Advisory

Circular

U.S. Department

of Transportation

Federal Aviation

Administration

Subject: AIRWORTHINESS AND OPERATIONAL Date: 10/05/99 AC No: 20-141

APPROVAL OF DIGITAL FLIGHT DATA Initiated by: AIR-130 Change:

RECORDER SYSTEMS

1. PURPOSE. This advisory circular (AC) provides guidance on design, installation, and

continued airworthiness of Digital Flight Data Recorder Systems (DFDRS). This AC is not

mandatory and is not a regulation. It outlines one method of compliance with Title 14 of the

Code of Federal Regulations. Instead of following this method, the applicant may elect to

follow an alternate method, provided the alternate method is acceptable to the FAA

Administrator for compliance with 14 CFR. Because the method of compliance presented in

this AC is not mandatory, the term “must” used herein applies only to an applicant who chooses

to follow this particular method without deviation.

2. RELATED SECTIONS OF 14 CFR. Sections of 14 CFR parts 23, 25, 27, 29, 91, 121,

125, 129, and 135 that prescribe design substantiation and operational approval requirements

that are directly applicable to the DFDRS are listed here. See appendix 3 of this AC for typical

additional design substantiation requirements of these parts.

 a. Section 23.1459, Flight Recorders.

 b. Section 25.1459, Flight Recorders.

 c. Section 27.1459, Flight Recorders.

 d. Section 29.1459, Flight Recorders.

 e. Section 91.609, Flight Recorders and Cockpit Voice Recorders.

 f. Section 121.343, Flight Recorders.

 g. Section 121.344, Digital Flight Data Recorders for Transport Category Airplanes.

 h. Section 121.344a, Digital Flight Data Recorders for 10-19 Seat Airplanes.
AC 20-141 10/05/99

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 i. Section 125.225, Flight Recorders.

 j. Section 125.226, Digital Flight Data Recorders.

 k. Section 129.20, Digital Flight Data Recorders.

 l. Section 135.152, Flight Recorders.

3. DEFINITIONS. The following definitions apply when these terms appear in the rule or this

advisory circular:

 a. Applicant. The applicant is an individual or organization that is seeking FAA approval for

a digital flight data recorder (DFDR) installation. The approval may be a Type Certificate,

(TC), Amended Type Certificate (ATC), or Supplemental Type Certificate (STC). The

approval may apply to a single aircraft or to multiple aircraft of a single type design.

 b. Correlation. A correlation describes the relationship between two variables. In this case

the two variables are the raw data stored in the DFDR and the engineering units or discretes

that this raw data represents. The applicant must establish the correlation between the raw data

and the engineering units for all mandatory parameters. Reference Section 121.344 (j). The

correlation required in the type certification regulations (Section 25.1459(c) for example) does

not meet the requirement of Section 121.344(j). The applicant must use the correlation

coefficient to describe this relationship. See appendix 1 for a method to determine the

correlation coefficient.

 c. Correlation Coefficient. The correlation coefficient is a number that describes the degree

of relation between the raw data and the derived data. The correlation coefficient used here is

the Pearson product-moment correlation coefficient. Its value may vary from minus one to plus

one. A value of plus one indicates a perfect positive correlation. A value of zero indicates that

there is no correlation or that any predictive capability between the derived data (using the

equation) and the raw data is purely coincidental. A value of minus one indicates a perfect

inverse relationship between the derived value and the raw data. The absolute value of the

correlation coefficient must be equal to 0.9 or greater over the entire operating range of each

mandatory parameter in order to accurately establish the conversion of recorded values to

engineering units.

 d. Date Manufactured. The date manufactured is the point in time at which the airplane

inspection acceptance records reflect that the airplane is complete and meets the FAAapproved type design.

 e. Digital Flight Data Acquisition Unit (DFDAU). A digital flight data acquisition unit

(DFDAU) is an electronic device that collects, samples, conditions, and digitizes analog,

discrete, and digital signals representing aircraft functions. It supplies a serial digital bit stream to

the DFDR. A DFDAU differs from a Flight Data Acquisition Unit (FDAU) in that a DFDAU is
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capable of receiving both analog and digital data streams and converting them to the required

DFDR digital data format. (See Aeronautical Radio Incorporated (ARINC) Characteristic

717.)

 f. Digital Flight Data Recorder (DFDR). A digital flight data recorder (DFDR) is a

recording device that utilizes 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 DFDAU or a 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.

 g. Digital Flight Data Recorder System (DFDRS). The digital flight data recorder system

(DFDRS) is the equipment, sensors, wiring, equipment racks, and other items installed in the

aircraft to record flight data. The DFDRS includes the following equipment items: DFDR,

DFDAU or FDAU, and underwater locating device (ULD). The DFDRS also includes any

sensors or transducers installed specifically to record flight data. For example, if it is necessary

to install a horizontally mounted accelerometer to sense lateral acceleration, then this

accelerometer is considered a part of the DFDRS. 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.

 h. Flight Data Acquisition Unit (FDAU). A flight data acquisition unit (FDAU) is an

electronic device that collects, samples, conditions, and digitizes analog signals representing

aircraft functions. The FDAU does not normally have the capability to condition digital signals.

