takeoff, landing, and cruise performance. The term OEW was formalized in post-1940s regulations, evolving from under the Civil Aeronautics Administration and later codified by the established in 1958, to standardize weight terminology and enhance safety through uniform control procedures. Further refinement occurred via advisory circulars like AC 120-27 series starting in the 1960s and General Aviation Manufacturers Association (GAMA) Specification No. 1 in 1976, which harmonized definitions across manufacturers for consistent application in certification and operations.

Components

The operating empty weight (OEW) encompasses the 's structural elements, which form its fixed skeleton and include the , wings, , tail assembly, and . These components provide the foundational framework essential for the 's integrity and aerodynamic performance. The powerplant and associated systems contribute significantly to the OEW, comprising engines, propellers (for propeller-driven ), auxiliary power units, and related equipment such as fuel pumps. Only unusable fuel— the residual amount that cannot be drained from the tanks—is included in this category, while usable fuel is excluded. Fixed equipment forms another core part of the OEW, including , instruments, systems, emergency equipment like life vests and fire extinguishers, and interior furnishings such as passenger seats, galleys, and overhead bins. These items are permanently installed or standard for operational readiness and are weighed as part of the aircraft's baseline configuration. Operational fluids are fully accounted for in the OEW to reflect the aircraft's ready-to-fly state, including full engine oil, for control systems, coolants, and the aforementioned unusable . These fluids ensure system functionality without contributing to consumable loads during flight. Standard operational items, such as catering supplies, potable water, manuals, and additional passenger service equipment, are also included to represent the configured for typical missions. The OEW also incorporates the weight of the minimum flight crew—typically a pilot and co-pilot for multi-crew —along with their and personal items as determined by operator standards. This accounts for the essential personnel required for basic operations.

Basic Empty Weight

Basic empty weight (BEW), also known as manufacturer’s empty weight in some contexts, represents the total mass of an in its standard configuration, encompassing the , engines, fixed , optional or special installations, unusable fuel, and full operating fluids such as engine oil and , while excluding , passengers, , usable fuel, and any . This weight serves as the foundational baseline for manufacturers when certifying and documenting the empty condition of the prior to operational additions. In contrast to operating empty weight (OEW), which incorporates the and sometimes to reflect a ready-to-fly state, BEW omits these human-related elements, yielding a lower value that emphasizes the aircraft's inherent structure and systems for design and regulatory purposes. This distinction ensures BEW remains a fixed, manufacturer-provided figure, facilitating consistent comparisons across models without variability from operational staffing. For instance, in a light aircraft like the Skyhawk, the basic empty weight typically ranges from 1,600 to 1,800 pounds, depending on specific optional equipment, and acts as the initial reference point for pilots when computing total takeoff weight by adding fuel, occupants, and cargo. The standardization of basic empty weight under the General Aviation Manufacturers Association (GAMA) specifications occurred in the 1970s, promoting uniformity in weight reporting for aircraft and aligning with evolving (FAA) guidelines to enhance and processes.

Zero Fuel Weight

Zero fuel weight (ZFW) refers to the total weight of an aircraft including its operating empty weight plus any payload—such as passengers, cargo, and catering—but excluding all usable fuel and other specified usable fluids. This weight represents the aircraft's configuration just prior to fuel loading for a flight, serving as a critical limit in weight and balance computations. The maximum zero fuel weight (MZFW) is the highest permissible value for this configuration, determined by the aircraft's design specifications and certified limits. ZFW is directly related to operating empty weight, calculated as ZFW = OEW + , where the operating empty weight provides the foundational mass upon which is added. This relationship ensures that payload capacities are computed starting from the verified OEW, allowing operators to maximize revenue loads while adhering to structural constraints. The primary structural purpose of the ZFW limit is to protect the aircraft's wing spars from excessive bending stress caused by heavy loads without the counterbalancing effect of in the wings. By capping the weight forward of the wings, the MZFW prevents overload on the structure during ground operations or , where is not yet present to distribute loads aft. For commercial aircraft like the series, typical MZFW values range from approximately 113,500 pounds for smaller variants such as the 737-700 to around 145,400 pounds for the 737-8, varying by model and configuration to account for differences in size and intended use. These limits are established during to ensure structural integrity across operational scenarios.

