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(2) Prior to the filtered flight data final rule publication on February 19, 2010, there was no clarification for the meaning of dynamic condition. Our expansion of dynamic condition was adopted from NTSB safety recommendations A-03-048 through 050. The introductory text to appendix M now states:
“The recorded values must meet the designated range, resolution, and accuracy requirements during dynamic and static conditions. Dynamic condition means the parameter is experiencing change at the maximum rate attainable, including the maximum rate of reversal. All data recorded must be correlated in time to within one second.”
(3) For example, under dynamic conditions, the maximum attainable rate of control surface movement is dependent on the flight control system design of the aircraft. When performing certification testing under dynamic conditions (see definition in appendix 6), the maximum rate attainable includes rates encountered in both normal and abnormal operating conditions. When performing continued airworthiness testing (see functional check definition in appendix 6), it is not necessary to demonstrate the maximum rate attainable under dynamic conditions.
d. What is filtered data? As defined by 14 CFR §§ 121.346(a), 125.228(a), and
135.156(a), flight data is filtered when an original sensor signal has been changed in any way, other than changes necessary to:
(1) Accomplish analog to digital conversion of the signal,
(2) Format a digital signal to be DFDR compatible, or
(3) Eliminate a high frequency component of a signal that is outside the operational bandwidth of the sensor.
Note: Removing noise and aliased signals are industry standard techniques included under paragraph 2.d(3).
e. What is reconstructed data? Reconstructed data is derived from recorded filtered values by applying a unique algorithm to the filtered values. The final rule allows an option to reconstruct filtered data if the recorded DFDR values do not comply with the accuracy requirements in 14 CFR part 121 appendix M (or comparable appendices in parts 125 and 135).
A certificate holder must submit the procedure and the test results that demonstrate an original sensor signal value can be reconstructed from the recorded data.
3. Scope.
a. What parameters are allowed to be filtered? All parameters are allowed to be filtered.
The final rule distinguishes between the following two groups of parameters:
(1) Group 1 – Parameters (1) through (11), (18) through (41), (43) through (87), and (89) through (91). These parameters are allowed to be filtered with no further action.
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(2) Group 2 – Parameters (12) through (17), (42), and (88). If these parameters are filtered, then the operator has two options. These options are discussed in paragraph 3.c(2) below.
b. How to identify if a Group 2 parameter is filtered?
(1) An operator should check its DFDR system engineering and maintenance documentation to determine those parameters that are considered by definition to be filtered.
Wiring diagrams may be necessary to trace the electronic signal from its origin to the DFDAU.
(2) If an operator does not possess the necessary information to determine if a Group 2 parameter is filtered, then the operator may choose to consult the TC, STC, or ATC holder to obtain the necessary information for its aircraft.
c. What are the options if a Group 2 parameter is identified as being filtered?
(1) After a parameter in Group 2 is identified as being filtered, the operating certificate holder must confirm that the accuracy of the parameter is in compliance with 14 CFR part 121 appendix M in both static and dynamic conditions, as specified in the appendix introductory text.
Note: Parameter 42 (power/throttle lever position) is required to be sampled one time per second. The certificate holder may show by quantitative analysis that the filtered data does not affect the parameter’s accuracy.
(2) If the operating certificate holder identifies a filtered parameter not in compliance with the accuracy requirements, the operator has two options. An operator must either redesign the DFDR system to record the original sensor signal, or demonstrate to the FAA that the filtered data can be reconstructed to be in compliance with 14 CFR part 121 appendix M (or comparable appendices in parts 125 and 135). However, if the FAA determines that the reconstruction procedures are not acceptable, then the operator must have the DFDR system redesigned.
4. Compliance times and documentation.
a. What is the compliance schedule?
(1) Operators have 18 months, no later than October 20, 2011 (reporting date), to inspect their DFDR systems and document their findings whether or not their DFDR systems record filtered data for any of the parameters included in Group 2. The operator must create a record of this determination for each airplane on its operations specifications. The operator must maintain this record as part of the correlation documentation required by 14 CFR §§ 121.344(j)(3),
125.226(j)(3), or 135.152(f)(2)(iii). If any of those recorded signals are being filtered, then the operator must identify which parameters are affected. If the parameters are not being filtered, then the operator must document its finding and is not required to take further action, unless a future change is made to its DFDR system.
(2) Operators that report filtered parameters will have two options.
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(a) If an operator chooses to remove the filtering, it has to make the modifications no later than April 21, 2014 (thirty months from the last permissible reporting date).
(b) If an operator chooses to demonstrate by test and analysis that filtered data can be reconstructed, the operator has to submit its reconstruction package, including the procedures and test and analysis results, in the correlation documentation to its FAA certificate holding district office for approval no later than April 22, 2013 (18 months from the reporting date). The final year is needed for the FAA to review the documentation and verify the procedure and test results are repeatable.