It provides data to the DFDR in a digital bit stream. See the definition for DFDAU. (See

ARINC Characteristic 573.)

 i. Flight Data Recorder (FDR). A flight data recorder (FDR) is a recording device that

directly receives analog signals representing various aircraft functions (e.g., vertical acceleration,

heading, altitude, or airspeed) and records those signals in digital or analog format. Older

FDR's recorded the signals by scratch with a stylus on a moving oscillographic medium that is

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 DFDR’s be used in the

U. S. commercial fleet.

 j. Functional Check. A functional check is a quantitative check to determine if one or more

functions of an item perform within specified limits. When applied to a DFDR parameter, the

functional check determines that the recorded parameter is within the limits (range, accuracy,

sampling rate, and resolution) specified in the operating rule. The applicant must accomplish a

functional check for all mandatory parameters for the “first of type” installation testing. The

applicant must perform the “first of type” installation testing for an FAA approval (TC, ATC, or

STC). 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. The operator must include a different functional check in the
AC 20-141 10/05/99

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maintenance program. This maintenance functional check applies to those parameters that can

neither be read out during the flight data download, nor functionally checked as part of other

aircraft systems. The maintenance functional check may simulate sensor or transducer outputs

to check the range, accuracy, resolution, and sampling rate of the recorded data. However, the

instructions for continued airworthness and the operator's maintenance program must prescribe

a periodic functional check of each of these transducers or sensors for accuracy and range.

 k. Installed and Connected to the Recording System. The term installed and connected to

the recording system refers to the requirement to record additional parameters in addition to

those specifically identified in the regulation (22, 34, 57, or 88 parameters depending upon the

date the aircraft was manufactured). The DFDRS must record the parameters that were

recorded by the airplane’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, an operator may not discontinue recording parameters it was recording as of

July 16, 1996, if they can be easily accommodated. Thus, if a retrofitted DFDRS can

accommodate additional parameters, the operator must continue to record any parameters that

were not specifically mandated, but that 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 databus. (See sufficient capacity.)

 l. Operational Check. An operational check is a task to determine that 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 that 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. A check to determine the reasonableness and quality of the data being

recorded is considered an operational check.

 m. Single Source. The term single source 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. 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 that the position of the

flight control can be differentiated from the position of the flight control surface. In the example

given, the installation instructions must instruct 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.

 n. Split Flight Control Parameter. The term split flight control parameters applies to flight

control and flight control surface parameters when the flight control system design allows the

flight-crew to disconnect the pilot’s controls from the copilot’s controls. This flight control

system design is also known as breakaway capability. The DFDRS must record multiple flight

control positions, as well as multiple flight control surface positions. For example, an aircraft
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Page 5

flight control system design may allow the flightcrew to disconnect the pilot lateral (aileron)

control from the copilot lateral (aileron) control. The disconnect would leave the left aileron

connected to the pilot lateral (aileron) control and the right aileron connected to the copilot

lateral (aileron) control. This would leave the pilot capable of operating the left aileron only, and

the copilot capable of operating the right only. Thus, the pilot and copilot control inputs

(parameter 13) would be a split parameter necessitating that 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.

 o. Sufficient Capacity. The term sufficient capacity 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, depending upon the airplane date of

manufacture. Adding these parameters should not force the installation of a higher capacity

acquisition unit (FDAU or 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 the definition for installed and connected to the

recording system.)

 p. When an Information Source is Installed. When the term when an information source is

installed appears in the parameter listing 1-88 of the appropriate 14 CFR section or appendix,

the parameter is mandatory only if the airplane 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.

4. SCOPE. This advisory circular provides policy for type certification of a digital flight data

recorder system installation. It applies to installations that are intended to comply with the

requirements of the revisions to digital flight data recorder operating rules that became effective

August 18, 1997. The revised operating rules are Sections 121.344, 121.344a, 125.226,

129.20, and 135.152. This AC also provides guidance to the aircraft operator for compliance

with the operating rules after DFDRS installation.

5. BACKGROUND. On July 17, 1997, the Federal Aviation Administration (FAA) revised

certain sections of 14 CFR to require that certain aircraft be equipped to accommodate

additional digital flight data recorder parameters. The purpose of the revision was to provide

additional information to enable the investigative authority -- the National Transportation Safety

Board (NTSB) in the U. S. -- to conduct more thorough investigations of accidents and

incidents. The data recorded would also be available to industry to enable the prediction of

trends that may be useful in determining modifications needed to avoid accidents and incidents.

The revised rules require that certain turbine-engine-powered airplanes and rotorcraft having 10

or more passenger seats be equipped to record specified parameters. Many currently operating
AC 20-141 10/05/99

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aircraft have low capacity Flight Data Recorder Systems installed. A rule requiring immediate

retrofits would have significantly impacted the air transportation industry economically both in

scheduling and equipment installation costs. In some cases the equipment had not yet been

developed. Accordingly, the FAA provided an extended schedule for retrofit of in-service

aircraft. This AC provides guidance to applicants for a Supplemental Type Certificate (STC),

and to individuals who are responsible for obtaining operating approval for these DFDR’s.

Aircraft manufacturers who intend to install DFDR’s in newly-manufactured aircraft may also

use this guidance.

6. COMPLIANCE SCHEDULE, OPERATING CERTIFICATE HOLDERS. A holder of

an air operating certificate may not operate an aircraft on its operations specification in air

transportation unless that airplane complies with the flight data recorder requirements of the

appropriate 14 CFR part (121,125, 129, or 135). Those conducting other operations of

multiengine, turbine-engine-powered airplanes or rotorcraft having 10 or more passenger seats

must comply with the flight data recorder requirements of section 91.609(c). All multiengine,

turbine-engine-powered multiengine airplanes having 10 or more passenger seats that are

operating in air transportation under parts 121, 125, 129, or 135 and were manufactured after

August 19, 2002, must be equipped with a DFDRS that records 88 parameters as listed in the

appropriate CFR appendix. The term "having 10 or more passenger seats" refers to the actual

number of seat provisions available for use (seat rail attach positions) in the aircraft as it is

configured for operation, not the approved seating capacity entered on the Type Certificate

Data Sheet (TCDS). The rule change increased to 25 hours the DFDR recording capability

requirement for helicopters operating under part 135 authority but did not affect other helicopter

requirements. Except for certain excluded aircraft, the rules provide a retrofit schedule for

existing and in-production aircraft. Figure 1 summarizes the schedule of part 121 DFDRS

requirements. For a more detailed description of the requirements and retrofit schedule for

these and other aircraft refer to the applicable rule or to appendix 2 of this AC.
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Figure 1. Compliance Schedule for DFDRS Installations (Section 121.344)

Date of Aircraft Manufacture

October 11,1991

Not FDAU

Equipped

FDAU Equipped

Configuration

As of July 16, 1996

3/4 Engines:

17-p / Appx B

2 Engines:

18-p / Appx B

22-p / Appx M

Digital Data Bus

&

DFDAU Equipped

22-p / Appx M

plus

121.344(c)(2)

34-p / Appx M

plus

121.344(d)(2)

121.344(c)(2)

121.344(d)(2)

121.344(e)(2)

"Commensurate with the capacity of the recording system {(DFDAU or equivalent and the DFDR)[(c)(2)]}, all

additional parameters for which information sources are installed and which are connected to the recording system, must

be recorded within the ranges, accuracies, resolutions, and sampling intervals specified in Appendix M of this part."

