Source: https://www.scribd.com/document/215256576/AC-20-161
Timestamp: 2019-01-16 06:54:41
Document Index: 362361426

Matched Legal Cases: ['arts 23', 'arts 91', '§ 23', '§ 23', '§ 23', '§ 23', '§ 21', '§ 23', '§ 23', '§ 23', '§ 23', '§ 25', '§ 23', '§ 23', '§ 23', '§ 23', '§ 23', '§ 23', '§ 23', '§ 23', '§ 23', '§ 23', '§ 23', '§ 23', '§ 23', 'art 23', 'art 23', 'art 23', 'arts 27', 'art 23', '§ 21', 'art 25', '§ 23', 'arts 91', 'arts 121', 'art 91', 'art 21', 'art 23', 'art 25', 'art 27', 'art 29', 'art 43', 'art 119', 'art 91', 'art 135', 'art 125', 'art 121', 'art 121', 'art 121', 'art 23', 'art 121', 'art 121', 'art 23']

AC_20-161 | Accuracy And Precision | Aeronautics
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CHAPTER 1. INTRODUCTION 1-1. PURPOSE.
a. This advisory circular (AC) will show you how to gain Federal Aviation Administration (FAA) approval of aircraft onboard weight and balance systems (OBWBS). We at the FAA recommend you use additional documents, referenced throughout this AC, to help you show compliance with the regulatory requirements of your type or supplemental type certification program. The documents supplement the engineering and operational judgment used to form the basis of any compliance findings on OBWBS. b. This AC is not mandatory and does not constitute a regulation. It describes an acceptable means, but is not the only means, to show you how to gain certification for OBWBS. However, if you use the means described in this AC, you must follow it entirely. Because the method of compliance presented is not mandatory, the term “must” applies only to an applicant who chooses to follow this particular method in its entirety. 1-2. WHO DOES THIS AC AFFECT. a. Chapter 2 provides guidance for type certificate holders who are installing an OBWBS under Title 14 of the Code of Federal Regulations (14 CFR) parts 23, 25, 27, or 29. b. Chapter 3 provides guidance for operational certificate holders who are required to have an approved weight and balance control program under 14 CFR parts 91 subpart K, 121, 125, or 135. 1-3. WHAT TYPES OF CERTIFICATION GUIDANCE IS COVERED IN THIS AC. This guidance is for applicants seeking certification through: • Type certification (TC), • Supplemental type certification (STC), • Amended type certificate (ATC), • Amended supplemental type certificate (ASTC), or • Parts Manufacturer Approval (PMA). 1-4. WHY USE AN OBWBS VS. STANDARD PRACTICE. a. For many years, international best practice has allowed the use of standardized passenger weights to calculate the aircraft’s take-off weight and center of gravity (CG) as part of an approved weight and balance control program. Using standardized weights assumed that the individual weights of passengers averaged out to a mean weight. When the aircraft’s passenger load is calculated this way it would not cause the aircraft weight limitation to be exceeded.
However, differences between the actual passenger load weight and the calculated passenger load weight can occur when using these standard passenger weights due to variation in actual passenger weights. To help eliminate these differences, an aircraft OBWBS can calculate the actual weight and CG of the aircraft (within accuracy tolerances of the OBWBS), and therefore remove the need to use standard passenger weights. b. Calculating an aircraft’s weight and CG accurately before flight is essential to comply with the certification limits established for the aircraft. These limits include various weight and CG limits, such as zero fuel, taxi, takeoff, flight, and landing limits. Aircraft manufacturers specify a maximum certificated take-off weight as well as CG limitations, and provide data on the performance capabilities of the aircraft. The most restrictive condition for a given take-off determines the allowable take-off weight and CG limitations. c. An OBWBS certified to weigh an aircraft and compute CG from equipment onboard the aircraft can be the primary means of providing weight and balance information if it receives certification and operational approval. d. The design of the OBWBS, and the OBWBS operating procedures and system limitations must all be consistent with how the OBWBS determines the weight and CG location used to dispatch the aircraft.
Type Certification. including the aircraft system interfaces and any aircraft system modifications made to accommodate the OBWBS installation. Systems. 25. (3) Certification basis and means of compliance. (6) Test plan. 27.771(a) 14 CFR §§ 23. The OBWBS must also be approved for operation by the FAA’s Flight Standards Operations inspectors. We recommend that you submit it early in the certification process. To install an OBWBS you must meet the certification guidelines in this AC. OBWBS ACCEPTABLE MEANS OF COMPLIANCE.1317 Page 4 . 25. (7) Conformity plan. 25. Parts Manufacturer Approval Procedure. (4) Communication and coordination. Prepare a certification plan that covers the installation of the OBWBS equipment. and (9) Compliance documentation. 29.50(b) 14 CFR §§ 23. Coordinate the certification program with the responsible FAA Aircraft Certification Office as described in FAA Order 8110. or in Order 8110-42. How to Establish the Certification Basis for Changed Aeronautical Products. Include the following items: (1) Project description and schedule. 29.1301 14 CFR §§ 23. b.48. a. (5) Human factors plan. Order 8110. 29. An acceptable means of compliance with the applicable airworthiness regulations must address the following regulations as a minimum: Instructions for Continued Airworthiness and Maintenance Manuals Equipment Function and Installation Equipment. Certification Plan. CERTIFICATION PROCESS FOR INSTALLING AN OBWBS 2-1. 25. through the certification program notification (CPN) process.1309 14 CFR §§ 23. (8) Continued airworthiness plan. 27. Means of Compliance. See chapter 3 of this AC for guidance on how to obtain approval as a primary dispatch system for operations.1308.4C.4/11/2008 AC 20-161 CHAPTER 2. 27. and Installations Pilot Compartment High-intensity Radiated Fields (HIRF) Protection 14 CFR § 21.1317. 29. 27. (2) System description.
operational accuracy. 29. 25. (3) Include limitations and systems operating instructions in the AFM/AFMS and the instructions for continued airworthiness.1357 14 CFR §§ 23. 29. 25. 25. and Advisory Lights Electrical Systems and Equipment – General Circuit Protective Devices Hydraulic Systems Pressurization and Pneumatic Systems Weight & Center of Gravity Instructions for Continued Airworthiness Aircraft Flight Manual – General Operating Limitations Lightning and Static Electricity Fire Protection Loading Information Electronic Equipment Electric Cables Switches Instrument Systems 14 CFR §§ 23.1359. 25. document RTCA DO 178B.1581 14 CFR §§ 23. 27. Caution. 27. 27.1435 14 CFR §§ 23. Software Conditions in Airborne systems and Equipment Certification. 27.1367 14 CFR §§ 25. or the most current revision. and 29.1589. 29. 25. and repeatability of the installed OBWBS.1438 14 CFR §§ 23.1322 14 CFR §§ 23. 27. Inc. 29.869. and Page 5 .777(a) 14 CFR §§ 23.4/11/2008 AC 20-161 Cockpit Controls Instrument Arrangement and Visibility Warning. dated December 1.1316 14 CFR §§ 23.867 and 25. 27. (4) If software is used. 25. 27.1519 14 CFR §§ 23. 27. 29.1333 (1) Demonstrate the system accuracy. 29.1333 and 29. and 29.1589 14 CFR §§ 23.1529 14 CFR §§ 23. 25.1365 and 27.1431 14 CFR §§ 23. 27.1321 14 CFR §§ 23. 25. 25.1583 14 CFR §§ 23. 27. (2) Demonstrate system accuracy for the maximum time period allowed between OBWBS calibration on the installed OBWBS. 27.1365 14 CFR §§ 23. 25. 29.1351 14 CFR §§ 23. 1992.1359 14 CFR §§ 23. 25. 29. 29.1367 and 27.1431 and 25. See paragraphs 2-2 and 2-3 in the AC for guidance. 25.1589. 29. 29. (a) You must meet the requirements in: • Radio Technical Commission for Aeronautics (RTCA). 27.