Maximum Takeoff Weight

The maximum takeoff weight (MTOW) represents the highest total mass at which an is certified for safe takeoff, encompassing the operating empty weight (OEW), usable , , and any , as authorized by the aircraft's . This limit ensures the meets all structural, , and operational requirements under certified conditions, preventing risks such as excessive stress on the or insufficient climb . Manufacturers establish the MTOW during the design phase, balancing these elements to comply with regulatory standards while optimizing for intended missions. In relation to OEW, the MTOW forms the upper boundary of allowable mass, expressed conceptually as MTOW = OEW + usable + , where OEW serves as the baseline configured empty mass before operational additions. This hierarchy is certified by authorities like the FAA, which verify through type certification that the can operate safely at this weight without exceeding structural limits or compromising engine and lift capabilities. Unlike zero fuel weight, which excludes to protect structures from bending stresses, MTOW incorporates for complete operational loading. The determination of MTOW accounts for key design and environmental factors, including runway length, altitude, and temperature, which influence the aircraft's ability to accelerate and climb adequately during takeoff. For instance, higher altitudes and temperatures reduce air density, necessitating a lower MTOW to maintain performance margins, while longer runways allow for higher certified weights. Aircraft type also plays a role; narrow-body jets like the A320 have an MTOW of approximately 78,000 kg (172,000 lbs), tailored for medium-haul efficiency. These factors are rigorously evaluated during type to ensure the MTOW supports safe operations across diverse conditions, with any exceedance potentially leading to regulatory violations or structural failure.

Calculation and Verification

Weighing Procedures

The initial determination of the basic empty weight (BEW)—which forms the foundation for the operating empty weight (OEW)—involves a precise physical weighing of the aircraft during manufacturing or certification to establish the baseline weight and center of gravity (CG) position. This process ensures compliance with certification requirements by measuring the aircraft in its configured state, including all fixed equipment, unusable fuel, full operating fluids such as oil and hydraulic fluid, and any required ballast, while excluding usable fuel, payload, crew, and operational items. The aircraft is typically weighed at three or more support points—such as the nose gear and main landing gears—using calibrated scales to capture the total weight distribution accurately. OEW is then calculated by adding to the BEW the weights of the required flight (typically using standard averages of 190 pounds (86 kg) per member including , or operator-specific values from surveys per FAA guidance), personal equipment, , and standard operational items such as supplies, potable water, manuals, and emergency gear. Prior to weighing, the must be prepared in a controlled environment, such as a closed , to minimize external influences like wind or temperature variations. It is cleaned thoroughly, leveled both laterally and longitudinally according to the manufacturer's specifications (often using built-in leveling devices or jacks), and configured in an "as-delivered" state with all doors and access panels closed, systems powered off, and fluids at standard levels (e.g., full but drained usable ). This configuration aligns with the components of BEW, ensuring the measurement reflects the 's structural and fixed systems without extraneous variables. Certified weighing equipment, such as platform scales or electronic load cells, is required to achieve accuracy within 0.1% of the 's total weight. Platform scales are placed under each strut, while load cells may involve jacking the to a level flight attitude for precise readings. All scales must be calibrated annually or per the manufacturer's interval, zeroed before use, and any tare weights (e.g., from scale platforms) subtracted from gross readings to obtain net weights at each point. These standards are outlined in FAA guidance to guarantee reliable data for . Once weights are recorded, the BEW is calculated as the sum of the net weights from all scales, and the empty weight CG is determined using moment arm formulas relative to a manufacturer-specified datum (e.g., a point on the or ). The moment for each weighing point is computed as the product of its net weight and horizontal distance from the datum, with the total moment summed across points. The CG position is then: CG=∑(weight×arm)total weight\text{CG} = \frac{\sum (\text{weight} \times \text{arm})}{\text{total weight}} This yields the longitudinal CG in inches (or percentage of mean aerodynamic chord for larger aircraft), ensuring it falls within certified limits. Vertical and lateral CG may also be assessed if required, but the primary focus is longitudinal for balance computations. The CG for OEW is then adjusted based on the added operational items. The initial weighing occurs at the point of manufacture or prior to entry into service, with results documented in the official Weight and Balance Report, which includes scale certifications, configuration details, and calculations for ongoing reference. This establishes the foundational BEW data, which must be verified against Type Certificate Data Sheet limits before the aircraft is approved for operation.