Retrofit Required by Next HMC After

August 18, 1999 and by August 20, 2001

August 20, 2000 August 19, 2002

57-p / Appx M

plus

121.344(e)(2)

88-p / Appx M

plus

7. TYPE CERTIFICATION. The applicant must obtain FAA approval to install or to retrofit

a DFDR and components. The applicant may apply for a TC, an ATC, or an STC. The FAA

will not make field approvals. The applicant must demonstrate compliance with the applicable

regulations included in the type certification basis for the aircraft. Appendix 3 lists typical

certification requirements that are applicable depending upon the certification basis of the

aircraft. The type certificate data sheet (TCDS) referenced in the type certificate normally

identifies the applicable regulations. An applicant must demonstrate compliance with the

appropriate certification requirements as instructed by the approving Aircraft Certification Office

(ACO). (See appendix 3.)

 a. DFDRS Descriptive Data. The applicant must include in the system description the make

and the model or part number of the DFDR, FDAU, or DFDAU (or equivalent). Include a

listing of each parameter recorded and identify any transducers or sensors installed specifically

for the purpose of sensing required data. Such identification must include the manufacturer and

part number of the sensor. For those sensors not dedicated exclusively to the DFDRS, identify

and include in the system description the sensor source and the associated digital data bus

source. The description must identify any reliance upon pneumatic inputs directly to the

DFDRS for pitot-static information. Identify those components of the DFDRS that meet TSO

standards including the TSO number and any authorized deviations from the TSO requirements.

Describe any necessary structural alterations associated with the installation. The description

must include a wiring diagram and schematic and must describe all dedicated wires. Identify all

interfaces to other installed equipment and systems.
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 b. Intended Function. The applicant must provide a list of all parameters that the DFDR will

record and their specifications (range, accuracy, sampling rate, sampling interval, and

resolution). The applicant must demonstrate, by tests, that the DFDRS meets these

specifications. These tests are normally performed using simulated inputs to the DFDRS and by

activating transducers and sensors installed as part of the DFDRS. Where the aircraft sensor is

a synchro, and the installation design allows switching of the sensor or the digital bus during

flight, the applicant must demonstrate performance in all switched positions. As part of this test,

the applicant must provide a correlation document (data stream format and correlation

document as described in appendix 1).

NOTE: Before performing ground or flight tests on the DFDRS

installation, the applicant must perform a conformity check. This check

must demonstrate that the DFDRS installation conforms to the design

data that will be cited on the type certificate, amended type certificate, or

supplemental type certificate.

 (1) The applicant must identify any parameters that are filtered before they are recorded.

For these parameters, the applicant must show, by test, that there is no significant difference

between the recorded parameter data under both static and dynamic (parameter undergoing

change at the maximum rate expected when operating the aircraft in accordance with the flight

manual) conditions. For purposes of this test, the term "no significant difference" means that any

differences between the data recorded under static conditions and the data recorded under

dynamic conditions should be less than the correlation coefficient derived using static parameter

values.

 (2) The applicant must also perform a ground cockpit compatibility check to demonstrate

performance of the DFDRS installation. This compatibility demonstration must include:

 (a) A demonstration that the circuit breaker can be identified and reset from a

flightcrew position (if a circuit breaker is provided for crew reset);

 (b) A check that the DFDR "preflight check" indicator or display is visible (or aural

tone is audible) to the flightcrew; and

 (c) A demonstration of any DFDR-related items in the airplane flight manual

(supplement) to verify that aircraft flight manual (AFM) procedures have not been invalidated by

the installation..

 (3) The applicant must perform a test to demonstrate that the DFDRS is not susceptible

to electromagnetic or radio frequency interference (EMI/RFI) and that it does not generate such

interference in essential and flight-critical systems. The applicant must demonstrate EMI/RFI

compatibility with engines and all essential systems operating for a new DFDRS installation.
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NOTE: The STC process does not provide for findings of compliance with

operating rules such as section 121.344. An FAA Flight Standards inspector

must make such findings of compliance for individual aircraft upon

completion of the aircraft installation. However, an applicant for type

certificate approval (TC, ATC, or STC) may facilitate the operator’s later

demonstration of compliance to the operating rule by referencing the

appropriate appendix and parameter numbers of parts 121, 125, or 135 for

the specifications met when demonstrating that the DFDRS performs its

intended function. The FAA inspector may use the test report to support a

finding of compliance with the operating rule. The applicant should

substantiate any discrepancies between the parameter specifications in the

appropriate appendix of the operating rule and those demonstrated by test.

Such substantiation is needed for the ACO to find “novel, unique design, or

operational characteristic.”(See Section 25.1459(e) or equivalent.) The

operator may later use this substantiation to support a petition for

exemption from the operating rule. For example, the applicant may need to

substantiate a unique design characteristic to change the way the DFDR

records a required parameter if such recording would compromise a critical

function of the aircraft. In this case, the operator that installs the FAAapproved system must then request an exemption from the parameterrecording requirement. (See 14 CFR section 11.25 for procedures to petition

for an exemption.)