Work with your aircraft certification office (ACO) to determine which method to use to demonstrate the OBWBS system and operational accuracy requirements. or 29 aircraft should include demonstrations of the OBWBS system accuracy and the OBWBS operational accuracy. meet the requirements in: • RTCA DO-254. takeoff climb. Examples of performance-limited weights include weights limited by takeoff distance. This weight accuracy is used to determine CG accuracy to ensure that the calculated CG remains within the certificated CG limits. or the most current revision. dated November 1. RTCA/DO-254 Design Assurance Guidance for Airborne Electronic Hardware. Certification of Normal Category Rotorcraft. landing climb. (6) If the hardware contains complex electrical devices performing functions that cannot be evaluated by tests or analysis. a. Equipment Systems and Installations in Part 23 Airplanes. or the most current revision. Ground Tests. or the most current revision. • AC 27-1. Certification Considerations for Highly Integrated or Complex Aircraft Systems. and landing distance. As part of compliance with the airworthiness requirements. Weight and Balance Curtailment. and • AC 20-152.1309-1. When ground tests are required you can reduce the total number of aircraft ground tests by using a validated simulation of the aircraft and the OBWBS installation. 2007. and • AC 29-2. obstacle clearance. dated December 6. en route climb. Design Assurance Guidance for Airborne Electronic Hardware. System Design and Analysis. Certification of an OBWBS installation on a 14 CFR part 23. 1996. The fidelity and accuracy of the simulation model should be substantiated with actual aircraft Page 6 . 27. Environmental Conditions and Test Procedures for Airborne Equipment. • AC 25. accelerate-stop distance. b. CERTIFYING THE OBWBS ACCURACY UNDER ENVIRONMENTAL INFLUENCES. you must demonstrate the accuracy within the specified tolerances and the reliability of the installed OBWBS. Certification of Transport Category Rotorcraft. 2-2. approach climb. apply the curtailment to both structural and performance limited weights.4/11/2008 AC 20-161 • Society of Automotive Engineers (SAE) International Aerospace Recommended Practice (ARP) 4754. See paragraph 2-3 of this AC for a description of methods. (b) For additional guidance see FAA advisory circulars: • AC 23. 25. (7) You must also follow the environmental requirements in RTCA/DO-160F.1309-1. If a method in this AC determines that a weight curtailment is required.
e. Adapt these principles appropriately for other configurations. displayed values must be adjusted to account for operational accuracy before being compared to the applicable operational weight and balance limits. OBWBS Display of Weight and Balance Measurements. aircraft configuration changes (flaps. Simulation validation is necessary in order to establish that the simulation matches the actual aircraft behavior. (b) The (system or operational) CG position accuracies can be determined from the actual main gear and nose gear load accuracies for the OBWBS installation. You choose which of these Page 7 . This accuracy is the OBWBS system accuracy. The CG position calculated using the measured weight on the main landing gear and nose gear is the measured CG position. The accuracy of the OBWBS weight and balance measurements may decrease when the aircraft is disturbed by temperature changes. This accuracy is the OBWBS operational accuracy. (2) OBWBS Operational Accuracy. On the other hand. Terms. Basic Principles of OBWBS Accuracy Demonstration Methods. An OBWBS achieves its most accurate weight and balance measurements on a motionless aircraft in a controlled (temperature regulated. fixed aircraft configuration. (2) Calculating Under Operational and Environmental Conditions. The OBWBS separately measures the load on the nose gear and the load on the main gear. the displayed OBWBS output can be compared directly to the applicable operational weight and balance limits. winds. The results from further simulated ground tests carried out with the validated simulator may then be used in lieu of further physical ground tests. The OBWBS is expected to operate routinely in this disturbed environment. c. or you can demonstrate through analysis or test. (a) The CG position (system or operational) accuracy derives from weight accuracy through the geometry of the airplane landing gear and the load measured on each landing gear.4/11/2008 AC 20-161 ground tests. is the total airplane weight. (1) Determining CG. slat motion) or payload shifting (passenger movement). the displayed measurements do not take the operational accuracy into account. d. The following basic principles apply to three gear tricycle configurations. (1) OBWBS System Accuracy. The cumulative operational accuracy of two or more operational or environmental conditions can be calculated by taking the square root of the sum of the squares of the accuracies (addition in quadrature). no payload movement) environment. If so. the OBWBS system may display weight and balance measurements that are affected by disturbances. For this type of OBWBS. that is. and the weight of the landing gear itself. The sum of the measured loads on all landing gear. An OBWBS can display weight and balance measurements that take into account the established operational accuracy of the system and any necessary curtailments. no winds.
are accepted without weight curtailments for OBWBS operational accuracy. for the full range of takeoff weights. Consider airframe manufacturer-provided guidance regarding application of additional curtailments in adverse environmental conditions (such as wind gusts greater than 35 knots) or unique environments (such as airports with elevations above 6. AC 120-27E. or a 100 foot increase in takeoff or accelerate-stop distance. whichever is greater.5 knot change in V1 or V2 speed. provides instructions on how to accomplish precision airplane weight measurements. 2-3. This operational weight accuracy is used to determine CG accuracy. Takeoff Performance Based Method. numerical tables or step-by-step instructions in the AFM/AFMS to determine the operational accuracy due to two or more operational or environmental conditions for a specific departure. The OBWBS may calculate and display that operational accuracy using operational or environmental condition data provided to the OBWBS. or you can refer to the AFM/AFMS for limitations. Aircraft Weight and Balance Control. Determine any additional curtailments by analysis and verify by testing that duplicates or simulates the operational conditions. OBWBS operational accuracies that result in at most a ± 1. whichever is greater. a. Provide charts. or a 100 foot increase in the takeoff or accelerate-stop distances. The AFM/AFMS limitations can state that in operational use. (4) Additional Curtailments. you must first obtain weight and CG measurements from the OBWBS with the aircraft in a controlled environment. (3) These errors may be used to determine a corresponding operational weight accuracy for a given takeoff weight. determine the size of the weight error that results in at most a ± 1.5 knot change in V1 or V2 speed. assume the OBWBS operational accuracy results in at most a ± 1. OBWBS operational accuracies that result in greater errors than these require appropriate curtailment. graphical look-up tables. or a 100 foot increase in the takeoff or accelerate-stop distances. OBWBS ACCURACY DETERMINATION METHODS. such additional curtailments need only be applied when applicable conditions exist. (1) This method examines the influence of OBWBS system and operational weight and balance accuracies on aircraft takeoff performance. For all the following accuracy determination methods (see paragraph 2-3 of this AC).000 feet) that exceed the parameters assumed in the AFM/AFMS specific limitations and conditions (see paragraph 2-9 of this AC).5 knot error change in either V1 or V2 speed.4/11/2008 AC 20-161 methods to employ. (2) From the minimum value of V1 to the maximum value of V2 speed. For example. (4) The operational accuracies derived from the impact on takeoff performance help determine the range of the allowable operational and environmental conditions for the OBWBS without curtailment for OBWBS operational accuracies. (3) Controlled Environment Measurements. whichever is greater. To establish the OBWBS system accuracy in a controlled environment the aircraft should be in a hangar sitting on precision aircraft scales. over a specific range of Page 8 .