(3) In all cases, compliance with the rule is required by April 21, 2014 (four years from the effective date). In no case will the submission of reconstruction procedures and test and analysis results be considered compliance until that submission is approved by the FAA.
Operators who choose that method of compliance are cautioned to submit their procedures and test and analysis results as early as possible in case their submissions fail to be approved and other action is needed.
b. May an operator submit data from the airframe manufacturer? Yes, operators may submit documentation from airframe manufacturers to comply with 14 CFR §§ 121.346(d)(1),
125.226(d)(1), or 135.156(d)(1). However, for all airplanes of a particular model, the operator must record the individual airplane serial number and U.S. registration number in the correlation documentation for all airplanes on its operations specifications that have identical DFDR systems.
c. How does the operator show compliance? By the last permissible reporting date (October 20, 2011), all operators must have updated correlation documentation stating which of the listed parameters in 14 CFR § 121.346(c) is filtered or not filtered by definition. This must be done for each aircraft listed in the operator’s operations specifications. There are three cases in which an operator would show compliance:
(1) At the report date, no later than October 20, 2011, the operator updates its correlation documentation to show its DFDR system does not record any filtered data for the parameters listed in 14 CFR § 121.346(c). For all airplanes of a particular model, the operator must record the individual airplane serial number and U.S. registration number in the correlation documentation for all airplanes on its operations specifications that have identical DFDR systems.
(2) An operator identifies a Group 2 parameter as being filtered in its correlation documentation and opts to reconstruct the original sensor signal values. The operator must submit the procedures and test and analysis results to reconstruct the filtered data as early as possible, no later than April 22, 2013. The data package must be the updated correlation documentation with at least the following information:
(a) Operating certificate holder name, aircraft type, and DFDR system description, A5-4
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(b) Name, number, and accuracy of the parameter as defined by the applicable operating rule,
(c) Actual measured data from the original source signal exercised in static and dynamic conditions,
(d) Raw DFDR data of the filtered parameter exercised in static and dynamic conditions,
(e) EU conversion algorithm,
(f) Filtered data reconstruction algorithm, and
(g) Analysis of the reconstruction algorithm applied to the raw DFDR data.
(3) An operator identifies a Group 2 parameter as being filtered and opts to redesign the DFDR system to record original sensor signal data. This case is handled through the STC process.
5. Flowchart. Figure 5-1 is a flowchart of the filtered flight data final rule. This flowchart breaks down the regulatory requirements in 14 CFR § 121.346. Figure 5-1 can be applied to the similar requirements in 14 CFR §§ 125.228 and 135.156.
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Appendix 5 FIGURE 5-1. FILTERED FLIGHT DATA FINAL RULE COMPLIANCE FLOWCHART.
START Are any NO parameters in §121.346(c) (Group 2) filtered ?
END _YES Update correlation Submit STC data to documentation. See ACO for approval. See paragraph 4.c(1) paragraph 4.c(3) Do those Redesign DFDRS to filtered parameters Update correlation record unfiltered data NO YES meet the accuracy documentation. See no later than April 21, 2014. requirement under part 121 Appendix M? paragraph 4.c(1) NO END Can you reconstruct NO the original sensor signal value from the recorded data to meet the parameter accuracy requirement?
Maintain reconstruction procedures and test and analyses results with YES correlation documentation. See Submit reconstruction paragraph 4.c(2) procedures to FAA CHDO.
See paragraph 4.c(2) Are the reconstruction NO procedures and test and YES analysis results approved by the FAA valid and repeatable?
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Appendix 6 APPENDIX 6. DEFINITIONS
1. Applicant. A person seeking FAA approval for a DFDR installation. The approval may be a TC, amended TC, or STC. The approval may apply to a single aircraft or to multiple aircraft of a single type design.
2. Correlation. Describes the relationship between two variables. In the case of the DFDRS, the first variable is the measured or sampled data and the second is the EU converted data in the DFDR.
3. Correlation coefficient. A number that describes the degree of relation between the data being measured or sampled and the data derived from the recorder. The correlation coefficient used here is the Pearson product-moment correlation coefficient, however the coefficient of determination R2 or the sum of least squares methods are acceptable. Its value may vary from minus one to plus one. A value of positive one (1.0) indicates a perfect direct correlation. A value of zero indicates there is no correlation, or any predictive capability between the derived data (using the equation) and the raw data is purely coincidental. A value of negative one (-1.0) indicates a perfect inverse relationship between the derived value and the raw data. The absolute value of the correlation coefficient must be equal to or greater than 0.99 over the entire operating range of each mandatory parameter to accurately establish the conversion of recorded values to EU. See appendix 1 for one method, but not the only method, to determine the correlation coefficient.