 (4) The applicant must demonstrate that the DFDRS performs as intended, that it does

not cause electromagnetic interference (EMI) in essential or flight critical systems, and that

electromagnetic fields from other operating electrical and electronic systems and components do

not cause noise or data dropouts in the DFDR recorded data. If the applicant cannot

demonstrate these capabilities using ground tests, a flight test must be performed. After the

flight test, the applicant must conduct a reasonableness and quality check of the DFDR data

from the flight test. The purpose of this check is to demonstrate that each parameter is being

recorded properly and that any data dropouts or noise do not interfere with the ability to

interpret the data. Appendix 4 presents a typical flight test sequence and the manually recorded

data needed to conduct the reasonableness and quality check. During the flight test, the

applicant must demonstrate that the DFDRS is not susceptible to electromagnetic or radio

frequency interference (EMI/RFI) and that the DFDRS does not generate such interference in

essential or flight-critical systems.

NOTE: Using the flight test data, the applicant must confirm that the

DFDR begins to operate no later than the time that the aircraft begins its

takeoff roll and continues to operate until after the aircraft has completed

its landing roll. For rotorcraft, the DFDR must operate from the instant the

rotorcraft begins its liftoff until it has landed.
AC 20-141 10/05/99

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 c. Equipment and Sensors. The applicant must present evidence that the equipment and

sensors that are to be installed as part of the retrofit are FAA approved or obtain FAA

approval for them. A DFDR or DFDAU that has been manufactured under TSO C-124 or C124a authorization is FAA approved. Likewise, a ULD that has been manufactured under

TSO C-121 authorization is FAA approved. DFDRS equipment installed in turbine-enginepowered airplanes having 10 or more passenger seats and manufactured after August 18, 2000,

must conform to TSO C124 or TSO C124a. Acceptable guidelines for documentation of

DFDR data content and format are also available in the Flight Recorder Configuration Standard

(FRCS), Document TP13140E. The FRCS is available from Transport Canada Safety and

Security at:

Transportation Development Centre

800 Rene Levesque Blvd. West, Suite 800

Montreal, Quebec, Canada H3B 1X9

Telephone, (514) 283-0000, FAX (514) 283-7158

e-mail: tdccdt@tc.gc.ca

NOTE: The DFDR installed in aircraft operated under 14 CFR parts 121,

125, 129, and 135 must be capable of recording flight data for 24 hours or

more. Therefore, in order to avoid installation of an 8-hour recorder in

these aircraft, any DFDR that is capable of retaining no more than 8 hours

of data must bear a placard stating: “Approved for use in aircraft

operating under 14 CFR part 91 only.” The placard must be printed in 5/16

inch bold block letters. The placard must be affixed to a surface of the

DFDR so that it is easily visible when the DFDR is installed.

 (1) Altitude and Airspeed Sensors. When an air data computer is installed, the pressure

altitude and indicated or calibrated airspeed must be recorded from the air data computer.

When two air data computers are installed, one supplying the pilot instruments and the other

supplying the co-pilot instruments, the pressure altitude and indicted or calibrated airspeed must

be recorded from both air data computers. However, the air data computer outputs may be

sampled alternately once every 2 seconds to produce the sampling interval of 1 second. When

there is no air data computer, the pressure altitude and indicated or calibrated airspeed may be

derived from either of the pilot's instrument systems or it may be derived from a separate pitotstatic system. Where the data is derived from the pilots' instruments, the pilots' instruments must

not be impaired. Where the data is derived from a separate pitot-static system, the accuracy of

the data must be equal to that of the pilots' instruments over the full flight envelope of the

aircraft.

 (2) Control Position and Forces (non-fly-by wire). Control positions and control forces

must be measured at the control columns, control wheels, and rudder pedals, if practical.

Where the applicant shows that this is impractical, the positions and forces may be measured on

the first lever arm or on the first bell crank in the control linkage from the control. Should the

applicant determine that installation of the sensor on this first control arm or bell crank is
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impractical, the applicant should conduct an analysis to show that the likelihood of mechanical

interference that could invalidate the recorded position and force values is improbable (1x10-6).

 (3) Thrust Command and Thrust Target. Thrust command and thrust target are typically

available on airplanes equipped with a Full Authority Digital Electronic Control (FADEC).

Thrust command is the thrust required by the FADEC for some predefined schedule. Thrust

target is the thrust to be achieved at the end of the thrust command schedule. Once the thrust

target is achieved, the thrust command and the thrust target will be the same.

 (4) Computer Failure Discrete. This parameter is a discrete and should be activated upon

failure of any computer that could directly affect the primary and secondary flight controls or the

engine controls (primarily the throttles). Some examples of computers that should be monitored

for failure are those that are a part of the Flight Management System, the auto-throttle system,

and the autopilot. Furthermore, if a computer drives any of the above computers, and there is

no discrete transmitted to that computer from the device, that device's computer should also be

monitored.

 (5) Multiple Control Surfaces (flap sections, aileron/spoiler speed brake panels) and

Combinations for Lateral Control. Ailerons on each wing must be monitored separately.

Multiple aileron surfaces that are mounted on the same wing must be monitored separately

unless the designer shows that it is improbable that all surfaces would not deploy as intended.

All secondary control surfaces (e.g., flaps, speed brakes, and spoilers) that normally activate

together but can activate independently of each other should also be monitored separately

unless the designer shows that it is improbable that a surface would not deploy as intended.

 (6) Multiple Thrust Reverser Buckets. Each individual thrust reverser bucket must be

monitored unless the designer shows that it is improbable that an individual bucket would deploy

without intentional deployment of all buckets at once.

 (7) Hydraulic Pressure. Hydraulic pressure low, each system (parameter 33) and

hydraulic pressure each system (parameter 77) are both required parameters. Although

hydraulic pressure low is defined as a discrete the comment in the range column of appendix M

indicates that it may also be recorded as an analog signal representing the actual value of the

hydraulic pressure. Thus, either the hydraulic pressure LO discrete or the actual analog

hydraulic pressure may be recorded for all DFDRS installations except those on airplanes

manufactured after August 19, 2002. For airplanes manufactured after August 19, 2002, both

parameter 33 and parameter 77 are required. Thus, both the hydraulic pressure low discrete

(parameter 33) and hydraulic pressure (parameter 77) must be recorded for these airplanes.