4/11/2008 AC 20-161 wind gust or wind velocities for a given temperature day and given takeoff weight.a(1) of this AC are met and the OBWBS measured CG position ± the CG position operational accuracy remains within the takeoff limits of the CG envelope. or weight and balance manual.e.. This method uses OBWBS weight and balance measurements taken while the aircraft is subjected to a pre-defined range of environmental disturbances in order to establish operational accuracy and procedural adjustments (i. expressed as maximum weight. as published in the type certificate data sheet. Operational accuracy levels. • The OBWBS measured weight ± weight operational accuracy results in no more than a ± 1. and CG errors experienced are then applied as curtailments to the original manufacturer's envelope. b. The AFM/AFMS limitations section for a given temperature day may then list this wind gust range as a limitation on the use of the OBWBS results without curtailment for operational accuracy. but will typically result in the largest curtailments when compared to the other methods offered. (7) The operator should use an actual takeoff weight corresponding to the measured weight plus weight operational accuracy. or a 100 foot increase in the takeoff or acceleratestop distances. (5) The AFM/AFMS calls out operational accuracies as a function of the range of the operational and environmental conditions (see paragraph 2-9 of this AC). the OBWBS results must be curtailed for operational accuracy before using them for takeoff. The OBWBS weight and balance results may be used for takeoff without curtailment for operational accuracy only when the takeoff speed accuracy constraints specified in paragraph 2-3. AFM/AFMS. and the most adverse CG position corresponding to the measured CG position plus or minus the operational CG accuracy.a(5) of this AC. The operator may need to remove or shift payload to keep these values within the weight and balance envelope. This method offers the smallest hurdle to determination of an envelope for OBWBS operation. Specific Operations Method. and • The OBWBS measured CG position ± CG position operational accuracy remains within the takeoff limits of the CG envelope. These conditions determine the content of the limitations and conditions as described in paragraph 2-9 of this AC.5 knot change in V1 or V2 speed. (1) To demonstrate the OBWBS operational accuracy. Page 9 . weight and/or CG envelope curtailments). you should: • Establish the proposed range of operational and environmental conditions in which the OBWBS will operate. (6) If the cumulative OBWBS operational accuracy does not meet the criteria of paragraph 2-3. whichever is greater. See appendix 4 of this AC for an example of this method applied to a B767-300ER.
a of this AC. or procedures. See figure 1 in this AC. • For example. FIGURE 1. (1) Assess the load buildup method’s operational accuracy by considering a variety of factors recommended by the aircraft manufacturer and AC 120-27E. that ensure the airplane always operates within the certified weight and CG envelope. as guidance material. Curtail the limits of the CG envelope for any OBWBS operational accuracy that is worse than the accuracy of the load buildup method. The OBWBS operational accuracy may be compared to existing OEM and FAA recommended procedures for computing weight and balance values for a given aircraft configuration. (2) Use the OBWBS operational accuracy to identify all operational limitations (such as weight and/or CG envelope curtailments when operating at specific points in the range of limitation values) determined through this process in the AFM/AFMS. c. FACTORS TO CONSIDER FOR LOAD BUILDUP METHOD.4/11/2008 AC 20-161 • Ground test the OBWBS under each of the conditions identified in the limitations and conditions as described in paragraph 2-9. Factor Scale accuracy during reweigh Fuel quantity indicating accuracy Allowable weight/CG variation prior to “reestablishment” of operational empty weight (or allowance for potential variation due to use of fleet weights) Variation in catering/provisioning Variation in male/female ratio Page 10 Effect on Weight X X X Effect on CG X X X X X X X . The curtailed envelope applicable when using the load buildup method also applies to the OBWBS weight and CG measurements as long as OBWBS operational accuracy remains equal to or better than the accuracy determined for the load buildup method. The load buildup method weight and CG accuracies as derived from analysis of these procedures help determine the range of the allowable operational and environmental conditions for the OBWBS without curtailment for OBWBS operational accuracies. These procedures. have acceptable accuracies as proven in past service experience. Weight and Balance Procedures Method (Load Buildup Method). also known as load buildup methods. suppose the aircraft manufacturer provides environmental or operational limitations. Your OBWBS installation may operate within those same restrictions without demonstration. Aircraft Weight and Balance Control. You can use analysis as an alternative to testing if you can substantiate the analysis approach.
Capacitor-Type Gage System. dated July 2001. (b) Fuel quantity indicating accuracy – Typically 3% of full capacity. or the most current revision. (g) Crew weight variation – Typically a 25% variation in the standard crewmember weights. defined as tolerable error by AC 120-27E. See: • SAE AS-405C. or the most current revision. undetected. in galley provisioning. • Military document MIL-G-8798. typically 10% deviation from ratio upon which passenger weights were based. (d) Variation in catering/provisioning – Amount of variation that could be expected to exist. as outlined in AC 120-27E. or that amount found to be justified based upon sampling or survey of crewmember weights.2% of basic empty weight (BEW). as outlined in AC 120-27E. Fuel and Oil Quantity Instruments.4/11/2008 AC 20-161 Passenger weight variation Crew weight variation Baggage weight variation Cargo weight variation X X X X X X X X (2) Tolerable errors associated with each factor are as follows: (a) Scale accuracy for reweigh – Typically 0. or the most current revision. (c) Operational Empty Weight Variation – ½ of one percent of the mean aerodynamic chord (MAC) and ½ of one percent of maximum landing weight. or • MIL-G-26988C. 1992. Analog accuracy value may be used for aircraft for which the aircraft OEM guidance does not recommend or require the use of digital scales. (f) Passenger weight variation – Typically a 1% variation in passenger weight plus a 2% variation in carry-on baggage and personal item weights.1% of BEW for digital scale systems. Typically 20% of the standard galley stock or galley cart weights. General Specification for Liquid Quantity Gage. Page 11 . dated Sep 28. (e) Variation in male/female ratio – Amount of variation in ratio of male to female passengers permitted without adjusting passenger weights in use. General Specifications for FuelQuantity. 1995. based upon reported scale accuracy for analog scale systems or 0. dated September 30.
