Appendix 2
(4) Plot each data output parameter in EU versus decimal units.
d. Input. A piece of information required to begin a procedure. During a procedure, inputs are intended to be used or manipulated to achieve a desired output.
e. Interface control documents (ICD).
(1) Data mapping documents that explain the wiring configuration of internal and external DFDRS component interfaces. All source system signals are sent to the recorder.
These signals are traced internally to the final recording format. Every make, model, and series of aircraft has a related series of ICDs for recorded data. For example, a DFDAU ICD describes and defines the electrical interface characteristics and requirements of the line replaceable units (LRU) to the DFDAU.
(2) Data mapping documents contain expected signal input and output information for each recorded parameter type, which can be any of the following ARINC Specification 429 signal formats:
(a) Analog data bit,
(b) Discrete data bit,
(c) Coded discretes,
(d) Binary representation,
(e) Digital BCD, or
(f) Digital encoded parameter.
(3) Other information includes the parameter type, word, subframe, location of the bit(s) in the word (word structure), and total number of bits used in the word. This document may be used to obtain inputs for Procedure A (see section 3).
f. Number of bits. The number representing how much space is required to store the data in a digital word. This number can range from 1 to 12 per ARINC Characteristic 717. If a parameter resolution is not identified, then this number is critical to the useful effectiveness of this appendix. To determine the resolution by assessing the number of bits, see paragraph 2.j below.
g. Output. A piece of information obtained after the completion of a procedure. The outputs produced may be used as inputs for another procedure.
h. Parameter detail document (PDD). Digital parameter specific information. Like a DFDR ICD, this document may be used to obtain inputs for Procedure A.
i. Range. A set of functional and numerical values bounded by a maximum and a minimum. As defined by the input data to Procedure A, the functional range may not truly A2-2
--- Appendix 2 reflect the exact range of a particular aircraft operational or performance parameter. This appendix refers to range as the “change in range”, or by the symbol ΔR. For example, if given a range [R1 , R 2 ], then the total change in range is:
ΔR = R 2 − R1
j. Resolution. An EU representation of the least significant bit (LSB) in the word structure.
This LSB is important when calculating the value of a digital binary type parameter. If the parameter resolution is not identified in the input information, then the resolution must be determined. Given the number of bits and the range in EU, a linear resolution can be calculated by using the following equation:
Where, ΔR is the total change in range, derived in paragraph 2.i, measured in EU, and NB is number of bits, the parameter resolution is denoted by:
ΔR res = 2NB )( Note: It is important to document an appropriate number of decimal places (or express the resolution as a fraction) to avoid the introduction and propagation of error.
3. Reverse DFDR data correlation Procedure A. This section describes the first procedure that DFDR test engineers may follow in conjunction with Procedures B and C to develop an acceptable baseline correlation document, when no document exists.
a. Requirements. This subsection identifies the required data items needed to begin reverse engineering the DFDR data correlation document.
(1) Procedure A requires a search for and an identification of parameter specific information. ICDs, PDDs, and conversion documents are resources that contain information to perform Procedure A. The required minimum inputs to conduct Procedure A are conversion algorithms (decimal units to EU), ranges (EU), and either resolutions or number of bits in the digital word.
(2) The following example illustrates how to find ΔR when given a parameter’s range. If the range of the roll attitude parameter is –180˚ to +180˚, then the total change in range, ΔR, is:
ΔR =+180° − (−180°) = 360°
(3) The parameter resolution in EU may not be available from the resource documents.
If the parameter resolution is not identified in the input information, then the resolution must be determined from the number of bits. If roll attitude is the parameter of interest, then the following is an example of how to solve for a linear resolution. Given the number of bits is 12 and the change in range is given in the previous example, the linear resolution can be solved by using the following equation:
A2-3
Appendix 2 ΔR 360 res = = NB(2 ) 4096 res = 0.0879
(4) A conversion document contains the algorithms, tables, or codes to convert applicable parameters from EU to decimal units. This information is critical in completion of reverse data correlation. Depending upon the ARINC Specifica tion 429 data word structure of a specific parameter, an algorithm or conversion equation, a look-up table, or a conversion code is required to perform the conversion. An example of a binary formatted data conversion algorithm is below. In this example roll angle is measured in degrees, such that:
Decimal unit = 0.0000000000001515 ×ϕ 5 + 0.0000000000003167 ×ϕ 4 −
0.0000001424806891×ϕ 3 + 0.0000003524948261×ϕ 2 + 0.1155043360208260 ×ϕ +
0.0046571693139939,
where ϕ denotes the roll angle in EU
(5) Now that the required inputs for Procedure A are gathered, subsection 3.b lays out the foundation to derive baseline correlation data.
b. Process. This subsection outlines the steps to create the baseline of manufacturer system-specific data.