 (8) Safety Evaluation of Sensors Installed in Flight Control Systems. Some flight control

surface and flight control input sensors consist of rotary synchros that are tied into the flight

control system using mechanical arms and links. The ends of the links (rod ends) and the

synchros have bearings that may be subject to seizure due to loss of lubrication. Such seizures

may jam flight controls resulting in a catastrophic failure condition. The applicant must conduct
AC 20-141 10/05/99

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a safety analysis to evaluate the reliability and fail-safe aspects of sensor hardware installed in

flight control paths. The analysis should demonstrate that no catastrophic failure would occur

during the life of the aircraft. As a result of this study, the applicant may find it necessary to

prescribe periodic inspection or replacement of the sensor(s) in the instructions for continued

airworthiness.

 d. Combination CVR/DFDR Units. Under longstanding FAA policy an applicant may

install a combination cockpit voice recorder (CVR) and DFDR unit instead of the DFDR.

However, the combination CVR/DFDR may not serve as both the required DFDR and the

required CVR. That is, the applicant may use a combination CVR/DFDR for either the

required DFDR or CVR, or the applicant may install two combination CVR/DFDR units in the

aircraft, one for each required system.

 e. Software. For those DFDR’s having DO-178B Level E or DO-178A Level 3 software

installed, and those DFDR’s for which no software approval exists, the applicant must:

 (1) Obtain certification from the equipment manufacturer that the source code has been

archived.

 (2) Obtain certification from the equipment manufacturer that the executable object code

can be regenerated from the archived source code.

 (3) Demonstrate that the software to be loaded during DFDRS installation or during

DFDRS maintenance can be successfully loaded through the use of released procedures. These

procedures should be included as part of the installation instructions or the instructions for

continued airworthiness, as appropriate.

 f. Weight and Balance. The applicant must determine the effect of each item of equipment

that has been removed or installed on the aircraft weight and balance. The applicant must

present a report showing the net change in weight and moment (or moment arm). The report

must show how the applicant determined this net change. The applicant must also submit a flight

manual supplement to the ACO for approval, if the installation results in changes to the weight

and balance procedures in the airplane flight manual.

 g. Electrical Loads Analysis. The applicant must determine the effects of each installed and

removed item of electrical equipment on the electrical load to the aircraft power distribution

system. The applicant must present a report showing the net change in the electrical load on

each affected bus and how the applicant computed this net change. The applicant must also

identify any necessary changes in circuit protective devices. The net change to the load carrying

capability of the essential bus must not result in interruption or otherwise adversely affect power

supplied to items on that bus.

 h. Electrical Power Source. The DFDR must receive its operating electrical power from the

bus that allows maximum reliability for the DFDRS. The applicant may not add the DFDR to
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any bus if the addition would jeopardize essential or emergency loads. The applicant must

connect the DFDRS and the cockpit voice recorder (CVR) to power busses that are separate

and supplied by independent power sources. If the DFDRS cannot be added to the emergency

or essential bus, the applicant should consider providing two separate and independent sources

of electrical power for each DFDR and its associated FDAU or DFDAU. In addition, the

applicant should consider providing that each DFDR and its associated FDAU or DFDAU

automatically switch between the two power sources to maintain flight data recording in the

event of a bus failure. Such provision of two separate and independent power sources would

ensure that available data essential to accident investigation is recorded throughout the entire

accident sequence.

NOTE: If the applicant is upgrading an existing approved DFDRS

installation in order to comply with the new operating requirements of

Amendment 121-266,

125-30, or 135-69, and the upgrade would not otherwise require revised

power circuitry, the applicant need not revise existing power circuitry to

provide automatic switching capability.

 i. Circuit Protective Devices. If a circuit protective device for the DFDR is provided in the

cockpit, it must be resettable and located so that it can be readily reset in flight. Advisory

Circular 25.1357-1 describes an acceptable means of making circuit protective devices

accessible so that they can be reset in flight.

 j. Preflight Monitoring Means. The preflight monitoring means is an aural or visual indicator

in the cockpit that is activated when any one of a combination of system status monitors and

built-in test capabilities fail. For example, an indicator light may monitor the following functions,

depending upon availability of built-in test capability:

 (1) Loss of system electrical power;

 (2) Failure of the data acquisition and processing equipment; and

 (3) Failure of the recording medium and/or drive mechanism.

 k. Aircraft Flight Manual Review. The applicant must review the aircraft flight manual

(AFM) and supplements to determine that they are compatible with the DFDRS installation.

The applicant must provide an approved AFM supplement to eliminate any incompatibilities.

 l. Instructions for Continued Airworthiness. The applicant must provide instructions for

continued airworthiness as part of the substantiating data. These instructions must include as a

minimum:

 (1) A document containing the data stream format and correlation data outlined in

appendix 1.
AC 20-141 10/05/99

Page 14

 (2) An identification of the transducers installed exclusively for the DFDRS (that is, those

that supply signals only to the DFDRS and not to other aircraft systems). The signals from these

transducers cannot be verified during checks of other aircraft systems and equipment; therefore,

they must be checked using specifically-devised procedures. For example: vertical, longitudinal,

and if applicable, lateral acceleration.

 (3) A document providing procedures for a ground check. The ground check must

confirm the recorded value of each parameter that is generated by a transducer or other signal

source exclusive to the DFDRS. The document must provide sufficient information to verify the

accuracy of the recorded data (as required by part 121, appendix B or M; part 125, appendix

E; or part 135, appendix B, C, or F).

 (4) A document providing procedures for performing an operational and functional

ground check. The document must provide sufficient information such that a technician can

assess the reasonableness of the recorded values for each mandatory parameter and the quality

of the recording. The document must enable the technician to conduct an operational

(reasonableness and quality) check by periodic readout of the recorded parameters from any

flight. The readout must be in engineering units and discrete states. It must also provide

procedures (and recommended check intervals) to functionally check parameters, such as

warning discretes, that are not typically activated and recorded during the aircraft operation

segments being used for the operational check. The document may reference procedures for

such checks furnished in the aircraft manufacturer's instructions for continued airworthiness. See

appendix 5 for typical reasonableness and quality check instructions.