(4) In determining the OBWBS operational accuracy. (2) During a trial period in revenue service.a of this AC. (4) In demonstrating the OBWBS operational accuracy. the current load buildup system is used as the primary means of performing the weight and balance functions for the airplane. takeoff weight). These differences include load buildup curtailments as described in AC 120-27E. The cumulative accuracy of the load buildup method may be calculated by taking the square root of the sum of the squares of the factor accuracies (addition in quadrature). • Ground test the OBWBS under each of the conditions identified in the limitations and conditions as described in paragraph 2-9. such as baggage miscount.a of this AC. d. OBWBS Operational Demonstration Method. Page 12 . or in non-revenue operation as part of a planned ground test program. You choose which of these methods to employ. as defined as tolerable error by AC 120-27E. • Use the OBWBS operational accuracy to identify any operational limitations (such as weight and/or CG envelope curtailments when operating at specific points in the range of limitation values) determined through this process in the AFM or AFMS.4/11/2008 AC 20-161 (h) Baggage weight variation – Typically a 2% variation in baggage weight (including both checked and designed heavy weight bags). based upon typical scale accuracy. during the demonstrations with the OBWBS installed for evaluation purposes only. as applicable. or better than. (1) Continue to use the original weight and balance program. (3) Ground tests can demonstrate equivalent safety between an OBWBS implementation and the current load buildup system by comparing to precision aircraft scale weighing. These conditions determine the content of the limitations and conditions as described in paragraph 2-9. you should: • Establish the proposed range of operational and environmental conditions in which the OBWBS will operate. use the OBWBS system accuracy that is at least as accurate as. Aircraft Weight and Balance Control. (i) Cargo weight variation – Typically a 1% variation in actual cargo weight verses reported cargo weight. omitted cargo weights or omitted jump seat occupants. as well as differences in the weights being compared (for example. the current load buildup system. (3) The items eligible for consideration do not include those which originate from human error factors. and records all OBWBS measurements. This method may be used to evaluate OBWBS operational accuracy during revenue service for a trial period. Note that differences between the scale and load buildup CG’s may exist that would not be considered as part of the load buildup CG error. incorrect passenger count. or demonstrate through analysis or test. taxi weight vs.
the actual airplane weight can be obtained with a precision scale weighing of the loaded airplane prior to departure. at least 10% of the tests should be at weights within 10% of the minimum airplane takeoff weight. Show that the system complies with safety objectives. Dispatching an aircraft with calculated aircraft weight or CG within its certificated weight or CG limits when the aircraft is actually outside its weight or CG limits is hazardous/severe-major or catastrophic level of hazard depending on the magnitude of the weight or CG error. and the tests should cover the aircraft weight and CG envelopes. a. b. test applicable environmental considerations throughout the operating envelope. major. or catastrophic level of hazard depending on the magnitude of the weight or CG error. Conduct a minimum of twenty five weighing trials. SAFETY ASSESSMENT PROCESS GUIDANCE. Hazard severity can be mitigated by manufacturers’ recommended risk reduction strategies to protect against severely overloading the aircraft. Failure conditions. is a minor. You can find references for additional guidance on conducting safety assessments and analyses in appendix 1 of this AC. Any failure condition of the OBWBS must not affect the functioning of other systems nor reduce the integrity of other systems if the OBWBS interfaces Page 13 . During a revenue service demonstration. c. or severely loading the aircraft out of balance. or severely loading the aircraft out of balance. or other independent reasonableness checks on the OBWBS measured weight and CG position. or other independent reasonableness checks on the OBWBS measured weight and CG position. (7) At least 30% of the tests should be at weights within 10% of maximum airplane takeoff weight.4/11/2008 AC 20-161 (5) The limits of the OBWBS weight and CG envelope must be curtailed for any OBWBS operational accuracy that exceeds the accuracy of the load buildup method. Include sufficient trials in the demonstration plan to show to a confidence interval of at least 95% that the statistics of the OBWBS weight and balance measurements are at least as accurate as the original program being used. Hazard severity can be mitigated by manufacturers’ recommended risk reduction strategies to protect against severely overloading the aircraft. Determine the maximum acceptable levels of “probability of failure” for the system as installed on the aircraft. such as recommended operating and training procedures for loading the aircraft. Dispatching an aircraft with calculated aircraft weight or CG within its certificated weight or CG limits when the calculated aircraft weight or CG is incorrect. You must identify the levels of hazard associated with installation and use of the system. hazardous/severe-major. System Safety Assessments and Analyses. (6) Design the demonstration plan to allow multiple tests at multiple airplane weight and CG configurations. This error can have an effect on aircraft configuration or operational performance factors such as trim setting. (8) Also. but within the certified limits. such as recommended operating and training procedures for loading the aircraft. d. 2-4.
h. to limit the effects of a failure. f. Designed failure effect limits.4/11/2008 AC 20-161 with other aircraft systems. (3) Environmental hazards identification and qualification testing. Redundancy or backup systems to enable continued function after any single or any number of failures. j. to ensure that major failure conditions are remote. b. 2-5. e. manufacture. Design the OBWBS on objectives and principles of the fail-safe concept. pneumatic). The capability to check a component’s condition. test. Error Tolerance that considers adverse effects of foreseeable errors during the aircraft’s design. Designed failure path to control and direct the effects of a failure in a way that limits its safety impact. Flight crew procedures specifying corrective action for use after failure detection. c. to sustain damage. Failure warning or indication. SYSTEM DESIGN CONSIDERATIONS. components. Margins or Factors of Safety to allow for any undefined or unforeseeable adverse conditions. The use of only one of these principles is seldom adequate. Proven reliability so multiple independent failures are unlikely to occur at one time. hazardous failure conditions are extremely remote. Isolation of systems. operation. Designed integrity and quality. l. that is. g. including life limits to ensure intended function and prevent failures. which considers the effects of failures and combinations of failures in defining a safe design. The fail-safe design concept uses the following design principles in order to ensure a safe design. Page 14 . and catastrophic failure conditions are extremely improbable: a. hydraulic. k. and maintenance. (2) Connections to other aircraft systems. d. Other design considerations include: (1) Use of other aircraft systems (electrical. A combination of two or more is usually needed to provide a fail-safe design. and elements so the failure of one does not cause the failure of another. i.
2-8. installer. (3) Evaluation of identified failure modes. Regardless of what format is used. If using an OBWBS in aircraft flight operations show that it has no adverse impact or interferes with other aircraft systems. Items to consider for ground test include: (1) Self test functions (built in test equipment). printer. or other compatible display systems. Conduct a certification flight test for the first OBWBS installation to verify the installation integrity and demonstrate that the installed OBWBS has no adverse impact on other aircraft systems. (4) Evaluation of location of OBWBS controls. Determine the accuracy of the OBWBS by test or by analyses that are verified by testing. The OBWBS must display the collected data (weight and CG) in a form easily understood by the flight crew. and aircraft system architecture. for equipment operating in an airborne environment. TEST CONSIDERATIONS. A manufacturer.b. The level of testing required will be determined by the scope of the installation. and the presentation of pertinent weight and CG data to the flight crew. Means of Compliance. Ground Test.4/11/2008 AC 20-161 2-6. in this AC. and AC 23. Transport Category Airplane Electronic Display Systems. or operator can test and validate to ensure proper operation and non-interference with other installed systems. If the OBWBS fails to function properly. and the features desired by the user. such as a multi-function display. a. use an alternative method of determining aircraft weight and CG location for dispatch. b. Find additional guidance on applicable display systems in: • • • Section 2-1. including radiated emissions. The indicated weight and CG position must as a minimum account for the system accuracy of the OBWBS. Show that the OBWBS meets appropriate industry-adopted environmental qualification standards. Base the level of flight test required to validate a particular OBWBS installation on the type of aircraft. Flight Test. 2-7. (2) Evaluation of all OBWBS aircraft interfaces. Conduct a certification ground test for each OBWBS installation. flight management system. simulation and ground testing. AC 25-11. BACKUP SYSTEM. DISPLAY SYSTEM. The display hardware can be stand-alone or interfaced with existing equipment. We will evaluate the actual requirement for Page 15 . We give credit for previously certified installations. Installation of Electronic Displays in Part 23 Airplanes. the options made available by OBWBS. This alternative method must be approved for operations requiring an operating certificate. the display presentation must show the crew data that’s organized and easily used. The actual display format used will depend on the onboard display hardware.1311-1B.
