METHOD TO RECOVER NON-RECOGNIZED ERRORS IN AIRCRAFT WEIGHT DETERMINATIONS TO INCREASE WEIGHT AND CENTER OF GRAVITY LIMITATIONS FOR REGULATED AIRCRAFT
20220358517 · 2022-11-10
Inventors
Cpc classification
International classification
Abstract
The method obtaining a change to approved weight limits of a regulated aircraft type comprises the steps of determining a difference between a first maximum takeoff weight limit and a second maximum takeoff weight limit and, using the difference between the first maximum takeoff weight limit and the second maximum takeoff weight limit, identifying the second maximum takeoff weight difference as a percentage of the first maximum weight limit. In other embodiments, a second maximum landing weight limit, a second maximum takeoff weight limit, a second zero-fuel weight limit, and a second maximum ramp weight limit, are each identified as a percentage of the first maximum takeoff weight limit.
Claims
1. A method of obtaining a change to approved weight limits of a regulated aircraft type, wherein a plurality of aircraft of the aircraft type are each capable of carrying a payload and non-payload items, the payload computed using assumed and averaged weight values, the non-payload items based upon indicated weights of the non-payload items, the aircraft type having a first maximum weight limit and a first maximum takeoff weight limit, the method comprising the steps of: a. For one of the aircraft of the aircraft type, using a computer and modeling programs, simulating plural fully loaded aircraft flights operating near the first maximum weight limit, obtaining statistical and probability data of weight ranges, the statistical and probability data of weight ranges being associated with the assumed and averaged weight values of the payload and the indicated weights of the non-payload items, carried by the aircraft; b. Repeating step a) for additional simulated flights, determining an increasing range of assumed payload and non-payload weights; c. For a number of actual flights operating near the first maximum weight limit, obtaining computed data for the assumed weight values of the payload and non-payload items; d. For the same respective actual flights, comparing the range of statistical and probability data of payload and non-payload weight values, to the computed data for the assumed weight values of the payload and the indicated weights of the non-payload items, and determining a weight difference; e. For subsequent actual flights of the plurality of aircraft, using an automated system to measure the respective aircraft total weight, and using the determined weight difference, obtaining a second maximum weight limit for the aircraft type and a second maximum takeoff weight limit for the aircraft type, the second maximum weight limit being more than the first maximum weight limit and the second maximum takeoff weight limit being more than the first maximum takeoff weight limit; f. Determining a difference between the first maximum takeoff weight limit and the second maximum takeoff weight limit; g. For further subsequent actual flights, using an automated system to measure the respective total aircraft weight, while operating the aircraft of the aircraft type at weights within the second maximum weight limit.
2. The method of claim 1, further comprising the step of, using the difference between the first maximum takeoff weight limit and the second maximum takeoff weight limit, identifying the second maximum takeoff weight as a percentage of the first maximum takeoff weight limit.
3. The method of claim 1, the regulated aircraft type having a first maximum landing weight limit, the method further comprising the step of, using the second maximum takeoff weight limit, determining a second maximum landing weight limit.
4. The method of claim 3, the second maximum landing weight limit identified as a percentage of the aircraft first maximum takeoff weight limit.
5. The method of claim 1, the regulated aircraft type having a first maximum zero-fuel weight limit, the method further comprising the step of, using the second maximum takeoff weight limit, determining a second maximum zero-fuel weight limit.
6. The method of claim 5, the second maximum zero-fuel weight limit, identified as a percentage of the first maximum takeoff weight limit.
7. The method of claim 1, the regulated aircraft type having a first maximum ramp weight limit, the method further comprising the step of, using the second maximum takeoff weight limit, determining a second maximum ramp weight limit.
8. The method of claim 7, the second maximum ramp weight limit identified as a percentage of the first maximum takeoff weight limit.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0075] Although the features of this invention, which are considered to be novel, are expressed in the appended claims, further details as to preferred practices and as to the further objects and features thereof may be most readily comprehended through reference to the following description when taken in connection with the accompanying drawings, wherein:
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0090] In the description herein, the disclosures and all other information of my earlier U.S. Pat. Nos. 5,214,586; 5,548,517; 6,128,951; 6,237,406; 6,237,407; 8,180,504; and 8,543,322 are incorporated by reference.
[0091] The present invention utilizes prior art methods to physically measure the weight of an aircraft as it rest on the ground. Parallel measurements of aircraft weight by independent weight sensing features allow for an increase in confidence of the physical weight measurements and further offer cross-verification for physical weight measurement system accuracy.
[0092] The present invention utilizes prior art methods to physically measure the Center of Gravity “CG” of an aircraft as it rest on the ground.
[0093] In today's airline operations, aircraft MTOW determinations are computed by a Load Build-Up Method, which processes and procedures have remained relatively un-changed for the past 50 years. The FAA has published Advisory Circular AC120-27E offering guidance for an approved method to determine the aircraft weight by “computations” which are independent of any requirement to measure of the weight of a an aircraft fully loaded with passengers. The fully loaded weight of the aircraft is computed by a process of compiling the weights of various payload items based upon FAA “designated” average weights, for the varying elements such as passengers, carry-on baggage, checked baggage, crew weight; along with cargo weight and the weight of fuel loaded; onto a previously measured empty aircraft weight. This method of computing the aircraft weight based on the summing of the various weight elements loaded on to a pre-measured empty aircraft weight is often mentioned as the Load Build-Up Method and in this description shall continue to be referred to as the “LBUM”.
[0094] The FAA's AC 120-27E designated weight assumptions/allocations for airline passengers and baggage are:
TABLE-US-00002 Average passenger weight - summer 190.0 lb. Average passenger weight - winter 195.0 lb. Average bag weight 28.9 lb. Average heavy bag weight 58.7 lb.