NOTE: The term reasonableness refers to the read-out of recorded

parameter values. The procedures determine reasonableness of parameters

in a typical segment of flight by comparing these readouts to expected

values, directions of change, and rates of change. The flight segments are:

takeoff roll, takeoff, climb, cruise, approach, landing, and landing roll-out. .

The reasonableness check should be accomplished in those segments that

exercise the majority of the parameters. These segments are takeoff, climb,

approach, and landing. If parameters are recorded during taxi, they should

be used as well. An example reasonableness check might be to examine the

altitude value during taxi. An altitude reading during taxi or takeoff roll,

that deviates significantly from field elevation should signal the analyst to

check the altimeter setting to determine if it was correct or to check the

static system and altimeter. An example of poor data quality is 15 data

“drop-outs” in a 45-second period of flight for parameter (13) pitch control.

This indicates poor data quality since the analyst would find it difficult to

correlate pilot control inputs to aircraft attitude and position. The quality

assessment must determine that there are no instances of noise or data

dropouts that interfere with the analysts' ability to correlate interdependent

parameters.
10/05/99 AC 20-141

Page 15

 (5) A document providing repair and replacement instructions for DFDRS equipment and

sensors. This document must include instructions for conducting a functional check of the

affected parameter(s). The functional check must include instructions for verifying that the data

stream format and correlation documentation is correct.

 (6) If the retrofit includes a change to the underwater locating device (ULD), the

applicant must provide instructions for periodically replacing the ULD battery and conducting an

operational check of the ULD. The replacement period must be consistent with the battery

manufacturer’s life limit. The applicant must include instructions for how to access the ULD.

Advisory Circular 21-10A, Flight Recorder and Cockpit Voice Recorder Underwater Locating

Devices, provides guidance for ULD installations.

NOTE: If the ULD battery is not accessible, the instructions must be for

replacement of the ULD itself.

 (7) The applicant may design the installation to accommodate DFDRS equipment of

different part numbers or of different models and part numbers. For example, the DFDRS

equipment manufacturer may assign one part number to equipment that meets the requirements

of TSO C124 and another part number to equipment that meets TSO C124a. The two

different part-numbered DFDR's are identical except that the latter has been shown to withstand

the more severe fire resistance test requirements of TSO C124a. Since the FAA accepts both

DFDR's, the applicant may wish to allow installers to select either DFDR for installation. In this

case, the applicant must provide a list identifying the interchangeable items of equipment by

make, model, and part number.

8. AFTER INSTALLATION. Before a newly manufactured aircraft is put into service or a

retrofitted aircraft is returned to service, the operator must demonstrate conformity to the type

design or supplemental type design data. The operator must demonstrate this conformity to an

FAA airworthiness inspector. The inspector must determine that the operator has demonstrated

the following functions, or that the FAA has exempted the operator from the operational

requirement:

 a. Parameter Operational Check. The operator must perform an operational and functional

check to determine that each required parameter is being recorded, that the recorded value is

reasonable, and that data quality is sufficient to interpret the data. This operational and

functional check is also referred to as a reasonableness and quality check. Any parameter that

is generated by a sensor or transducer installed as part of the DFDRS or exclusively used by the

DFDRS must be functionally checked at the time that the operational check is accomplished.

See paragraph 7.l.(3). The operator must retain the downloaded data (raw data in electronic

format that can be deciphered using the Data Stream Format contained in the correlation

document is acceptable) used in this check as a permanent part of the aircraft records. The

operator must note in its maintenance program how to access the downloaded data used in this

check. See paragraph 7.l. (4) for a description of the operational and functional check.
AC 20-141 10/05/99

Page 16

 b. Correlation Document (Data Stream Format and Correlation Document). The operator

may use an approved correlation document supplied by the FAA approval holder or develop a

separate correlation document. The document describes the data stream format and includes

correlation data for each mandatory parameter. Where the operator has obtained approval to

deviate from the approved installation data, the operator must verify that the approval holdersupplied correlation data remains valid for those mandatory parameters affected by the

deviation. The operator must generate and maintain individual aircraft correlation data where

significant deviations from the FAA-approved correlation data exist. The deviation is significant

if the applicant cannot demonstrate that the difference between the derived data for the “as

installed DFDRS” and the derived data for the “FAA approved DFDRS” is within the accuracy

specification of the appropriate appendix. (See appendix 1.)

 c. Parameter Specification Demonstration. The operator must verify that all parameters

required by the operating rule are being recorded to the specifications (time correlation, range,

resolution, accuracy, and sampling rate) provided in the appropriate appendix. For multiple

DFDRS installations, as described in section 121.344(j), the operator may demonstrate

compliance by comparing the FAA approval holder’s approved parameter list and correlation

document (data stream format and correlation document as described in appendix 1) to the

appropriate appendix of the operating rule.

 d. Data Retention Provisions. The operator must demonstrate that when removing a DFDR

from an aircraft, all recorded flight data is retained until the operator has operated the aircraft for

an additional 25 hours or more. The term “operate the aircraft for an additional 25 hours or

more” refers to the total time of all flight since the DFDR was removed, including the time from

start of the use of the checklist (before starting engines for the purpose of flight), to completion

of the final checklist at the termination of flight.

9. MAINTENANCE PROGRAM. Each operator must change its maintenance program, as

necessary, to include administrative procedures for scheduling, accomplishing, and recording

maintenance and inspection actions to accommodate the required changes to the DFDR system.

The maintenance program must identify inspection items, establish time-in-service intervals for

maintenance and inspections, and provide the details of the proposed methods and procedures.