(c) Rain. Page 16 . dew. snow. 2-9. (e) Environmental temperature. (d) Ground slope. Total system accuracy. must determine the limitations of the OBWBS and how those limitations are accounted for by the OBWBS and the procedures described within the AFM/AFMS. You. and we will include operational and environmental considerations. Include any limitations affecting operations in the AFM/AFMS. or analysis verified by tests. Use this configuration for all operational aircraft weighing: (a) Wing flap and stabilizer positions. Conduct ground tests. Conduct ground tests. and dew on aircraft CG calculations must also be addressed. how they will affect aircraft operations. both lateral and longitudinal. to determine a reasonable weight and then subtract from the aircraft weight as displayed on the OBWBS with de-icing fluid. or analysis verified by tests. for an aircraft of known weight and CG to determine the effects of winds. All limitations and conditions must be identified to ensure the aircraft does not operate outside the certified CG envelope. must determine if there are any limitations of the system and. The effect of de-icing fluids on aircraft CG calculations must also be addressed. If ground tests or analysis provide data supporting a reduction in aircraft weight with these factors present. The OBWBS must have a means to account for ground slope. tailwinds. Limitations and Conditions. ice. and cross winds. State the established aircraft weighing configuration in the AFM/AFMS. You must test the effects of headwinds. and the effects upon accuracy due to environmental and operational limitations. The effect of rain. the applicant.4/11/2008 AC 20-161 a flight test for each installation. ice. then you can reduce aircraft weight by a standard weight used for the factor. (b) Oleo strut extension. (2) Configuration of aircraft to conduct a weighing. (b) De-icing fluids. As a minimum. snow. Demonstrate the effects on accuracy through tests or analysis over the temperature and pressure range that will be used. De-icing fluids depart the aircraft during roll-out. or provide guidance to compensate for the effects of ground slope. AIRCRAFT FLIGHT MANUAL/AIRCRAFT FLIGHT MANUAL SUPPLEMENT. system accuracy. as compared to the OBWBS displayed weight. frost. Establish aircraft weighing configuration during the ground test program. Include all limitations affecting flight operations in the following items. frost. if so. barometric pressure. as applicable: (1) Environmental: (a) Wind velocity and direction. provide instructions in the limitations section of the AFM/AFMS that include the following: a.
2-10. Recommended method of zero fuel weight and CG computation. 29. Format the ICA so it is compatible with other maintenance instructions for the aircraft. (d) Fuel load and its location.54. As applicable.50(b). Appendix A of 14 CFR parts 27. (f) Passenger.4/11/2008 AC 20-161 (c) Engine and auxiliary power unit thrust. 29. and Content. stabilizer. Instructions for Continued Airworthiness. 27. c. serving carts. Operational considerations for normal/abnormal procedures. a. maintenance instructions of the OBWBS and include calibration instructions and intervals. c. b. (g) Wing flap. You must specify periodic checks in the ICA to ensure the OBWBS reliability and accuracy remain acceptable. including any changes to that weight. and cargo door(s) positioning. and crew positioning. Appendix G of 14 CFR part 23. The ICA is required for the OBWBS. 25.1529. complete the ICA in accordance with: • • • • • 14 CFR § 21. jetway. Responsibilities. Appendix H of 14 CFR part 25. (e) Entrance and cargo door position. entrance door(s). (h) Stairways. Restricted times of operation. • FAA Order 8110. Address the integrity of system. b. INSTRUCTIONS FOR CONTINUED AIRWORTHINESS (ICA). or ground service connections. Page 17 . Address all applicable OBWBS installed under a particular modification within the ICA. As applicable. Restricted areas of operation. and any required information relating to the interface of the system with the aircraft. Requirements. e. Calibration must consider the effect of unsprung hardware weight. During the certification process of the aircraft onboard weight and balance system installation. 14 CFR §§ 23. d.
Each ICA must contain an “Airworthiness Limitations” section. If you have modified the OBWBS. MASTER MINIMUM EQUIPMENT LIST (MMEL). Page 18 . MMEL allowances must be substantiated based on the OBWBS functional hazard assessment.4/11/2008 AC 20-161 d. justification. 2-11. Submit the proposed MMEL. The MMEL must include an alternate method based on an acceptable conventional weight buildup to determine aircraft weight and CG location to be used if the OBWBS fails to function properly. Develop procedures for safely dispatching the aircraft using the MMEL. and procedures to the flight operations evaluation board chairman in the aircraft evaluation group for FAA evaluation and approval. Determine any MMEL allowance considering criticality of the OBWBS functionality. The FAA approving office (for example. Submit the MMEL with the OBWBS equipment changes to the FAA for approval. Develop a proposed MMEL with appropriate justification. flight standards district office) will coordinate with ACO engineering when evaluating the revised MMEL. revise the MMEL to address the OBWBS hardware or software changes.
and E096. Page 19 . or 135. and 214. 213. See AC 120-27E. This chapter is for certificate holders required to have an approved weight and balance control program under 14 CFR parts 91 Subpart K. OpsSpecs paragraphs E096 and A096 will be issued to certificate holders and program managers who are authorized to use only actual weights and an OBWBS. as applicable. and a conventional load build-up system. 125. 212. 3-2. Aircraft Weight and Balance Control. OPERATIONAL APPROVAL PROCESS FOR ONBOARD WEIGHT AND BALANCE SYSTEMS 3-1. a letter of authorization (LOA) number A096 or A097-A099 and A011 as applicable. A011. can be issued. If you develop and receive approval for a backup system. BACKUP SYSTEM. 3-3. and 14 CFR parts 121. the FAA may grant you relief to include an OBWBS in the operator’s minimum equipment list (MEL). as a back-up weight and balance system. If you are an operator. If you obtain operational approval for use of an OBWBS. OPERATIONS SPECIFICATIONS. chapter 2. Compliance with these guidelines allows you to use a certified OBWBS for primary dispatch. operations specifications (OpSpecs) will be issued by the FAA. use the guidance in the AC 120-27E to develop a backup system based on a conventional weight buildup. Operators authorized to use average weights as a back-up system will not be issued A096. will be issued OpSpec paragraphs A097-A099. OPERATIONAL APPROVAL GUIDANCE.4/11/2008 AC 20-161 CHAPTER 3. For 14 CFR part 91 operators. paragraphs 211. Operators that wish to use average weights.