[0095] On the actual day of a flight, typically two hours prior to the departure of that flight, the flight's automated load planning program will be transferred to the desktop computer display of one of the airline's Flight Dispatchers. It is the responsibility of the Flight Dispatcher to then monitor the planned load of that flight as passengers check-in at the gate. The number of passengers and allocations for checked bags are input to the load-planning program. Typically this process goes without interruption and the aircraft will dispatch on schedule, as planned. As the door of the aircraft is closed and the load-plan is closed-out by the Flight Dispatcher, the “planned load” will always match the “departure load” as submitted to the FAA; because both are based on the same compilation of weight assumptions used in determining the LBUM. Many if not most airlines currently dispatch their aircraft under FAA approved LBUM procedures; a method which helps to keep the airlines on schedule.
[0096] Throughout the description herein, examples will be shown for calculations to determine aircraft take-off weight, being a weight that must never exceed the aircraft's certified Maximum Take-Off Weight (“MTOW”) limitations. Other aircraft weight limitations including MLW and MZFW are computed using a derivative the LBUM. Calculation of the “planned landing weight” is determined by subtracting the weight of the fuel, which is planned to be consumed during the flight from the determined aircraft take-off weight. Calculation of the zero-fuel weight is determined by subtracting the weight of the fuel within all fuel tanks, as indicated by the aircraft's fuel indicators, from the determined aircraft take-off weight.
[0097] Systems and/or components used and installed on Regulated aircraft are conformed and certified by the FAA and other Regulatory Authorities and typically have “design standards” which are stringent up to a factor of 10.sup.−9 and used in qualification. Ten to the minus 9.sup.th (“10.sup.−9”) is the term typically used and has the equivalent of the odds for a failure of no more than one in one billion (1 in 1,000,000,000). When considering the chances or odds of an airline having non-recognized errors in their methods and procedures for determining aircraft take-off weight fall well below the 10.sup.−9 standards.
[0098] With many daily departures and the associated chances for some type of failure within the airline's LBUM system for determining aircraft weight, the illustration utilized (shown in
thus the example (shown in
[0100] The examples shown (in
[0101] An aircraft is typically supported by plural landing gear struts. In many if not most cases, aircraft are supported by three landing gear struts. Each landing gear strut is designed much like, and incorporates many of the features of a typical telescopic shock absorber. The shock absorber of the landing gear strut comprises internal fluids, of both hydraulic oil and compressed gas. More simply said . . . “the weight of an aircraft rests on three pockets of compressed gas.”
[0102] As a point of clarification, throughout this description the use of the word “weight” can often be substituted with the use of the word “load” in that some airline operations will seek to avoid any possibility to allow the LBUM determined “take-off weight” of their aircraft be measured; thus referring to loads being applied onto the landing gear struts are often preferred.
[0103] The invention herein described will have some portion of all aircraft take-off weights measured as part of the defined processes and procedures to allow for an increase in the MTOW, MLW and MZFW limitations; while those airlines not wanting weight determination but instead desire only relief of CG curtailments will use the determination of “load distribution” features of this invention, without the continued calculations to determine the amount of measured aircraft weight supported.
[0104] The average population weight has been documented as becoming heavier year-after-year. For this reason, filled aircraft will (if measured) have a heavier measured weight than the weight computed by population weight data determined in the current FAA/AC120-27E, issued Jun. 10, 2005; which is in use today. Airlines throughout the United States are using this stale weight data in the current 28,537 aircraft dispatches per day.
[0105] By measurement of just the loads applied to each landing gear strut and thus transferred as pressure within each landing gear strut, with the further comparison of the load distribution between the combined main landing gear to that of the nose landing gear, the aircraft CG is established, without measuring the weight of the aircraft.
[0106] The weight of the aircraft supported by the above mentioned pockets of compressed gas is transferred down the landing gear strut to the landing gear axles, which bear the load and are supported by the landing gear tires. As weight is added to the aircraft, the axles will bend and deflect with the addition of more load. As an alternate means of determining aircraft weight, the bending/deflection of the aircraft landing gear axles can be monitored and measured with such axle deflection being directly proportional to the additional amount of weight added. The deflection of the landing gear axles represent the same load as supported by the pockets on compressed gas, thus both provide methods of determining aircraft weight, which may run parallel.
[0107] This invention provides methods of identifying, defining and illustrating a means of justification, for aviation Regulatory Authorities to allow for increases to the weight limitations for Regulated aircraft. The methods described herein develop various strategies including the building of a “justification basis” for increases to MRampW, MTOW, MLW and MZFW limitations; to higher weight limitations, which approved increased weight amounts are less than the amount of non-recognized weight errors in existing operations using the FAA approved guidance of AC120-27E.
[0108] Use of prior art aircraft weighing systems are implemented into a Regulatory Authority approved schedule to periodically make aircraft take-off weight measurements, along with unique methods and procedures for the review, analysis and documentation of non-recognizes weight errors, currently allowed in LBUM procedures; which will provide the necessary evidence for Regulatory Authorities' granting weight increases in amounts not exceeding the non-recognized weight errors being allowed today, through a Regulatory Authority's finding of an Equivalent Level Of Safety.
[0109] The methods of this new invention further develop strategies for new requirements, for implementation of operational procedures to assure Regulatory Authorities; that allowing the increase in MRampW, MTOW, MLW, and MZFW limitations for Regulated aircraft, will offer an Equivalent Level Of Safety, as an alternative means of Regulatory Compliance.
[0110] Regulatory Authorities do not require airlines to weigh aircraft to determine aircraft take-off weight, as a means to confirm aircraft weight limitations have not been exceeded. The procedures implemented in this invention for a defined schedule of pre-take-off aircraft weighings, facilitate the development of a new category of “reliability program” implemented to assure Regulatory Authorities that any increase in aircraft weight limitations shall not be abused nor exceed the non-recognized weight errors currently being allowed. Such periodic fully loaded aircraft take-off weighings will create a Superior Level of Safety, to that of aircraft currently operating with un-measured weights, which un-measured weights allow even further exceedance, beyond of certified weight limitations.
[0111] The present invention offers apparatus and methods utilizing a variety of sensors for collecting landing gear load data to continually update a variety of interrelated computer software programs, creating a more advanced aircraft weight measuring system.