An operator may include the maintenance and inspection program for the underwater locator

device (ULD) in the DFDR system program or develop it separately. The maintenance

program must include the following items:

 a. Describe the DFDRS. The system description must include the make and model, or part

number of the DFDR and each DFDAU or FDAU. It must include a listing of each parameter

recorded, and must identify any transducers installed specifically for the purpose of sensing

DFDR required data. Such identification must include the manufacturer and part number of

each sensor. The description must include a wiring diagram and schematic, and describe all

dedicated wires and digital data busses. The system description must identify all interfaces to

other installed equipment and systems.
10/05/99 AC 20-141

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 b. Describe the scheduled maintenance tasks for each component of the DFDRS. This

description must include an operational and functional ground check of all mandatory

parameters recorded by the DFDR. The operational check procedure must determine the

reasonableness of mandatory parameters recorded by the DFDR. It must also determine that

the data quality pertaining to noise and data dropouts allows one to correlate related

parameters. The operational check must be accompanied by a functional check to verify the

performance of any mandatory parameters not verified from the flight data used during

operational check or by functional tests of other aircraft systems. The operational check

description must provide sufficient information to assess the reasonableness and quality of the

recorded values. The operator must use a periodic readout or electronic data extraction of the

flight recorder to accomplish this requirement. The operator must include a separate operational

check for mandatory parameters, such as warning discretes, (If the DFDAU posts in the

recorded data that the bus is operational, an existing operational test that shows that the

DFDAU is receiving data is adequate for this purpose) not typically activated and recorded

during the aircraft operation segments being used for the operational check. The ground

operational check must also include procedures to determine the reasonableness of any

recorded non-mandatory parameters. Appendix 5 describes typical reasonableness and quality

check requirements for a 34-parameter installation.

NOTE: Some test units are available that record or display the data going

into the DFDR rather than downloading the data actually stored in the

DFDR. Such units are not acceptable for use in conducting the

reasonableness and quality check as it does not allow one to assess the

quality of recorded data.

 c. Provide for the retention of DFDR correlation document data stream format and

correlation document as described in appendix 1 applicable to each individual aircraft. Provide

for retention of additional documents needed to enable accurate conversion of recorded digital

values to their corresponding engineering units or discrete states. These documents must also be

readily available so that they can be delivered to the FAA or the National Transportation Safety

Board (NTSB) after an accident or a reportable occurrence. The data stream format and

correlation document must provide the information described in appendix 1 of this AC.

 d. Provide for updating the correlation and data conversion documentation for each

DFDRS installation. These procedures must also provide for an update, upon modification of a

system that provides parameter input to the DFDR system.

 e. Establish a schedule for accomplishing an operational and functional ground check at

intervals not to exceed 12 calendar months. An operator may adjust this 12-month interval

based upon findings made under the “performance analysis function” of its continuing analysis

and surveillance program. The operator must demonstrate to the FAA that these findings are

satisfactory prior to adjusting the repeat interval.

 f. Establish a schedule for ULD functional check and battery or ULD replacement.
AC 20-141 10/05/99

Page 18

 g. Provide for the retention of the DFDR readouts (Operators may retain the actual DFDR

data used for the operational check instead of the data readout or printout. However, the

operator must be able to print out the data or otherwise provide it in a readable format at the

request of the FAA or the NTSB) and the maintenance job card or instructions from the most

recent DFDRS ground operational and functional check. The DFDR data should be retained in

electronic format. However, if the operator does not have the capability to download or retain

the data in electronic format, a computer printout(s) or an oscillograph trace is acceptable.

Provide for retention of these records until they are replaced by records from a subsequent

operational check. The operator must provide for retention of the last operational and

functional check record for at least 6 months after the operator has sold or otherwise

permanently removed the aircraft from its operating certificate.

10. POLICY FOR PART 135 AIRCRAFT. Section 135.152, Flight Recorders, states that

aircraft brought onto the U.S. register after October 11, 1991, are required to meet the

recorder requirements of that section. Several years ago, the Flight Standards Service policy

was that airplanes that were on the U.S. register before October 11, 1991, were taken off, and

were added to the register again after October 11, 1991, did not have to meet the flight

recorder requirements because of the previous registration. As noted in the preamble to the

final rule adopting the 1997 flight recorder requirements, this policy is inconsistent with the clear

language of the rule and with the rules making scheduled commuter airplanes subject to part 121

requirements. The FAA officially changed this policy effective August 1997 (62 FR 38374,

July 17, 1997). Operators of airplanes or rotorcraft that were operating without flight recorders

pursuant to the old policy have until August 18, 2001, to comply with § 135.152. This

compliance time does not appear in the regulation itself to prevent confusion with those aircraft

that are required to comply at the time they are placed on the U.S. register.

James C. Jones

Manager, Aircraft Engineering Division
10/05/99 AC 20-141

Appendix 1

Page 1

APPENDIX 1. STANDARD DATA FORMAT FOR DIGITAL FLIGHT DATA

RECORDERS DATA STREAM FORMAT AND CORRELATION DOCUMENTATION

The Digital Flight Data Recorder System (DFDRS) records flight data in a digital format. Data

is normally grouped into words that are synchronized in a data stream. The data stream must be

correlated to engineering units or to discrete states in order for an accident investigator to use

the data. This appendix provides a standard for the data stream format and correlation

documentation that operators must maintain to aid accident investigators in interpreting recorded

flight data. Acceptable guidelines for documentation of DFDR data content and format are also

available in the Flight Recorder Configuration Standard (FRCS), Document TP13140E. The

FRCS is available from Transport Canada Safety and Security at:

Transportation Development Centre

800 Rene Levesque Blvd. West, Suite 800

Montreal, Quebec, Canada H3B 1X9

Telephone, (514) 283-0000, FAX (514) 283-7158

e-mail: tdccdt@tc.gc.ca

1. Definitions. The following definitions apply to terminology often used in the DFDR

correlation documentation. These definitions are derived from ARINC Characteristic 717-9,

Flight Data Acquisition and Recording System, dated December 3, 1993. An operator using

another data stream format must provide definitions unique to its format in the correlation

documentation.

 a. DFDR Bit Number. The DFDR bit number defines a specific bit location within a

DFDR system word on the output from the DFDR. The DFDR bit number is used to locate the

bits that are dedicated to a given parameter within the word. For example DFDR bit numbers