RELATED REGULATIONS AND DOCUMENTS Regulations 14 CFR Part 21 14 CFR Part 23 14 CFR Part 25 14 CFR Part 27 14 CFR Part 29 14 CFR Part 43 14 CFR Part 119. Transition.693 14 CFR Part 91 14 CFR Part 135 14 CFR Part 125 Title Certification Procedures for Products and Parts Airworthiness Standards: Normal. Utility. and Commuter Category Airplanes Airworthiness Standards: Transport Category Airplanes Airworthiness Standards: Normal Category Rotorcraft Airworthiness Standards: Transport Category Rotorcraft Maintenance. Preventive Maintenance.49 14 CFR Part 121. and Alteration Contents of Operations Specifications Aircraft Requirements: General Continuing Analysis and Surveillance Pilots and Flight Engineers: Initial.422 14 CFR Part 121.4/11/2008 AC 20-161 Appendix 1 APPENDIX 1. Systems.373 14 CFR Part 121.1309-1C . and Installations in Part 23 Airplanes Page A1-1 Advisory Circulars AC 23.419 14 CFR Part 121. Rebuilding.153 14 CFR Part 121. and Upgrade Ground Training Aircraft Dispatchers: Initial and Transition Ground Training Load Manifest: All Certificate Holders General Operating and Flight Rules Operating Requirements: Commuter and On-Demand Operations Certification and Operations: Airplanes Having a Seating Capacity of 20 or More Passengers or a Maximum Payload Capacity of 6000 Pounds or More Title Equipment. Acrobatic.
1309-1A AC 25-11 AC 25. Change 1 AC 29-2C. and Content Industry Documents SAE ARP 4754 SAE ARP 4761 Title Certification Considerations for Highly-Integrated or Complex Aircraft Systems Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment Software Considerations in Airborne Systems and Equipment Certification Environmental Conditions and Test Procedures for Airborne Equipment Design Assurance Guidance for Airborne Electronic Hardware Page A1-2 RTCA DO-178B RTCA DO-160F RTCA DO-254 .4C Order 8110.4/11/2008 AC 20-161 Appendix 1 AC 23.54 Installation of Electronic Displays in Part 23 Airplanes System Design and Analysis Transport Category Airplane Electronic Display Systems Certification Maintenance Requirements Certification of Normal Category Rotorcraft Certification of Transport Category Rotorcraft Air Carrier Maintenance Programs Aircraft Weight and Balance Control Title Type Certification How to Establish the Certification Basis for Changed Aeronautical Products Parts Manufacturer Approval Procedure Instructions for Continued Airworthiness. Responsibilities.19 AC 27-1B.48 Order 8110-42 Order 8110. Change 1 AC 120-16 AC 120-27E FAA Orders Order 8110.1311-1B AC 25. Requirements.
includes. Failure Load Buildup System Maximum Zero Fuel Weight Onboard Weight and Balance System Primary Dispatch System Redundancy System Page A2-1 . parts. male to female passenger ratio. Note: Errors may cause failures. An occurrence that affects the operation of a component. part. and computes the aircraft center of gravity from equipment onboard the aircraft. A system that generates aircraft weight and balance data used to dispatch an aircraft for flight. The presence of more than one independent means for accomplishing a given function or flight operation. Method of establishing an aircraft’s weight and center of gravity with the assumptions established in AC 120-27E. fuel weight. average passenger weight.4/11/2008 AC 20-161 Appendix 2 APPENDIX 2. A combination of components. and balance information for use in primary dispatch of the aircraft. average bag weight. Aircraft Weight and Balance Control. TERMS AND DEFINITIONS Backup System Backup means of computing aircraft weight and balance for dispatching the aircraft instead of the primary one. which are interconnected to perform one or more functions. Weighs the aircraft and payload. The maximum permissible weight of an aircraft with no disposable fuel and oil. or element so it can no longer function as intended (Includes both loss of function and malfunction). The system displays the actual weight. but are not considered to be failures. and elements.
use the following formulas to determine how aircraft performance is affected by different weights and CG. and the weight error We. for example.1) ½ = 0.b(5) of this AC. airplane configuration and runway conditions.e. Let the measured weight Wm. The ratio of the takeoff velocity V1 at weight W1 to takeoff velocity V2 at weight W2 is given by: (V2 / V1) = (W2 / W1) ½ So. Let the measured CG location be CGm be defined as the sum of the actual CG location CGa and the CG location error CGe. the actual velocity needed for takeoff in terms of the velocity assumed to be needed for takeoff will be: Vactual = Vassumed / (1 + α) ½ If the measured airplane weight is 10% higher than the actual weight. allowable inaccuracies in the OBWBS measurements as a function of flight phase and functional hazard severity.) the airplane takeoff velocity is proportional to the square root of the airplane weight. the sum of the actual weight Wa.95 × Vassumed Page A3-1 . in takeoff. with all other factors held constant (i. where the CG location error is due to inaccuracy inherent in the system and to operational disturbances: CGm = CGa + CGe = (1 + α) × CGa and let 0 ≤ α < 1. For example. The ratio of the actual weight/erroneous weight and the actual CG position/erroneous CG position will establish a non-dimensional percentage accuracy bound on the acceptable. where the weight error is due to inaccuracy inherent in the system and to operational disturbances. the ratio of the actual weight/measured weight verses the actual takeoff velocity to assumed takeoff velocity is given by: (Vactual /Vassumed) = (Wa / (1 + α) × Wa) ½ = (1 / (1 + α)) ½ or rearranging the equation.4/11/2008 AC 20-161 Appendix 3 APPENDIX 3. be expressed as a percentage of Wa as: Wm = Wa + We = (1 + α) × Wa and let 0 ≤ α < 1. then: Vactual = Vassumed / (1 + 0. EFFECTS OF WEIGHT AND CG ON AIRCRAFT PERFORMANCE As referenced in section 2-3.
The ratio of the takeoff distance S1 at weight W1 to takeoff distance S2 at weight W2 is given by: (S2 / S1) = (W2 / W1) 2 So. and at a higher velocity than expected based on what the OBWBS measured weight indicated. and at a slower velocity than expected based on what the OBWBS measured weight indicated. for example. the ratio of the actual weight/measured weight verses the actual takeoff distance to assumed takeoff distance is given by: (S actual /S assumed) = (W a / (1 + α) × W a) 2 = (1 / (1 + α)) 2 or rearranging the equation. airplane configuration and runway conditions) the airplane takeoff distance is proportional to the square of the airplane weight.1) 2 = 0. The percentage error in weight measurement (and thus accuracy) can be related to a takeoff performance impact and its hazards.e.83 × S assumed and the crew finds the airplane can takeoff a shorter distance down the runway than expected based on what the OBWBS measured weight indicated. for example. If the measured airplane weight is 10% lower than the actual weight. in percent of actual airplane weight. for example then: Vactual = Vassumed / (1 .0. With all other factors held constant (i. EFFECTS OF WEIGHT AND CG ON AIRCRAFT PERFORMANCE. can result in a takeoff distance that exceeds available runway Page A3-2 . the actual distance needed for takeoff in terms of the assumed distance needed for takeoff will be: S actual = S assumed / (1 + α) 2 If the measured airplane weight is 10% higher than the actual weight. If the measured airplane weight is 10% lower than the actual weight.4/11/2008 AC 20-161 Appendix 3 APPENDIX 3. In the same manner the effect of weight errors (and thus accuracies) on takeoff distance can be assessed. then: S actual = S assumed / (1 .1) 2 = 1.05 × Vassumed and the crew might find the airplane takes off longer distance down the runway than expected.1) ½ = 1.0. A large enough error or inaccuracy. then: S actual = S assumed / (1 + 0. continued the crew might find the airplane can takeoff at a shorter distance down the runway than expected.23 × S assumed And the crew find the airplane takes off at a longer distance down the runway than expected as based on what the OBWBS measured weight indicated.