[0112] To summarize this system, apparatus and methods used for continuous monitoring and measuring by various sensors include: [0113] Strut pressure/temperature sensor [0114] Landing gear strut axle deflection sensor [0115] Aircraft inclinometer [0116] On-aircraft computer to collect aircraft and landing gear data [0117] Off-aircraft computer to process collected landing gear data, with software functionality to determine aircraft weight and CG [0118] Wireless communication capabilities between on-aircraft computer and off-aircraft computer
[0119] It is important for any aircraft weighing system to have the ability to accurately determine the aircraft weight before the departure from the gate.
[0120] This invention provides methods of identifying, defining and illustrating various means of justification for aviation Regulatory Authorities to allow for increases to the certified aircraft weight and operational CG limitations for Regulated aircraft. The methods described herein develop various strategies in the identification of non-recognized weight errors for a justification basis built upon the statistical demonstration of the long history of these non-recognized weight errors having created no un-safe aircraft operations for fully loaded/weighted aircraft, and to further construct an acceptable reliability program of safe aircraft operations with weight increases in Regulated aircraft weight limitations, equivalent to the non-recognized weight errors currently allowed today.
[0121] Airlines welcome any opportunity to increase the payload capabilities of their aircraft, considering the opportunity to increase the MTOW and associated MLW and MZFW limitation by up to 5,960 pounds and 3.4% of the MTOW (shown in
[0122] In the preferred embodiment, the method for obtaining a Regulatory Authorities' approval for an increase in the aircraft MTOW and associated MRampW, MLW and MZFW limitations includes the following steps: [0123] 1. Record daily determinations of the total “computed” weight of the aircraft using existing weight determination procedures provided in the LBUM process (for example, shown in
[0135] A question still remains; “Why not just used measured aircraft weight and CG for every dispatch?”
[0136] As previously mentioned; “As good as an OBWBS might be for measuring the aircraft weight, such a system cannot plan the aircraft load.” Airlines attempt to avoid any situation where a discovered discrepancy in the aircraft weight or CG, identified by use of a measured aircraft weight, might result in a schedule delay. Thus the development of a “Weight and CG Reliability Program” to allow Regulatory Authority's the assurance that the aircraft is being operated as safe as the aircraft has historically been operated while transporting the non-recognized weight errors; and with increase MTOW equivalent to the non-recognized errors historically allowed, will allow for the airline to proportionally increase the weight transportation capabilities of their aircraft.
[0137] Regulatory Authorities may choose to limit the amount of MTOW increase, to allow only some smaller percentage of the non-recognized weight errors, with airlines are using the “Weight and CG Reliability Program.” Airlines may consider the additional benefits of having the full percentage of non-recognized weight errors added to the MTOW if they immediately begin using measured weights and CG to dispatch their aircraft, and deal with any potential schedule disruptions if the measured aircraft weight is found greater than the increased MTOW limitation.
[0138] Though any of the methods herein described may be used, with potential variations in overall accuracy of the weight determination; the preferred method is to use OBWBS to determine weight supported at each landing gear strut.
[0139] The methods described herein are applicable as procedures and practices used to obtain Regulatory Authority approval to amend existing aircraft weight calculation practices for determining varieties of aircraft weights including: MRampW, MTOW, MLW and MZFW. Referring now to the drawings, wherein like reference numerals designate corresponding parts throughout the several views and more particularly to
[0140] Landing gears 3, 5 and 7 distribute the weight of aircraft through tires 9, which in this illustration rest atop of a platform weighing scale 13, with platform weighing scale 13 resting on the ground 14. Each of scales 13 measure a portion of aircraft 1 weight, supported at each respective landing gear, and with the three scale 13 weight measurements added together, they identify the total weight of aircraft 1 in this example at 176,100 lbs., being 1,900 lbs. (or 1.09% of MTOW) in excess of the certified MTOW of 174,200 lbs. for this Boeing 737-800 aircraft. Aircraft 1 has a forward baggage compartment 15 and an aft baggage compartment 17.
[0141] Electronic elements which are used in this invention, and are attached to aircraft 1, are an on-aircraft data acquisition computer 19, aircraft inclinometer 21 to correct measured aircraft angle of inclination to that being level with the horizon, cockpit display/keypad 23 allowing pilots a means to read on-aircraft computer 19 information and allow pilots to input data into on-aircraft computer 19, landing gear strut pressure sensors 51 and landing gear axle deflection strain gauge sensors 53 (shown in
[0142] On-aircraft computer 19 is capable of wireless communication with a corresponding off-aircraft computer 39 which is located within a building 41. Off-aircraft computer 39 has no aircraft or landing gear sensor inputs. Off-aircraft computer 39 receives, sensor input data recorded by on-aircraft computer 19 via wireless communications. Regulatory Authority's certification of software is required within any computer permanently attached to the aircraft 1. Use of on-aircraft computer 19 to only measure and record sensor data, and make no sophisticated calculations or computations; to then subsequently and wirelessly transmit only the recorded and date/stamped sensor data to off-aircraft computer 39 which does not reside on aircraft 1, can allow for a significant reduction in the system's software certification costs associated with providing airlines with this information. As an example: aircraft On-Board Weight and Balance Systems (“OBWBS”) require Regulatory Authority certification for any internal software. Ground based computers that determine the same aircraft weight and balance information require far less stringent levels of software certification.
[0143] 100% of the weight of the aircraft rest upon the combined left and right main landing gears 5, 7 and nose landing gear 3. The aircraft Center of Gravity (“CG”) 27 can be determined by the comparing the measured weight (or if weight measurements are to be avoided, measured load as identified by strut pressure or axle deflection) supported by the combined main landing gears 5, 7 to that of the measured weight supported by the nose landing gear 3. As the percentage of the weight supported by nose landing gear 3 changes in relation to the weight supported by the combined main landing gears 5, 7; so does the location of the aircraft CG 27.
[0144] Vertical dotted line 29 illustrates the forward end of aircraft 1. Horizontal line 31 illustrates the length on aircraft 1 being 1,554 inches long.