Updates and Adjustments

Operating empty weight (OEW) requires ongoing updates following initial to reflect changes in the aircraft's configuration and ensure continued accuracy in weight and balance computations. Common reasons for these updates include aircraft modifications, such as the addition of , seats, or interior components, as well as equipment changes like the replacement of engines or units. Additionally, operators implement periodic re-weighing programs, typically every 36 to 48 months, to verify the baseline established during initial weighing and account for gradual wear or minor undocumented shifts. Adjustments to the BEW (and thus OEW) are calculated by adding or subtracting the weights of modified or changed items from the previous BEW value, often using manufacturer-provided data for the precise weights and locations of components. The center of gravity (CG) is then re-determined to maintain balance limits. For instance, installing new might increase BEW by the item's weight while shifting the CG forward if mounted near the . If cumulative changes exceed 0.5% of the or affect the CG range, a full re-weighing is recommended to confirm calculations. The updated OEW and CG are derived accordingly by incorporating the operational items. Documentation of these updates is essential and involves revising the (AFM) and all weight and balance records to incorporate the new BEW, OEW, and CG . The adjustment can be expressed mathematically as follows: New BEW = old BEW + Δweight CG shift = (Δweight × Δarm) / new BEW where Δweight is the net change in weight and Δarm is the distance from the datum to the item's location. OEW is then recalculated using the updated BEW. Operators, particularly airlines, bear the responsibility of tracking all cumulative modifications through detailed logs to prevent exceeding weight limits or compromising operational envelopes. This includes maintaining records of even small changes—such as those over 1 pound for —and ensuring that adjustments are certified by FAA-approved mechanics before flight resumption.

Applications and Significance

Role in Weight and Balance

In the weight and balance process for aircraft, pilots and operators begin pre-flight computations with the operating empty weight (OEW) as the foundational baseline, to which the weights of fuel, passengers, and cargo are sequentially added to determine the total aircraft weight and ensure it does not exceed maximum limits. This step involves plotting the cumulative loads on aircraft-specific loading diagrams or envelopes, verifying that the resulting center of gravity (CG) position remains within certified forward and aft boundaries to maintain stability and control throughout all flight phases. Accurate OEW data is essential here, as it incorporates the aircraft's configured empty state, including crew and standard operational items, providing a reliable starting point without the variability of payload elements. The core computation steps for total weight and CG utilize straightforward additive methods: the total weight is calculated as OEW plus the weight of usable fuel plus (passengers and ). For CG determination, the index or moment method is applied, where the total moment is the sum of the OEW moment, fuel moment, and moment; the CG position is then derived by dividing the total moment by the total weight, often expressed as a of the aerodynamic chord (MAC) for precision in larger aircraft. These calculations ensure the CG stays aft of the forward limit to prevent excessive stability and forward of the aft limit to avoid reduced control authority. Pilots perform these computations using tools such as manual weight and balance logs, loading schedules with moment index tables, or advanced electronic flight bags (EFBs) that automate inputs and generate real-time envelope visualizations. For instance, in a regional like the , the OEW CG is calculated and must remain within the aircraft's certified limits, from 4% to 40% MAC, to accommodate added loads without shifting outside safe margins. EFB software integrates OEW data with live gauges and passenger manifests, streamlining verification and reducing manual errors compared to traditional methods. Maintaining precise OEW records is crucial for error prevention, as inaccuracies can lead to CG excursions beyond certified envelopes, potentially causing stalls, structural overload, or loss of directional control during takeoff or landing. By anchoring computations to verified OEW, operators comply with safety protocols, mitigating risks from load shifts or configuration changes that could otherwise compromise flight safety.