continued length or doesn’t allow for enough stopping distance if the crew elects to abort the takeoff. The percentage error in weight measurement (and thus accuracy) can be related to a takeoff performance impact and its hazards. EFFECTS OF WEIGHT AND CG ON AIRCRAFT PERFORMANCE.4/11/2008 AC 20-161 Appendix 3 APPENDIX 3. Page A3-3 .
TAKEOFF PERFORMANCE BASED METHOD GUIDANCE. or a 100 foot increase in takeoff or accelerate-stop distance. THE EFFECT OF WEIGHT CHANGE ON V1 SPEED.5-knot error or change in V1 or V2. Therefore. The applicant uses this guidance to map out an analysis approach that determines the need to curtail for the accuracy of the OBWBS-reported weight and CG position when using the OBWBS in operational conditions. this guidance will help an OBWBS applicant determine the operational accuracy for an OBWBS installed on a B767-300ER fleet using the takeoff performance based method. the applicant determines that across takeoff flap settings of 5. a. The AFM may present the information used to determine airplane takeoff performance speeds and required takeoff runway length as graphs.7 for the B767-300ER per AFM operationally defined limits). a. Use this relationship to determine the magnitude of weight error that results in a ± 1. This range is dubbed the low-weight “band.000 pounds to 250. c.knot change in V1. Review information published in the B767-300ER Airplane Flight Manual (AFM). b. For many airplanes the ratio of V1 to VR varies from 1. and that this relationship holds across the airplane weight range. d. a change in VR will not result in a change in V1 of greater magnitude than the change in VR . By definition the V1 speed is at or below VR. are accepted without curtailments or procedural adjustments for OBWBS operational accuracy. c.000 pounds. An applicant may use a computer program or parametric equations that can be shown to accurately represent the approved AFM data set. In general.g. or more than a 100 foot increase in takeoff or accelerate-stop distance.” Page A4-1 . In this example. the applicant may evaluate the effect of weight changes on VR and then relate this change to V1 using the appropriate ratio for the AFM operationally defined limits for the airplane type. require appropriate curtailment for operational accuracy.5.. TAKEOFF PERFORMANCE BASED METHOD EXAMPLE 4-1. 0. As referenced in section 2-3.5 knot error or change in V1 or V2. 4-2. whichever is greater. 15 and 20 degrees.0 (per regulation) to some lower limit (e.4/11/2008 AC 20-161 Appendix 4 APPENDIX 4. b.000 pounds results in a 3. the effect of airplane weight on VR as a function of the airplane’s weight can be represented as follows: (1) In the weight range of 200.c.(7) of this AC. OBWBS operational accuracies that result in greater than a ± 1. Interpolation may be required for weights not exactly shown on these charts. The applicant uses the AFM data to first determine the effect of airplane weight variation on V1 to establish the relationship between incremental weight change and resulting incremental V1 speed change. OBWBS operational accuracies that result in at most a ± 1. whichever is greater. the applicant sees that a change in weight of 10.5 knot change in VR.
4/11/2008 AC 20-161 Appendix 4 APPENDIX 4. This weight offset corresponds to an OBWBS weight accuracy of 2% above 250. and that this relationship holds across the airplane weight range.5 knot change in VR.5 knot change) = ± 6. the applicant sees that a change in weight of 10. • ± 1.5 knot change × (10.000 pounds/ 3 knot change) = ± 5. continued (2) In the weight range of 250. (1) In the weight range of 200. and that this relationship holds across the airplane weight range. THE EFFECT OF WEIGHT CHANGE ON V2 SPEED. and that this relationship holds across the low-weight band.286 pounds in the lowweight band. The analysis of the effect of airplane weight change on V2 is similar to the analysis of the effect of airplane weight change on V1.000 pounds to 1.0. the applicant sees that a change in weight of 10. TAKEOFF PERFORMANCE BASED METHOD EXAMPLE.000 pounds. a. the applicant determines from the AFM data that across takeoff flap settings of 5.000 pounds over the lowweight band.75 knot change in V2. The relationships in these bands can scale by the ratio of V1/VR for those performance scenarios using a V1/VR ratio less than 1. The OBWBS accuracies resulting in at most a ± 1.000 pounds results in a 3 knot change in VR. There is no need to relate the analysis to VR data. Page A4-2 .” d.72% accuracy at 250.000 pounds. the applicant sees that a change in weight of 10.000 pounds in the high.000 pounds over the mid-weight band. 4-3.000 pounds results in a 2.000 pounds in the midweight band. This weight offset corresponds to an OBWBS weight accuracy of 1.43 % accuracy at 350. except that V2 AFM data are readily available. This range is dubbed the mid-weight “band.000 pounds to 1. Alternatively. This range is dubbed the high-weight “band.weight band.000 pounds to 350.” (3) In the weight range of 350. e.000 pounds/ 3.0 are therefore: • ± 1.5 knot change × (10. With respect to V2.4 % accuracy at 430.5-knot change in V1 in each band when using a V1/VR ratio of 1.000 pounds results in a 2.000 pounds over the high-weight band. the applicant can fit a curve across these bands in order to smooth out the discontinuities or jumps in weights at the band edges. • ± 1. 15 and 20 degrees of flap.000 pounds.5 knot change × (10.000 pounds/ 2.71% above 350. This weight offset corresponds to an OBWBS weight accuracy of 2. f.000 pounds to 1. or ± 4300 pounds with rounding.15% at 200.5 knot change) = ± 4.000 pounds to 250. b.000 to 430.