[0145] Downward pointing vertical arrow 35 illustrates the location for weight of aircraft 1, supported by the nose landing gear 3. Downward pointing vertical arrow 37 illustrates the location for weight of aircraft 1, supported by the combined left main 5 and right main 7 landing gears.
[0146] The accurate determination of aircraft 1 CG 27 is a critical process in the load planning for aircraft 1. Though aircraft 1 is 1,554 inches in length as shown by horizontal line 31, the forward and aft limit of the operational center-of-gravity envelope is only 42 inches in overall length, as illustrated by horizontal line 33. With just 42-inches of allowable certified center-of-gravity envelope, airline dispatchers must take great care in determining the amount and specific location of weight loaded onto aircraft 1.
[0147] Typical LBUM loading computations assume all of the bags are loaded and evenly distributed throughout baggage compartment as shown in forward baggage compartment 15. The assumed even distribution of the bags results in the total assumed weight of bags located at the geographic center of forward baggage compartment 15, shown as vertical line 16. The Boeing 737-800 aircraft forward baggage compartment 15 is twenty-five feet in total length, with the forward compartment door 18 located at the center of the compartment 15. The aft baggage compartment 17 is thirty-six feet in length, with the geographic center of aft compartment 17, shown as vertical line 20. Aft baggage compartment door 22 is located near the rear of the aft compartment 17. In this illustration forward baggage compartment 15 has an even distribution of bags, where the assumed weight is assigned to the location at the center of the compartment, as illustrated by vertical line 16. Aft baggage compartment 17 has the concentration of checked bags located in the aft portion of baggage compartment 17, shown by vertical line 24. The LBUM loading computation will not recognize this difference in the location of weight associated with the aft positioned bags in compartment 17, and its non-recognized shift in aircraft CG 27 further aft, as shown by “aft-shift arrow 26”. Both forward and aft baggage compartment are equipped with restraining nets that hold the bags in place, to avoid the bags sliding as the aircraft 1 takes-off. This non-recognized aft loading of the bags could have the aircraft CG 27 located beyond the aft center-of-gravity limit, creating a scenario where the aircraft is too tail heavy in which the aircraft could over-rotate at take-off, then stall and possibly crash. Measured aircraft CG 27 allows for a Superior Level of Safety, in comparison to the approved methods for determining CG 27 today.
[0148] Although the weight of aircraft 1 is shown measured on platform weighing scales 13, the weight of the aircraft can be measured by a variety of OBWBSs (as shown in
[0149] Referring now to
[0150] Referring now to
[0151] Axle deflection sensor 53 will transmit a signal representing the weight applied to the landing gear strut 7, to the system on-aircraft computer 19 (shown in
[0152] Referring now to
[0162] Referring now to
[0163] Regulatory Authority guidance found in AC120-27E shows the average passenger weight has been established from the National Health and Nutrition Examination Survey (NHANES) conducted by the Centers for Disease Control (CDC) in 1999. The NHANES data conducted actual scale weighings of approximately 9,000 subjects. The standard deviation for NHANES survey was 47 lbs. (this value will be used again to generate thousands of randomly selected passenger weights). The NHANES survey data concluded the population with a “mean” average weight for males as 184 lbs. plus 16 lbs. of additional weight was added for carry-on items totaling 200 lbs. The average weight for females was determined at 163 lbs. plus 16 lbs. of additional weight was added for carry-on items.
[0164] In this example illustrates a full flight, where all available seats have been allocated to passengers with an AC120-27E designated average passenger weight of 190 pounds per person, including carry-on baggage. The 190 lbs. passenger weight assumes 50% of the passengers are male and 50% of the passengers are female. The computation for the total passenger weight is the simple equation of 190 lbs.×174=33,060.00 lbs. (shown in box 59).
[0165] Referring now to
[0166] Referring now to
[0167] Regulatory Authorities make another assumption that within each of the 28,537 daily departures, the passenger distribution between male/female will always be 50% male and 50% female. If the distribution varies whereby 73% of the passengers are male and an additional 40 male passengers are 21 lbs. heavier along with the corresponding reduction of 40 female passengers which are 21 lbs. lighter; the non-recognized weight error will increase by an additional 1,680 lbs. (shown in box 71).
[0168] Beginning with this
[0169] Box 73a illustrates the cumulative non-recognized weight error totaling 3,571.93 lbs.
[0170] Referring now to
[0171] This
[0172] A further comparison was made to today's more typical aircraft boardings with only 20% of the passengers boarding the aircraft with their hands empty, and 40% boarding while carrying only one item, plus an assumed 15% deviation applied to the FAA identified 16 lbs. weight allocation for the carry-on items. The conclusions found in this illustration a potential carry-on weight up to 3,841.7 lbs. (shown in box 77). A comparison of the carry-on bag weight assumption in box 75 to the potential carry-on weight value in box 77 illustrates an additional 1,058.0 lbs. for non-recognized weight error (shown in box 79).
[0173] Box 73b illustrates the cumulative non-recognized weight error increasing to 4,629.8 lbs.
[0174] Referring now to
[0175] Box 73c illustrates the cumulative non-recognized weight error increasing to 5,981.0 lbs.
[0176] Referring now to
[0177] Box 73d illustrates the cumulative non-recognized weight error increasing to 6,797.0 lbs.
[0178] Referring now to
[0180] Scale accuracy typically range with a 0.25% error in the amount of the full weight capability of the scale. Typical platform weighing scales have a maximum weight limitation of 60,000 lbs., thus a 0.25% error would tolerate up to 150 lbs. of error for each scale. While weighing an aircraft, the aircraft must be supported by at least three points. Multiplying by three the 150 lbs. scale tolerances illustrates the 450 lbs. error (shown in box 89).