(1) A baseline must be established that translates a 1 to 1 correlation between decimal units and EU for the full range of every parameter. For each parameter, use the conversion algorithm or other method to calculate the full range in decimal units.
(2) Begin plotting the lowest value in the full range against the respected decimal unit.
2NBThen, increment the resolution to obtain decimal unit values for all range values. All 2NB resvalues are plotted with an uncertainty of half the resolution, ± . 2
c. Data application/desired output. This subsection identifies the required data to be produced by following Procedure A.
(1) In Procedure A, DFDR parameter information was gathered to convert the full range from EU to decimal units. The conversion algorithm or other method was utilized to create a baseline of DFDR system data. The baseline co nversion data must be stored or displayed in some documented fashion.
(2) If applicable, the parameter’s resolution must be converted from EU to decimal units.
In the case of a parameter with a non-linear resolution, an EU to decimal conversion must be considered from decimal count to decimal count. Section 5 discusses the significance and applicability of the parameter’s resolution to this appendix.
(3) A baseline plot for an identified parameter.
A2-4
~ ~~ __,. V"" ~ .,,....,,.- ~ ~ ~ _,.,...,-,~ _./ -- --- I-""'"'
J,-
~ 8/17/10 AC 20-141B Appendix 2
(a) One example of displaying the baseline data is by plotting individual data points.
One implementation would be to plot decimal units as a function of EU, with increments of the resolution determined in subsection 3.c. The following linear baseline plot, Figure 2-1, is a continuation of the roll attitude example from previous paragraphs. Figure 2-2 shows an example of a nonlinear baseline plot.
(b) If a baseline plot cannot be established with reasonable accuracy, then ground station tools may be required to perform an accurate baseline plot of intermediate converted values. For example, some DFDRS implementa tions process synchro signals which increases both the complexity and accuracy of a decimal unit to EU conversion.
FIGURE 2-1. EXAMPLE LINEAR BASELINE PLOT OF EU TO DECIMAL UNITS 150 120 90 60 30 0 -16 -12 - 8 - 4 -30 0 4 8 12 1 6 -60 -90 -120 -150 Roll Attitude Parameter Conversion Data 180 -180 Decimal Units Engineering Units -20 A2-5 20
~ .......
/ V ~ ~ _....,..,,..
~~ / .......
40000 30000 20000 10000 0 0 -10000 200 4 00 600 800 1000 1200 1400 8/17/10 AC 20-141B Appendix 2 FIGURE 2-2. EXAMPLE NON-LINEAR BASELINE PLOT OF EU TO DECIMAL UNITS Electric Coarse Altitude Parameter Conversion Data 50000 Engineering Units -200 1600
(4) Once data storage or display is complete, this information is used in section 5 as a baseline to determine compliance with the CFR.
4. Reverse DFDR data correlation Procedure B. This section identifies the data items needed to complete the required aircraft test of DFDR data reverse correlation. Accomplishing this procedure depends on the availability of the aircraft to be tested.
a. Requirements. Procedure B requires the data ranges for each parameter, a DFDRS-equipped aircraft, and all equipment necessary to test the onboard DFDRS. The decimal unit to EU conversion algorithm or method is required. The operator or test engineer must have a predetermined list of data points to test for each parameter through the static and full dynamic ranges. This list of data points must be in EU and correlate to one of the 2NB data points obtained in Procedure A. It is also useful to have a tool capable of converting conventional forms of digital outputs into decimal units.