This weight offset corresponds to an OBWBS weight accuracy of 2. a. the applicant sees that a change in weight of 10.000 pounds.000 pounds to 1. TAKEOFF PERFORMANCE BASED METHOD EXAMPLE.000 pounds over the low-weight band. a change of 5.000 pounds/ 2. a change in 5000 pounds of weight in the high-weight band means a 500 foot difference in takeoff distance.71% accuracy at 350.000 pounds / 400 foot change) = ± 1. and for less extreme conditions.7% at 200. Once again.000 pounds in the mid-weight band.14% above 350.500 pounds in the high. continued (2) In the weight range of 250.000 pounds in weight means a change of up to 400 feet in the all-engines-operating takeoff distance across the low-weight to mid-weight bands.16% accuracy at 250.000 pounds to 1. the applicant sees that a change in weight of 10. no wind) takeoff at flaps 5.000 pounds to 0.weight band.5 knot change × (10.5 knot change × (10. This weight offset corresponds to an OBWBS weight accuracy of 2.454 pounds in the low. b. (3) In the weight range of 350..5 knot change × (10.4/11/2008 AC 20-161 Appendix 4 APPENDIX 4. This weight offset corresponds to an OBWBS weight accuracy of 0.000 pounds over the high-weight band.250 pounds or ± 1. This weight offset corresponds to an OBWBS weight accuracy of 2.74 % accuracy at 430.000 pounds/ 2 knot change) = ± 7.000 pounds to 2.37% accuracy at 350.300 pounds after rounding.000 pounds over the low to mid-weight band. the applicant determines from AFM data that at the most extreme all-engines-operating takeoff distance situation.000 to 430.000 pounds.000 pounds to 350. c. no runway slope.4% above 250.75 knot change) = ± 5.52 % above 250.5 knot change in V2 and that this relationship holds across the mid-weight band.000 pounds results in a 2.weight band. d. For an uncorrected (i.5 knot change) = ± 6. 4-4.5 -knot change in V2 in each band are therefore: • ± 1. • ± 1. or ± 5400 pounds with rounding. the applicant can fit a curve across these bands in order to smooth out the discontinuities or jumps in weights at the band edges.000 pounds over the mid-weight band.e.000 pounds results in a 2 knot change in V2 and that this relationship holds across the high-weight band. Page A4-3 .000 pounds/ 2. The OBWBS accuracies that result in at most a 100-foot increase in the all-engine takeoff distance are therefore on the order of: • ± 100 foot change × (5. THE EFFECT OF WEIGHT CHANGE ON TAKEOFF/ACCELERATE-STOP DISTANCE. The OBWBS accuracies that result in at most a ± 1. • ± 1.
are accepted without curtailments or procedural adjustments for OBWBS accuracy. d. Therefore the weight change that results in a 100 foot change to the takeoff/accelerate-stop distances does not set the maximum operational accuracy for OBWBS use without curtailment. f.5 knots (see paragraph 4-2 of this appendix). OBWBS operational accuracies that result in at most a ± 1. The applicant notes that the weight changes in paragraph 4-2 of this appendix that result in a 1.5-knot change in V1 or V2 (see paragraphs 4-2 and 4-3 of this appendix.300 pounds of the actual airplane weight in the low-weight band.5-knot change in V2 will change V1 by more than 1. c.5 knots (see paragraph 4-3 of this appendix).000 pounds the OBWBS operational accuracy needs to be ± 2. OBWBS OPERATIONAL ACCURACY AND OBWBS-MEASURED WEIGHT CURTAILMENT. ± 6. e.5-knot change in V1 will not change V2 by more than 1. the weight change that results in a 1. a.000 pounds / 500 foot change) = ± 1. the applicant concludes that the reported weights from the OBWBS can be used without curtailment for OBWBS operational accuracy as long as the OBWBS-reported weight is within: • • • ± 4.000 pounds in the most extreme takeoff distance situation. whichever is greater. Therefore. respectively). TAKEOFF PERFORMANCE BASED METHOD EXAMPLE. continued • ± 100 foot change × (5. This weight offset corresponds to an OBWBS weight accuracy of 0.5-knot change in V1 does set the maximum operational accuracy for OBWBS use without curtailment. g. b. The applicant notes that the weight changes in paragraph 4-4 of this appendix that result in more than a 100 foot change in takeoff/accelerate-stop distance all result in less than a ± 1. 4-5.29% above 350. Therefore.000 pounds of the actual airplane weight in the mid-weight band.4/11/2008 AC 20-161 Appendix 4 APPENDIX 4.000 pounds to 0. the required OBWBS weight accuracy can be expressed in terms of the ratio of these weight uncertainties per band to the actual airplane weight in that band.5-knot error or change in V1 or V2. the weight change that results in a 1. Page A4-4 .23% accuracy at 430. ± 5.000 pounds over the highweight band.5-knot change in V2 does not set the maximum operational accuracy for OBWBS use without curtailment. at an actual weight of 200.4 % to use the reported weight without operational curtailment for OBWBS accuracy. In general. Therefore.000 pounds of the actual airplane weight in the high-weight band.15 % to use the reported weight without operational curtailment. For example. The applicant notes that the weight changes in paragraph 4-3 of this appendix that result in a 1. and for an actual weight of 430. or a 100 foot increase in takeoff or accelerate-stop distance.000 pounds the OBWBS operational accuracy needs to be ± 1.
• ± 2. k. Then the applicant knows that operational conditions such as configuration changes..5-knot change in V1. if the measured OBWBS system accuracies in these weight bands exceed the weight accuracies resulting in no more than 1.500 pounds of additional uncertainty about the actual airplane weight in the high-weight band.4/11/2008 AC 20-161 Appendix 4 APPENDIX 4. This example illustrates the importance of the OBWBS system accuracy.000 pounds of the actual airplane weight in the low-weight band.5 -knot error or change in V1 or V2. • ± 2. Page A4-5 . continued h. • ± 3. wind gusts and winds. V2 and takeoff/accelerate-stop distances. the applicant determines the OBWBS system accuracy by obtaining weight and CG measurements from the aircraft while it sits on precision aircraft scales within a controlled environment such as hanger. 4-6. in general. per the guidance in paragraph 2-2. Now. can result in up to the following weight errors before the need to curtail the weight and CG envelope for the operational accuracy of the OBWBS: • ± 3.d(3) of this AC. This example shows how an applicant can map out an analysis approach to systematically consider the effect of weight changes on V1. j. or a 100 foot increase in takeoff or accelerate-stop distance. l. Alternatively. TAKEOFF PERFORMANCE BASED METHOD EXAMPLE.000 pounds of additional uncertainty about the actual airplane weight in the mid-weight band. Suppose for example the OBWBS-reported weight during the system accuracy testing is within: • ± 1. i. the OBWBS cannot be used without curtailment for OBWBS accuracy at any time. a. etc. the larger the operational environment within which the applicant may use the OBWBS system weight measurements without curtailment for OBWBS accuracy. This analysis determines the operational accuracies that result in at most a ± 1.500 pounds of the actual airplane weight in the high-weight band. The better the system accuracy.300 pounds of additional uncertainty about the actual airplane weight in the low-weight band. passenger movement. CONCLUSIONS. temperature changes.000 pounds of the actual airplane weight in the mid-weight band. and • ± 3.
The analysis method shown in this example can be readily modified to consider the effects of pressure altitude.4/11/2008 AC 20-161 Appendix 4 APPENDIX 4. whichever is greater. and runway slope. when determining the relationship of change in weight to change in takeoff/accelerate-stop distance. or more than a 100 feet increase in takeoff or accelerate-stop distance.5 knot error or change in V1 or V2. continued whichever is greater. which can be accepted without curtailments or procedural adjustments for OBWBS accuracy. OBWBS operational accuracies that result in greater than ± 1. require appropriate curtailment for OBWBS accuracy. b. TAKEOFF PERFORMANCE BASED METHOD EXAMPLE. Page A4-6 . as appropriate. outside air temperature. winds.
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