4. Correlation data. The documentation required by 14 CFR § 121.344(j)(3), 121.344a(d)(3),
125.226(j)(3), and 135.152(f)(2)(iii). This documentation must show how each parameter was correlated and be maintained by the operating certificate holder.
5. Date of manufacture. Different dates of manufacture may be triggered by the varying regulatory requirements applicable to an individual aircraft. When two or more regulations apply, each with their own date of manufacture, the FAA recommends using the earliest date required as compliance for all of the regulations under which a date of manufacture is specified.
6. Dedicated sources. Any digital system interface, analog discrete interface, or analog sensor interface installed solely to produce an input signal to the DFDRS. For example, if it is necessary to install a horizontally mounted accelerometer to sense lateral acceleration, then this accelerometer is considered a dedicated sensor. Conversely, the vertical accelerometer may exist on the aircraft for another reason (vertical flight control, for instance). If the DFDR takes vertical acceleration data from such an existing accelerometer, then the vertical accelerometer is not part of the DFDRS. However, the accelerometer must meet the accuracy requirements listed in the appropriate regulatory appendix.
7. Digital flight data acquisition unit (DFDAU). An electronic device that collects, samples, reformats, and digitizes analog and digital signals representing aircraft flight data. See ARINC Characteristic 717. The equivalent of this function may be incorporated in other hardware that may not meet the classical definition of an ARINC 717 DFDAU.
8. Digital flight data acquisition function (DFDAF). Software performing the function of a DFDAU in a larger avionics system.
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Appendix 6
9. DFDR. A recording device using a digital method to record and store data onto a storage medium and to retrieve that data from the medium. A DFDR may be the storage device in a recording system that includes a DFDAF, DFDAU, or an FDAU. Or, it may be a stand-alone device using an internal data collection system to convert aircraft analog and discrete signals to digital form.
10. Digital flight data recorder system (DFDRS). The software, equipment, sensors, wiring, equipment racks, and other items installed in the aircraft to record flight data. It includes the following equipment items: DFDR, dedicated sensors, underwater locating device (ULD), and a DFDAF, DFDAU, or FDAU.
11. Dynamic condition. The parameter is experiencing change at the maximum rate attainable, including the maximum rate of reversal.
12. Flight data acquisition unit (FDAU). The predecessor to the DFDAU, defined by ARINC 573. It is primarily designed to accept analog and analog discrete input data, and in some cases, it will accept digital data on predefined inputs.
13. Flight data recorder (FDR). A recording device directly receiving analog signals representing various aircraft functions (e.g., vertical acceleration, heading, altitude, or airspeed) and recording those signals in digital or analog format. Older FDRs recorded the signals by scratch with a stylus on a moving oscillographic medium, typically a foil formed from steel or steel alloy. These older analog FDR installations typically conformed to ARINC Characteristic 542. The FAA now requires that DFDRs be used in the U.S. commercial fleet.
14. Functional check. A check to determine if one or more functions of a DFDRS perform within specified limits. The following identifies and defines three types of DFDRS functional checks.
a. First of type:
(1) The applicant must perform the first of type installation testing for an FAA approval (TC, amended TC, or STC). This check determines if the range, accuracy, sampling rate, and resolution of each parameter is within specified limits. During the first of type functional check, it may not be feasible to stimulate some sensors to their specified limits. In such instances it is acceptable to simulate the sensor output using suitable test equipment. This check collects correlation data in support of certification. See appendix 2 for procedures when a DFDR data correlation document does not exist for an aircraft.
(2) For data received by the recording system in a digital means, credit may be given to the source system in determining the range and resolution of the parameter. Range and resolution are functions, not necessarily of the recording system, but of the source system.
However, the range and resolution of the source system must meet the minimum requirements of the applicable appendix in 14 CFR. If the range and resolution satisfy the requirements in the applicable appendix in 14 CFR, there is no need to repeat these checks for the purpose of meeting recording system requirements.
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(3) For dedicated parameters that are analog and analog discrete in nature, all of these requirements should be checked.
b. Operational: The operational check is a task to determine an item is fulfilling its intended purpose. An operational check is a failure-finding task and does not determine if the item is performing within specified limits. When applied to a DFDR, the operational check determines the DFDR is active and recording each parameter value within the normal operating range of the sensor. The operational check must also verify each electrical interface to the DFDRS. This may take place off the airplane.
c. System: A system functional check confirms interfaces to the recording system are present and functioning. This test confirms the presence of the electrical interfaces to the recording system and the function of dedicated sources. The operator must include a system functional check in the maintenance program. For dedicated sources, you may simulate sensor or transducer outputs to check the range, accuracy, sampling rate, and resolution of the recorded data. However, the instructions for continued airworthiness (ICA) and the operator’s maintenance program must prescribe a periodic system functional check of each of these transducers or sensors for range and accuracy.