[0181] Regulatory Authorities allow airlines with large fleets of common aircraft types to avoid having to weigh every aircraft in their fleet on the required 3-year intervals. A large domestic air carrier operates a single fleet type of totaling 450 of the Boeing 737-700 aircraft. AC102-27E prescribes the minimum number of aircraft whose weight shall be measured in determining the “average aircraft fleet weight” is defined as a minimum of 6 aircraft, plus 10% of the remaining fleet. The equation for this numbers is: 6+[(450−6)×10%]=50.4 which is rounded up to 51 aircraft. A rotation of 51 separate aircraft, within the common fleet type, must be re-weighed within 3-year intervals. AC120-27E also requires that no aircraft within the fleet shall be allowed to operate with an OEW which is heavier than 0.5% of the fleet average weight. AC120-27E allocated no weight error in OEW for aircraft contained within an average fleet weighing program. The additional non-recognized 0.5% weight error applied to the Boeing 737-800 OEW of 91,108 lbs. is 455.5 lbs. (shown in box 91).
[0182] Box 73e illustrates the cumulative non-recognized weight error increasing to 7,364.9 lbs.
[0183] In creating a justification basis for Regulatory Authority allowance for the non-recognized weight errors to be allowed as additional weight to the MRampW, MTOW, MLW and MZFW; the Regulatory Authorities must be assured that no other weight errors be allowed in the process for determining aircraft weight. Use of an aircraft weight measuring devise, whether it be ground scales with a typical error of 0.25% or a system permanently attached to the aircraft with typical errors no more than 1.0%; can assure Regulatory Authorities that the non-recognized weight errors can be reduced to errors no larger than those errors in the devices which physically measure the fully loaded aircraft total weight.
[0184] The subtraction of the 1,742.0 lbs. (shown in box 93) being the 1.0% error associated with the aircraft weighing device, measuring up to the 174,200 lbs. MTOW limitation of the Boeing 737-800 aircraft, from the total non-recognized weight errors of 7,364.9 lbs. (shown in box 73e) equates to a potential weight increase of 5,622.9 lbs. (shown in box 95) to the MTOW. 5,622.9 lbs. divided as a percentage of the 174,200 lbs. total aircraft weight equates into a 3.2% increase in the MTOW for the Boeing 737-800. The use of an aircraft weight measuring device to eliminate any non-recognized weight errors in excess of weight error associated with the aircraft weight measuring device creates a justification basis for an Equivalent Level of Safety for a Regulatory Authority to allow a MTOW increased weight equivalent to the net difference between the non-recognized weight errors, and the aircraft weight measuring devices error tolerances.
[0185] Today's modern aircraft are developed through “generational design criteria.” Different eras of generational aircraft began with the cloth fabric covered bi-wing design of the Wright brothers first aircraft. A subsequent generational design began with use of aluminum structural components and a single wing and rear stabilizer. A later generational design came with the jet engine; followed by today's modern aircraft having jet engines with swept-wings, allowing for greater speeds, thus carrying more weight. More simply said, an aircraft of a specific generation is often scalable. Scalable to the point the aircraft design can be expanded and enlarged by keeping all the generational design features “proportionally aligned.” This allows for a shorter period for design build-up, in the development and certification of a new aircraft, with either smaller or larger sizing percentages.
[0186] This also transitions to the weight limitations for aircraft within a specific generational design, being similar. As an example: the Maximum Take-Off Weight “MTOW” (being 100%), with maximum landing weight (being 82% of MTOW), and empty operating weight (being 52% of MTOW). Thus, the appeal for identifying the amount for non-recognized weight errors for a particular aircraft model (with the example shown herein a Boeing 373-800) as a percentage of the MTOW.
[0187] When comparing the value for each of the different weight limitations associated with: MTOW, MLW, MZFW; the amount of non-recognized weight errors is a fixed amount; thus, when the OBWBS demonstrated accuracy (in this example 1% of MTOW) is subtracted from the value associated with the non-recognized weight errors, and compared as a percentage of the MTOW (described above as 3.2%) will be a different percentage when compared to MLW (3.8%) and MZFW (4.1%) and shown below:
TABLE-US-00003 Boeing 737-800 Non-recognized weight errors 7,364.9 4.2% MTOW OBWBS demonstrated accuracy −1,742.0 1.0% MTOW Recoverable weight - fixed amount 5,622.9 3.2% MTOW Maximum Take-Off Weight 174,200.0 3.2% MTOW Maximum Landing Weight 146,300.0 3.8% MLW Maximum Zero Fuel Weight 138,300.0 4.1% MZFW
[0188] The percentage values for recoverable weight, illustrated in this example may change slightly, due to variations in the demonstrated accuracy of a particular OBWBS, and/or the non-recognized weight errors may be found different than those shown in the initial statistical modeling. An example of a significant change in the non-recognized weight errors occurred during the period just prior to Jun. 12, 2021; when airlines were using the old FAA AC120-27E established average passenger weight of 195 pounds. A deadline of Jun. 12, 2021; was established for airlines to complete surveys and implement their revised average passenger weights, which found the average passenger weight at 208 pounds. Multiplying the additional 13 pounds by the 174 passengers on the Boeing 737-800, would have the non-recognized weight errors increasing by an additional 2,262 pounds, beyond the 7,364.9 pounds shown above.