Note: There are cases where certain types of parameters cannot be tested in the airplane environment. These parameters can only be stimulated in a lab environment and applied to the airplane through analysis. For example, a computer failure can be simulated in the lab environment and the software paths of the acquisition unit can be confirmed. This testing can be applied to the airplane where it is rare that one can force working equipment to fail for test purposes. Credit should be given that source systems that provide data to the acquisition unit had these functions tested during their certification.
Decimal Units A2-6
Appendix 2
b. Process. The test engineer evaluates the DFDRS recorded data based on the data ranges for each parameter.
(1) The test engineer must use the predetermined list of data points to be recorded as identified in section 3.
(2) By controlling the aircraft input, the conventional form of the digital output is to be recorded.
(3) The conventional form of the digital output must be converted into decimal units. A capable tool (i.e., calculator, computer application, etc.) makes this conversion easier.
c. Data application/desired output. This paragraph identifies the required data to be produced by following Procedure B.
(1) The parameter’s static and full dynamic ranges and recorded outputs should be stored or displayed. Use a method similar or comparable to that used in Procedure A (i.e., plot EU as a function of decimal units).
(2) Once data storage or display is complete, this information is used in section 5 to compare against the baseline to determine compliance with the CFR.
5. Reverse DFDR data correlation Procedure C. This section outlines the process to determine compliance with the CFR. It defines a comparative assessment between actual aircraft measured data and manufacturer system-specific data. If regulatory compliance is not determined, then the operator must choose to repair, recorrelate, or replace the noncompliant system. Procedures A and B must be accomplished before completing Procedure C.
a. Requirements. This subsection identifies the required data items needed to accomplish DFDR data reverse correlation. The recorded conversion data from Procedures A and B are required to begin Procedure C. If applicable, the parameter’s resolution from Procedure A is also required and is critical in determining an acceptable parameter correlation.
(1) Procedure A contributes manufacturer-specific system conversion and parameter information. For each parameter, a baseline with digital tolerances was established. If applicable, an EU to decimal unit representation of expected DFDR system operational performance was created. In the following paragraphs, data obtained from Procedure A will be referred to as “expected” data.
(2) Procedure B contributes aircraft-specific DFDR data from testing the static and full dynamic range of each parameter. The number of data points recorded is discretionary; greater numbers of data points increase the probability of the parameter being in compliance. The actual data stored in an aircraft’s DFDR needs to be verified through a comparative assessment with the data from Procedure A. In the following paragraphs, data obtained from Procedure B will be referred to as “measured” data.
b. Process. This subsection outlines the steps to complete the analysis and to determine compliance.
A2-7
Appendix 2
(1) Once the data from Procedure A and B are present, a comparative assessment is required. This analysis relates an aircraft-specific DFDR operational performance to the expected DFDR operational performance as documented by the system manufacturer.
Note: We recommend use of a graphing program with the capability to calculate “R” numbers. It is useful to plot the measured data points on the expected baseline graph. An “R” numbe r should be produced to read 0.99 or greater in order to achieve regulatory compliance.
(2) First, select the EU values for which there are both expected and measured data.
Then, obtain the decimal unit values for each data pair. Use the following statement to compare the decimal unit values for the expected and measured data. This comparative analysis must be done for each parameter’s operational range.
(3) If the measured data, denoted as Xm , is within the expected data plus or minus half resthe resolution, denoted as X ± , then the parameter data value is known with 100 percent e 2 certainty to be in compliance. This statement is represented mathematically by res resX − ≤ X ≤ X +e m e 2 2
c. Data application/desired output. This paragraph provides recommendations and information based on the conclusions from the analysis in subsection 5.b. The analysis in subsection 5.b concludes that:
(1) The design is in compliance with applicable sections of 14 CFR,
(2) The system relating to the applicable parameter sensor needs to be recalibrated, or
(3) The parameter must be recorrelated.
d. Ensure compliance. The final step is to ensure that the parameters with measured data not within the expected data limits are in compliance. To reach conclusion in paragraph 5.c(2), the data must be analyzed and a consistent discrepancy must be identified between the measured and expected data values. While the applicable system is in a neutral state, adjust to within the limits. The conclusion in paragraph 5.c(3) is a result of random inaccurate trends identified in the comparison analysis. The applicable system needs to be repaired, or replaced.