Impact on Performance and Safety

A higher operating empty weight (OEW) directly limits an aircraft's payload and fuel capacity within the maximum takeoff weight constraints, thereby reducing overall range and necessitating longer runways for takeoff and landing. According to the Breguet range equation, which models jet aircraft range as proportional to the natural logarithm of the ratio between gross weight and empty weight, an increase in OEW diminishes this ratio and thus shortens maximum range for a given mission. For instance, in typical commercial configurations, a 10% rise in OEW can significantly curtail range while also impairing climb performance and maximum altitude capabilities. Incorrect OEW documentation or calculations can precipitate overweight conditions during flight, compromising structural integrity and altering the center of gravity (CG), which in turn affects stability and control. An aft-shifted CG from excess weight reduces and elevator effectiveness, increasing risk, while a forward CG elevates speed and landing distances. Historical incidents underscore these hazards; in the 2003 crash, understated empty weight and flawed balance computations resulted in an overweight 1900D with an aft CG beyond limits, leading to loss of pitch control, , and the deaths of all 21 aboard. Similarly, the 2008 Sikorsky S-61N accident involved an intentional understatement of empty weight by 1,437 pounds, causing overload, insufficient performance margin, and a fatal crash that killed nine during a high-elevation takeoff. Aircraft manufacturers optimize OEW to enhance , often employing advanced lightweight materials such as carbon-fiber composites, which can reduce structural weight by 15-30%. The exemplifies this approach, with composites comprising 50% of its structure by weight, enabling a 20% improvement in over predecessors partly through lower OEW relative to capacity. From an economic perspective, minimizing OEW expands the allowable for revenue-generating cargo or passengers, directly boosting profitability by increasing load factors without additional burn. This weight savings translates to lower operating costs per passenger mile, as reduced OEW permits more flexible mission profiles and higher utilization rates on routes.

Regulatory Framework

FAA Standards

The (FAA) defines operational empty weight (OEW) as the basic empty weight or fleet empty weight plus operational items, such as required , their baggage, and standard provisions like meals or potable water for transport category . This aligns with the standard empty weight—encompassing the , engines, fixed equipment, unusable fuel, and full operating fluids—augmented by for operational contexts in larger . Under 14 CFR Part 25, which governs transport category airplanes, the FAA mandates determination of OEW as part of type certification to establish airworthiness limits for weight and center of gravity (CG), as outlined in Advisory Circular 120-27F (2019). Weighing must achieve sufficient accuracy, with reestablishment of OEW required if cumulative changes exceed ±0.5% of the maximum landing weight or if CG shifts surpass ±0.5% of the mean aerodynamic chord (MAC). For operations under 14 CFR Parts 121 and 135, 120-27F outlines requirements for operators to develop approved weight and balance control programs, including maintenance of current OEW records for each or fleet. Periodic verifications are mandatory, such as individual weighings every 36 months or fleet sampling based on size (e.g., at least 10% of over nine in a fleet). Non-compliance with these OEW standards, such as inaccurate reporting during FAA audits, can result in violations of airworthiness requirements under 14 CFR § 121.153 or § 135.63, potentially leading to enforcement actions including civil penalties or operational restrictions.

International Standards

In the European regulatory framework, the (EASA) employs the term "dry operating weight" (DOW) under Certification Specifications for Large Aeroplanes (CS-25, Amendment 27, 2024) as the equivalent to operating empty weight, encompassing the basic empty weight plus , standard operational items, and full potable for the intended flight duration, while excluding usable , passengers, , , and supplies. This definition aligns closely with the U.S. operating empty weight but imposes stricter requirements for including potable and lavatory servicing fluids as part of operational readiness, ensuring consistency in weight and balance calculations for European-registered aircraft. The International Civil Aviation Organization (ICAO) provides guidelines in Annex 6, Part I, recommending standardized concepts for empty and operating weights to facilitate harmonization across international commercial air transport operations. These standards emphasize uniform application for flight planning and performance. Other national authorities, such as Transport Canada, define "aeroplane operational empty weight" in Standards 724 and 725 as the aircraft's actual weight prior to loading passengers, baggage, or cargo, incorporating crew, catering, pantry supplies, unusable fuel, and operational liquids. Similarly, Australia's Civil Aviation Safety Authority (CASA) aligns its empty weight definition with international norms, including all fixed equipment, mandatory operational items, unusable fuel, and full engine oil. Efforts to harmonize these variations are advanced through bilateral agreements, such as the FAA-EASA Bilateral Aviation Safety Agreement (BASA) and its Technical Implementation Procedures, which enable reciprocal validation of airworthiness certifications, including weight and balance data in export reports, to reduce discrepancies and streamline global aircraft operations.