[0189] The FAA has established guidelines related to aircraft Onboard Weight and Balance Systems (“OBWBS) and methods for determining accuracy with the issuance of another Advisory Circular—AC No: 20-161, dated Apr. 11, 2008 “Aircraft Onboard Weight and Balance Systems” in which an airline is allowed to use an approved “OBWBS” with demonstrated accuracy within the four (4) acceptable methods to identify accuracy tolerance levels defined within AC20-161. Though the FAA does not specify any precise percentage (“%”) as an accuracy requirement, the 4 methods contained within AC20-161 (briefly described below) can be quickly summarized as: [0190] a. Takeoff Performance Based Method—computations from V.sub.1 and V.sub.2 speed analysis of the Boeing 737-800 aircraft find the accuracy tolerance of ±2%, resulting with the OBWBS's required accuracy at 98%. [0191] b. Specific Operations Method.—Most airlines will not select this method to demonstrate OBWBS accuracy because it creates the most restrictive curtailments of the aircraft's operational envelope' thus the level of OBWBS demonstrated accuracy would need to be 100%, or airlines would be required to curtail or reduce the aircraft manufacture's original weight limitations for the aircraft. [0192] c. Weight and Balance Procedures Method (Load Buildup Method). Though this method, approved in 2008 as an acceptable method for demonstrating OBWBS accuracy; airlines will hesitate in selecting this method to demonstrate OBWBS accuracy, when considering the non-recognized weight errors identified within U.S. Pat. No. 10,089,634 issued Oct. 2, 2018; some 10 years after the establishment of AC20-161 and based upon the statistical and non-recognized weight errors found in current Load buildup Methods, which within this method are only compared against the assumed high accuracy of the Load Buildup Method, which illustrate above can have errors in excess of 4%, resulting with OBWBS's required accuracy at 96%. [0193] d. OBWBS Operational Demonstration Method. Most airlines will select this method to demonstrate OBWBS accuracy, based upon the statistical and non-recognized weight errors found in current Load buildup Methods, which are compared against the OBWBS and further compared against accurate aircraft weighing scales, thus providing the largest potential amount of allowable error for the OBWBS's accuracy demonstration.
FAA Advisory Circular AC20-161: (accuracy determinations, in full detail)
2-3. OBWBS Accuracy Determination Methods.
[0194] a. Takeoff Performance Based Method. [0195] (1) This method examines the influence of OBWBS system and operational weight and balance accuracies on aircraft takeoff performance. OBWBS operational accuracies that result in at most a ±1.5 knot error change in either V.sub.1 or V.sub.2 speed, or a 100 foot increase in takeoff or accelerate-stop distance, whichever is greater, are accepted without weight curtailments for OBWBS operational accuracy. OBWBS operational accuracies that result in greater errors than these require appropriate curtailment. [0196] (2) From the minimum value of V.sub.1 to the maximum value of V.sub.2 speed, determine the size of the weight error that results in at most a ±1.5 knot change in V.sub.1 or V.sub.2 speed, or a 100 foot increase in the takeoff or accelerate-stop distances, whichever is greater, for the full range of takeoff weights. [0197] (3) These errors may be used to determine a corresponding operational weight accuracy for a given takeoff weight. This operational weight accuracy is used to determine CG accuracy. [0198] (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. For example, assume the OBWBS operational accuracy results in at most a ±1.5 knot change in V.sub.1 or V.sub.2 speed, or a 100 foot increase in the takeoff or accelerate-stop distances, whichever is greater, over a specific range of wind gust or wind velocities for a given temperature day and given takeoff weight. 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. [0199] (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 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.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. [0200] The OBWBS measured weight±weight operational accuracy results in no more than a±1.5 knot change in V.sub.1 or V.sub.2 speed, or a 100 foot increase in the takeoff or accelerate—stop distances, whichever is greater, and [0201] The OBWBS measured CG position±CG position operational accuracy remains within the takeoff limits of the CG envelope. [0202] (6) If the cumulative OBWBS operational accuracy does not meet the criteria of paragraph 2-3.a(5) of this AC, the OBWBS results must be curtailed for operational accuracy before using them for takeoff [0203] (7) The operator should use an actual takeoff weight corresponding to the measured weight plus weight operational accuracy, and the most adverse CG position corresponding to the measured CG position plus or minus the operational CG accuracy. The operator may need to remove or shift payload to keep these values within the weight and balance envelope. See appendix 4 of this AC for an example of this method applied to a B767-300ER.
b. Specific Operations Method.
[0204] 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.e., weight and/or CG envelope curtailments). Operational accuracy levels, expressed as maximum weight, and CG errors experienced are then applied as curtailments to the original manufacturer's envelope, as published in the type certificate data sheet, AFM/AFMS, or weight and balance manual. This method offers the smallest hurdle to determination of an envelope for OBWBS operation, but will typically result in the largest curtailments when compared to the other methods offered. [0205] (1) To demonstrate the OBWBS operational accuracy, you should: [0206] Establish the proposed range of operational and environmental conditions in which the OBWBS will operate. These conditions determine the content of the limitations and conditions as described in paragraph 2-9 of this AC. [0207] Ground test the OBWBS under each of the conditions identified in the limitations and conditions as described in paragraph 2-9.a of this AC. You can use analysis as an alternative to testing if you can substantiate the analysis approach. [0208] For example, suppose the aircraft manufacturer provides environmental or operational limitations, or procedures, that ensure the airplane always operates within the certified weight and CG envelope. Your OBWBS installation may operate within those same restrictions without demonstration. [0209] (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. Weight and Balance Procedures Method (Load Buildup Method).
[0210] 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. These procedures, also known as load buildup methods, have acceptable accuracies as proven in past service experience. 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. 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. Curtail the limits of the CG envelope for any OBWBS operational accuracy that is worse than the accuracy of the load buildup method. [0211] (1) Assess the load buildup method's operational accuracy by considering a variety of factors recommended by the aircraft manufacturer and AC 120-27E, Aircraft Weight and Balance Control, as guidance material. See
FIG. 1. FACTORS TO CONSIDER FOR LOAD BUILDUP METHOD.