15. Installed and connected to the recording system. This refers to the requirement to record parameters in addition to those specifically identified in the regulation (i.e., 22, 34, or 57 parameters, based on the date the aircraft was manufactured; see appendix 3). The DFDRS must record the parameters required by the aircraft’s existing DFDRS on July 16, 1996 if sufficient capacity is available in the upgraded DFDR. However, an operator is not required to upgrade the capacity of an installed recording system beyond that needed to record the mandated parameters.
In other words, a previously installed DFDR must continue to record parameters it was recording effective as of July 16, 1996, plus additional parameters if they are already connected and available to the system and if capacity exists in the system to record the parameters. Thus, if a retrofitted DFDRS can accommodate additional parameters, the retrofitted DFDR must continue to record any parameters not specifically mandated, but may be accommodated by the upgraded DFDRS. The FAA considers a parameter to be easily accommodated if it is provided by an installed system and it is already connected to the data bus. (See Sufficient Capacity definition below.)
16. Readily retrievable. This term means that the actual sensor value of the mandatory parameter can be retrieved from the storage medium by qualified personnel in 8 hours using:
a. Existing, easily understood instructions and commonly available tools and techniques;
and
b. Step-by-step procedures, including all conversion algorithms, necessary to derive and validate the values.
Note: These procedures must be a permanent part of the aircraft-specific DFDRS documentation package. Portions of the documentation package pertaining to the format and conversion algorithms of the recorded data may be recorded within the crash-protected memory of the DFDR.
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17. Reasonableness. An off-airplane review of recorded data to assess the overall health of the recording system parameter. The review requires technical judgment to assess a parameter’s health functions off the airplane. Typically, the data is downloaded from the airplane and reviewed in a ground station tool away from the airplane, using graphical and tabular means.
The reasonableness check may identify gross parameter anomalies, such as static parameters, missing parameters, random movement in parameters, parameters not in agreement with related parameters in a given operational range or mode, etc. Technical judgment is required during the review so that the reviewer does not confuse acceptable airplane operational differences with parameter recording anomalies (i.e., the reasonability check is for parameter health and not piloting technique).
18. Single source. This term applies to certain split flight control parameters. It means that if it is necessary to conserve capacity in order to record the required parameters, the DFDR must record the position of only one of the two flight control positions.
a. For example, the DFDR may record the position of the aileron bellcrank instead of each aileron surface position. However, any recording from a single source must be made so the position of the flight control input can be differentiated from the position of the flight control surface.
b. In the example given, the installation instructions must tell the installer to place the aileron surface position sensor on one or the other bellcrank lobes to which one of the aileron surface actuator arms is attached—not the lobe to which the control yoke is attached.
19. Split flight control parameter. This applies to flight control and flight control surface parameters when the flight control system design allows the flightcrew to disconnect the captain’s controls from the first officer’s controls. This flight control system design is also known as breakaway capability.
a. The DFDRS must record multiple flight control positions, as well as multiple flight control surface positions.
b. For example, an aircraft flight control system design may allow the flightcrew to disconnect the captain lateral (aileron) control from the first officer lateral (aileron) control. The disconnection would leave the left aileron connected to the captain lateral (aileron) control and the right aileron connected to the first officer lateral (aileron) control. This would leave the captain capable of operating only the left aileron, and the first officer capable of operating the right only.
c. The captain and first officer control inputs (parameter 13) would be a split parameter necessitating each pilot’s lateral control position be recorded. The DFDRS must record both the left and the right lateral control surface (aileron) position (parameter 16) as well.
20. Sufficient capacity. This addresses the existing capacity of the installed DFDRS (either before retrofit or in new production) with regard to the addition of available parameters to be connected to the recording system. These parameters are in addition to the 22, 34, 57, or 88 parameter requirements, based on the aircraft date of manufacture (see appendix 3). Adding these parameters should not force the installation of a higher capacity acquisition unit (FDAU or A6-4
Appendix 6 DFDAU) or DFDR to accommodate these parameters. For example, if the existing DFDRS functions at a 64 word-per-second rate, the rule does not require the applicant to upgrade the system to function at a 128 word-per-second rate to accommodate these parameters, even if it means disconnecting previously recorded parameters that are not required to be recorded. (See, Installed and Connected to the Recording System, definition above.)
21. When an information source is installed. When this term appears in the parameter listing in the 14 CFR section or appendix, the parameter is mandatory only if the aircraft is fitted with a system that provides that capability. For example, it is not necessary to install an ice detection system to comply with parameter 61, but, if an ice detection system is already installed on the aircraft, the DFDRS must record its operation.
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