References

  1. https://www.faa.gov/sites/faa.gov/files/2023-09/Weight_Balance_Handbook.pdf
  2. https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_120-27F.pdf
  3. https://www.federalregister.gov/documents/2004/08/19/04-18905/announcement-of-faa-advisory-circular-ac-120-27d-aircraft-weight-and-balance-control
  4. https://www.faa.gov/sites/faa.gov/files/12_phak_ch10.pdf
  5. https://www.faa.gov/regulations_policies/policy_guidance/benefit_cost/econ-value-section-6-perf-factors.pdf
  6. https://ansperformance.eu/acronym/oew/
  7. https://skybrary.aero/sites/default/files/bookshelf/2263.pdf
  8. https://cessna.txtav.com/en/piston/cessna-skyhawk
  9. https://www.law.cornell.edu/cfr/text/14/125.9
  10. https://www.boeing.com/content/dam/boeing/boeingdotcom/commercial/airports/acaps/737MAX_RevD.pdf
  11. https://www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/airplane_handbook/14_afh_ch13.pdf
  12. https://www.boeing.com/content/dam/boeing/boeingdotcom/company/about_bca/startup/pdf/historical/737NG_passenger.pdf
  13. https://www.ecfr.gov/current/title-14/chapter-II/subchapter-A/part-298/subpart-A/section-298.2
  14. https://skybrary.aero/articles/maximum-takeoff-mass-mtom
  15. https://pilotinstitute.com/airplane-weight-and-balance/
  16. https://www.ecfr.gov/current/title-14/chapter-I/subchapter-C/part-23
  17. https://simpleflying.com/factors-impacting-takeoff-performance-list/
  18. https://aircraft.airbus.com/en/aircraft/a320-family/a320ceo
  19. https://www.duncanaviation.aero/files/straight-talk/straight_talk-certifications.pdf
  20. http://d16bsf97ryvc45.cloudfront.net/Media/2012/10/1900d.pdf
  21. https://www.universalweather.com/blog/aircraft-weight-equipment-impact-on-flight-planning-part-1-basic-considerations/
  22. https://www.supercoolprops.com/home/articles/breguet.html
  23. https://www.cfinotebook.net/notebook/aerodynamics-and-performance/weight-and-balance.php
  24. https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR0401.pdf
  25. https://flightsafety.org/asw-article/weighty-issues/
  26. https://www.academicpublishers.org/journals/index.php/ijme/article/download/1850/2862/5629
  27. https://www.boeing.com/content/dam/boeing/boeingdotcom/features/innovation-quarterly/2024/IQ-2024-Q3-full.pdf
  28. https://www.seattletimes.com/business/heavier-787-will-still-meet-performance-targets-boeing-says/
  29. https://www.aircraftmonitor.com/uploads/1/5/9/9/15993320/aircraft_payload_range_analysis_for_financiers___v2.pdf
  30. https://www.easa.europa.eu/sites/default/files/dfu/CS-25_Amdt%203_19.09.07_Consolidated%20version.pdf
  31. https://safetyfirst.airbus.com/understanding-weight-and-balance/
  32. https://www.icao.int/publications/Documents/Annex_6_Part_I.pdf
  33. https://tc.canada.ca/en/corporate-services/acts-regulations/list-regulations/canadian-aviation-regulations-sor-96-433/standards/standard-724-commuter-operations-aeroplanes-canadian-aviation-regulations-cars
  34. https://www.casa.gov.au/sites/default/files/2021-09/weight_control.pdf
  35. https://www.faa.gov/sites/faa.gov/files/EUTIP_Rev6_w_amdt1_amdt2.pdf
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