[0212]
TABLE-US-00004 Effect on Effect on Factor Weight CG Scale accuracy during reweigh X X Fuel quantity indicating accuracy X X Allowable weight/CG variation prior to X X “reestablishment” of operational empty weight (or allowance for potential variation due to use of fleet weights) Variation in catering/provisioning X X Variation in male/female ratio X X Passenger weight variation X X Crew weight variation X X Baggage weight variation X X Cargo weight variation X X [0213] (2) Tolerable errors associated with each factor are as follows: [0214] (a) Scale accuracy for reweigh—Typically 0.2% of basic empty weight (BEW), based upon reported scale accuracy for analog scale systems or 0.1% of BEW for digital scale systems. Analog accuracy value may be used for aircraft for which the aircraft OEM guidance does not recommend or require the use of digital scales. [0215] (b) Fuel quantity indicating accuracy—Typically 3% of full capacity. [0216] See: [0217] SAE AS-405C, Fuel and Oil Quantity Instruments, dated July 2001, or the most current revision; [0218] Military document MIL-G-8798, General Specifications for Fuel-Quantity, Capacitor-Type Gage System, dated Sep. 30, 1992, or the most current revision, or [0219] MIL-G-26988C, General Specification for Liquid Quantity Gage, dated Sep. 28, 1995, or the most current revision. [0220] (c) Operational Empty Weight Variation—½ of one percent of the mean aerodynamic chord (MAC) and ½ of one percent of maximum landing weight, as outlined in AC 120-27E. [0221] (d) Variation in catering/provisioning—Amount of variation that could be expected to exist, undetected, in galley provisioning. Typically, 20% of the standard galley stock or galley cart weights. [0222] (e) Variation in male/female ratio—Amount of variation in ratio of male to female passengers permitted without adjusting passenger weights in use, typically 10% deviation from ratio upon which passenger weights were based, as outlined in AC 120-27E. [0223] (f) Passenger weight variation—Typically a 1% variation in passenger weight plus a 2% variation in carry-on baggage and personal item weights, defined as tolerable error by AC 120-27E. [0224] (g) Crew weight variation—Typically a 25% variation in the standard crewmember weights, or that amount found to be justified based upon sampling or survey of crewmember weights. [0225] (h) Baggage weight variation—Typically a 2% variation in baggage weight (including both checked and designed heavy weight bags), as defined as tolerable error by AC 120-27E. [0226] (i) Cargo weight variation—Typically a 1% variation in actual cargo weight verses reported cargo weight, based upon typical scale accuracy. [0227] (3) The items eligible for consideration do not include those which originate from human error factors, such as baggage miscount, incorrect passenger count, omitted cargo weights or omitted jump seat occupants. 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), or demonstrate through analysis or test. You choose which of these methods to employ. [0228] (4) In demonstrating the OBWBS operational accuracy, you should: [0229] Establish the proposed range of operational and environmental conditions in which the OBWBS will operate. These conditions determine the content of the limitations and conditions as described in paragraph 2-9.a of this AC. [0230] Ground test the OBWBS under each of the conditions identified in the limitations and conditions as described in paragraph 2-9.a of this AC. [0231] 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.
d. OBWBS Operational Demonstration Method.
[0232] This method may be used to evaluate OBWBS operational accuracy during revenue service for a trial period, or in non-revenue operation as part of a planned ground test program. [0233] (1) Continue to use the original weight and balance program, as applicable, during the demonstrations with the OBWBS installed for evaluation purposes only. [0234] (2) During a trial period in revenue service, the current load buildup system is used as the primary means of performing the weight and balance functions for the airplane and records all OBWBS measurements. [0235] (3) Ground tests can demonstrate equivalent safety between an OBWBS implementation and the current load buildup system by comparing to precision aircraft scale weighing. 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. These differences include load buildup curtailments as described in AC 120-27E, Aircraft Weight and Balance Control, as well as differences in the weights being compared (for example, taxi weight vs. takeoff weight). [0236] (4) In determining the OBWBS operational accuracy, use the OBWBS system accuracy that is at least as accurate as, or better than, the current load buildup system [0237] (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. [0238] (6) Design the demonstration plan to allow multiple tests at multiple airplane weight and CG configurations. 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. Conduct a minimum of twenty five weighing trials. [0239] (7) At least 30% of the tests should be at weights within 10% of maximum airplane takeoff weight; at least 10% of the tests should be at weights within 10% of the minimum airplane takeoff weight; and the tests should cover the aircraft weight and CG envelopes. [0240] (8) Also, test applicable environmental considerations throughout the operating envelope. During a revenue service demonstration, the actual airplane weight can be obtained with a precision scale weighing of the loaded airplane prior to departure.
[0241] Referring now to
[0242] Both on-aircraft computer 19 and off-aircraft computer 39 are equipped with internal synchronized clocks and calendars, to document the time and date of recorded and received sensor data.
[0243] On-aircraft computer 19 has multiple data acquisition/transmission functions which include: [0244] Data Acquisition function “Alpha” which monitors nose and main landing gear internal strut pressure and temperature; and stores the recorded with time and date references to respective strut pressure and temperature measurements to such time as the data is transmitted to off-aircraft computer 39. [0245] Data Acquisition function “Beta” which monitors nose and main landing gear axle deflections; and stores the recorded data with time and date references to respective axle deflection measurements to such time as the data is transmitted to off-aircraft computer 39. [0246] Data Acquisition function “Gamma” which monitors changes the angle of aircraft hull in relation to the level and horizontal ground; and stores the recorded data with time and date references to hull angle change measurements to such time as the data is transmitted to off-aircraft computer 39. [0247] Data Transmission function “Delta” which wirelessly transmits the time and date referenced landing gear sensor data and aircraft hull angle data to off-aircraft computer 39.
[0248] On-aircraft computer 19 is limited to landing gear sensor data acquisitions functions and the transmission of that landing gear load data to off-aircraft computer 39. On-aircraft computer 19 is restricted having operating software which calculates the aircraft weight and CG. Having the sophisticated software to make the calculations for “flight critical information” such as aircraft Weight and CG; operating solely within off-aircraft computer 39, substantially reduces the costs for certifying any subordinate software used in the acquisition of landing gear sensor data, residing within on-aircraft computer 19.