A2-8
START YES NO YES NO YES NO YES END Not required to carry an FDR YES NO YES NO YES NO YES NO Page A3-2 § 91 .609 Page A3-3 § 121.344 Page A3-6 § 125.226 Page A3-8 § 135.152 8/17/10 AC 20-141B Appendix 3 APPENDIX 3. DIGITAL FLIGHT DATA RECORDER PARAMETER
REQUIREMENTS FLOWCHART
FIGURE 3-1. FLIGHT RECORDER PARAMETER REQUIREMENTS A3-1
Appendix 3 FIGURE 3-2. PART 91 FLIGHT RECORDER PARAMETER REQUIREMENTS § 91.609
A Multiengine turbine pwr’d?
YES Fractional ownership under §91.1045?
YES Aircraft type NO 10 or More Passengers?
NO NO Manufactured after 10/11/1991?
YES END Not required to carry an FDR NO Must comply with §91.609(c) & Appendix E 18 Parameters Manufactured after 10/11/1991?
YES Airplane Rotorcraft Rotorcraft More than 30 passenger seats or more than 7500 lb payload?
Airplane B.1 D NO YES Page A3-3 Page A3-8 END From Page A3-1 Must comply with §91.609(c) & Appendix F 23 parameters §121.344 §135.152 A3-2
From Page A3-2 §91 .609 No FDAU YES YES NO Page A3-4 §121.343 Di ital FDAU FDAU YES NO YES Page A3-8 §135.152
121.344(e) Appdx M 57 arameters 1·2 §121.344(d) Appdx M 34 arameters 1 §121.344(c) Appdx M. Record 22 parameters 1.
Parameters 12-14, single source allowed.
§121.344(b) Appdx M. Record 22 parameters.
Parameters 12-17, single source allowed .
§121.344(b) Appdx B. Record 17 parameters .
Parameter 18 req'd based on capacity.
§121.344(b) Appdx B. Record 18 parameters.
1 Commensurate with capacity , any other parameters (of 88) that have information sources installed and connected to the recording system.
2 For Boeing 737 airplanes manufactured after August 18, 2000, parameters 88 through 91 are required to be recorded by February 2, 2011.
8/17/10 AC 20-141B Appendix 3 FIGURE 3-3. PART 121 FLIGHT RECORDER PARAMETER REQUIREMENTS § 121.344 A3-3
Appendix 3 FIGURE 3-4. PART 121 FLIGHT RECORDER PARAMETER REQUIREMENTS § 121.343 Manufactured after 10/11/1991?
§121.343(f) Appdx B 29 mandatory and 12 recommended parameters.
NO YES §121.343(d) Appdx B 17 mandatory parameters.
NO B.2 From Page A3-3 §121.344 Has a digital databus & ARINC 717 DFDAU?
Manufactured after 5/26/1989, or type certificated after 9/30/1969?
YES §121.343(c) Appdx B 11 mandatory parameters.
YES NO §121.343(f) Appdx B 29 mandatory and 12 recommended parameters.
END A3-4
NO YES YES Not required to comply with part 121.
>-"-''--I ~ May be required to §121.344a(c) Appdx M 88 parameters .
§121.344a(b)(1) Appdx M 57 parameters 3.
comply with §135.152.
Page A3-8 §135.152 NO >-_N_o __ .. Not required to carry a FDR.
§121 344a(1)(2)(3) 181 or 222 parameters listed in §121.344(a). Ranges, accuracies , and resolutions as specified in part 135 Appndx B.
YES Either parameter listed below must be recorded :
§121.344(a)(12) or (a)(15) §121.344(a)(13) or (a)(16) §121.344(a)(14) or (a)(17) For airplanes with more than two engines , §121.344(a)(18) must also be recorded if sufficient capacity is available on the existing recorder.
Parameters §§121.344(a)(12) through 121.344(a)(17) each may be recorded from a single source.
2 Commensurate with the capacity of the recording system (FDAU or equivalent and the DFDR).
3 Commensurate with the capacity of the recording system, all additional parameters (88) listed in §121.344(a) for which information sources are installed and which are connected to the recording system.
8/17/10 AC 20-141B Appendix 3 FIGURE 3-5. PART 121 FLIGHT RECORDER PARAMETER REQUIREMENTS § 121.344a A3-5