[0249] Off-aircraft computer 39 has capabilities for wireless reception and transmission of multiple landing gear and aircraft hull angle sensor data records and Software packages and data acquisition/transmission functions which include: [0250] Software Program “Zeta” which processes recorded pressure and temperature sensor data from the respective nose and main landing gear to resolve into values equivalent to the weight supported at each respective landing gear, [0251] Software Program “Eta” which processes recorded axle deflection sensor data from the respective nose and main landing gear to resolve into values equivalent to the weight supported at each respective landing gear, [0252] Software Program “Theta” which processes recorded aircraft hull inclination sensor data from the on-aircraft inclinometer to resolve into a value of off-set equivalent to the aircraft being horizontal, [0253] Software Program “Kappa” which re-processes respective landing gear weight values to determine the total aircraft weight and the aircraft CG as compared to weight and CG limitation thresholds. If a weight and or CG threshold is exceeded, notification of such exceedance will be given. [0254] Software Program “Lambda” which receives manual inputs regarding respective LBUM weight and CG determinations to be compared to as Software program “Kappa” weight and CG determinations to develop a data-base to compute the amounts of non-recognized weight errors historically allowed to be transported on the aircraft, [0255] Data Transmission function “Sigma” which wirelessly transmits back to on-aircraft computer 19 the time and date referenced aircraft weight and CG determinations corresponding to the landing gear sensor data processed.
[0256] Referring now to
[0257] The methods on this invention can be extrapolated across the various aircraft weight limitations (MRampW, MTOW, MLW, MZFW) as set by Regulatory Authorities, all of which are determined in some part by the various weight assumptions assigned to male passengers, female passengers, average baggage, heavy baggage and fuel loaded onto the aircraft in various ranges of temperature;
[0258] In this
[0259] With the Aircraft Weight Measuring “System” being used to physically measure the aircraft weight, pilots are assured that a gross weight error will not go un-noticed that might create a safety hazard for a particular flight.
[0260] Upon the computation of a new increased Max Take-Off Weight limitation, predicated on a recognition of the non-recognized weight errors and subsequently measured aircraft take-off weights, and the apparatus to measure and verify take-off weights on all subsequent take-off events, a system support mechanism is created to document the processes, procedures and limitations for the use of the apparatus and methods of this invention, that Regulatory Authorities are assured an Equivalent Level of Safety is maintained. These include, but are not limited to creating and maintaining Instructions for Continued Airworthiness, addition of an Approved Flight Manual Supplement covering this new aircraft weight measuring system operation, limitations and procedures, as well as operational adjustments in the event the aircraft weight measurement system is inoperable.
[0261] Also required is a complete “Documentation of the Justification Basis” for the issuance of an Equivalent Level of Safety, Special Condition, Exemption, or other alternate means of regulatory compliance. These factors include a review of the historical basis of regulatory requirement, along with advancement in technology and operating procedures. Some of these advancements include the development of new systems and procedures that aid pilots in identifying proper aircraft stabilizer and trim settings with systems.
[0262] Continued safe operation of the aircraft will be maintained by the subsequently implemented practice of measured aircraft weight determinations being made from measured landing gear load sensor data, rather than weight assumptions made in AC120-27E. Continued safe operation of the aircraft will be maintained by subsequent monitoring of aircraft operational landing loads, at each respective landing gear.
[0263] These supporting materials, data and procedures are submitted to the Regulatory Authority as justification for the Regulatory Authority's acknowledgement and approval to allow an increase in MTOW, MRampW, MLW and MZFW limitations equivalent to the amount of non-recognized weight errors allowed by AC120-27E assumptions of a variety of weight elements; to increase the aircraft MTOW, MRampW, MLW and MZFW limitations, with this demonstration of an Equivalent Level of Safety, or other qualifying document. An illustration of the extended process design, configured within this initial flow-chart of the methodology for obtaining Regulatory Authority Approval for the allowance to periodically measure aircraft weight, compared to computed weight, to reveal and document the non-recognized weight errors, as the justification basis to increase Regulated aircraft weight limitations herein is shown within
[0264] Referring now to
[0265] Referring now to
Within a prescribed number of flight legs, the aircraft will be return to a maintenance facility for an inspection of the aircraft for signs that flight operating at the increased weight limitations might create additional fatigue damage to the aircraft. If no damage is found, the aircraft will be returned to service. If damage is discovered, the damage will be repaired, and noted into the aircraft's maintenance log. Additionally, the aircraft may have modifications applied to specific areas of the airframe structure to reinforce and correct for potential future fatigue damage, as noticed from the ongoing aircraft inspections. An illustration of this process design, configured within this third flow-chart of the methodology for periodic inspection to insure continued airworthiness of the aircraft will be maintained with the increased MTOW limitation for Regulated aircraft, herein is shown within
[0270] It is understood that aircraft forward and aft CG limitations are defined and set by the Regulatory Authorities, with such forward and aft limitations based on the assumptions of the various weight components being placed at defined and known locations within the aircraft. Upon determination of the amount of allowed weight increase as a percentage of total aircraft weight (as an example: a 4% weight increase to the MTOW), the equivalent percentage increase (the same 4%) shall be applied to the boundaries of the forward and aft CG limitations.
[0271] Described within this invention are methods and strategies developed; in which the whole are now greater than the sum of its parts. Each of the sub-practices of this invention are elements which build upon each other, and strengthen the foundation of justification for the realization that the aircraft design criteria regulations dating back 70 years, have worked well for decades; but the development of new technologies, procedures and the careful implementation and monitoring of such practices offer justification through a finding of an Equivalent Level of Safety, for aviation Regulatory Authorities to allow an increase in the original weight limitations based upon assumed weight values to a second higher weight limitation based upon measure aircraft weight, allow the associated increase to a second set of higher aircraft MRampW, MTOW, MLW and MZFW limitations.
[0272] Where previous systems using assumed weight values have been used as a tool to aid pilots with load planning procedures, to help avoid aircraft departures beyond the aircraft safe operational limits, this new invention uses the apparatus and methods to increase the economic value of the aircraft, by bringing to better light that current Regulations are fall short in the accurate determination of aircraft weight and corresponding aircraft CG; and furthermore by measuring monitoring aircraft weights; allows aircraft to operate at an increased MRampW, MTOW, MLW and MZFW limitations . . . to be at an Equivalent Level of Safety.
[0273] Although an exemplary embodiment of the invention has been disclosed and discussed, it will be understood that other applications of the invention are possible and that the embodiment disclosed may be subject to various changes, modifications, and substitutions without necessarily departing from the spirit and scope of the invention.