3-12 indicate bit 3 through bit 12. The lowest bit number is normally the least significant bit.

 b. Lexicon. A dictionary of all Mnemonic Codes and the associated parameters each

represents.

 c. Mnemonic Code. Mnemonic code is an abbreviation of the parameter name. It is

intended to be used in formats where the parameter name is too large. The first eight

characters of the mnemonic code must be used to identify the parameter as described in the

applicable appendix (14 CFR part 121, appendix B or M; 14 CFR part 125 appendix E; or

14 CFR part 135, appendix F). The aircraft manufacturer normally assigns a mnemonic code

to each parameter. This code is normally correlated to the parameter name in the aircraft

manufacturer’s interface control document. However, a modifier or an operator may assign a

mnemonic code to an
AC 20-141 10/05/99

Appendix 1

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APPENDIX 1. STANDARD DATA FORMAT FOR DIGITAL FLIGHT DATA

RECORDERS DATA STREAM FORMAT AND CORRELATION DOCUMENTATION

(CONTINUED)

added parameter. The mnemonic code must uniquely identify the parameter relative to all other

parameters being recorded by the DFDR. Additional characters may be necessary to uniquely

identify the parameter as installed on the aircraft. Table 1-5 contains a lexicon of some typical

mnemonic codes.

 d. Parameter Name. The name of the function being recorded. The documentation must

contain a means to correlate each recorded parameter name to those in the applicable appendix

(part 121, appendix B or M; part 125 appendix E; or part 135, appendices B through F).

Where possible, the parameter name should correlate to the aircraft manufacturer’s interface

control documentation. Sufficient information must be contained in the parameter name to make

it unique and to convey information on its source.

 e. Range. The full range of a parameter (minimum to maximum) expressed in engineering

units (E.U.). Where the parameter range accommodated in the aircraft exceeds the parameter

range specified in the regulations, (e.g., pressure altitude in large aircraft) the applicant should

provide for recording the range accommodated in the aircraft. Enter N/A for discrete

parameters.

 f. Signal Source. The aircraft subsystem, or the dedicated transducer or signal conditioner,

installed primarily to provide the signal for the DFDR, FDAU, or DFDAU (or equivalent).

 g. Superframe Cycle. A subdivision of a given word slot address in a subframe. This

typically provides 16 additional addresses. A counter provides the cycle number reference.

The cycle number must be documented as a parameter.

 h. Word Slot. The location of a 12-bit word within the subframe.

2. Data Stream Format. The data stream format defines where an analyst must look in the

DFDR output to find a selected parameter or other information. Most DFDR data are encoded

using the specifications of ARINC 573 or ARINC 717. Although these ARINC data bus

encoding systems do not specify the date format, they provide the framework within which the

data is formatted. They generate 64 12-bit words per second yielding a bit rate of 768 bits per

second. The word rate may vary in multiples of two, i.e. 32, 64, 128, 256, or 512. The data is

organized into frames that are repeated every four seconds. Each frame consists of four

subframes that occupy one second each in the data stream. The first word in each subframe

normally provides the frame synchronization pattern. The data stream format should enable the

analyst to locate header information and parameter information in the DFDR output.
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APPENDIX 1. STANDARD DATA FORMAT FOR DIGITAL FLIGHT DATA

RECORDERS DATA STREAM FORMAT AND CORRELATION DOCUMENTATION

(CONTINUED)

 a. Header Information. For DFDR’s that conform to ARINC specifications, the following

information must be stored in a header file. For other DFDR frame structures, the number of

subframes per frame must be omitted and the frame structure must be uniquely described.

 (1) Aircraft Make and Model.

 (2) Aircraft Serial Number.

 (3) DFDR Make and Model/Part Number.

 (4) Number of subframes per frame.

 b. Record Information. The following information must be provided for each record; except

that if each subframe is identical, it may be provided only once:

 (1) Bits in the DFDR Word.

 (2) Number of DFDR Words in a Subframe.

 (3) Time duration of the subframe (seconds).

 c. Parameter Information. The identification for each parameter must include:

 (1) Parameter Name – must be unique from all other parameters recorded.

 (2) Mnemonic Code – a common abbreviation for the parameter.

 d. Parameter Location. Both component(s)and timing information must be provided for

each parameter sample. Usually there is only one component. For samples having more than

one component the components must be ordered from least significant to most significant in the

data stream. Each sample location for a parameter must have the same total number of bits.

The following items must be provided for a parameter sample location:

 (1) Subframe Number.

 (2) Word Number.

 (3) Bit Numbers.

 (4) If superframe cycles are used, also provide:
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APPENDIX 1. STANDARD DATA FORMAT FOR DIGITAL FLIGHT DATA

RECORDERS DATA STREAM FORMAT AND CORRELATION DOCUMENTATION

(CONTINUED)

 (a) Cycle counter name.

 (b) Cycle numbers.

3. Lexicon of Mnemonic Codes. If mnemonic codes are used, a lexicon of these codes must

be provided.

4. Engineering Unit (E.U.) Conversion. Engineering unit (E.U.) conversions must convert

decimal counts to the parameter value measured. Where the parameter is used by the pilot in

flight (e.g. airspeed, altitude, and heading), the conversion must be correlated to the value

shown to the pilot. Other values must be correlated to values sensed by the aircraft. Where an

E.U. conversion results in an interim parameter (e.g., ac voltage ratio No.1, frequency, dc

voltage ratio No.2, potentiometer, or synchro angle) the conversion formula that converts this

interim parameter to the actual parameter must also be provided. Each recorded parameter

must be converted to an E.U. Both signage (whether or not the raw data contains a plus or

minus sign and the location of the sign in the parameter bits) and raw data range must be

provided. Standardized signage is provided in Table 1-1. Instructions must be provided to

enable the accident investigator to convert the recorded data to E.U.

Table 1-1. Standardized Sign Convention

Parameter Sign

Aircraft Pitch Attitude – Aircraft Nose Up

(ANU)

+

Aircraft Roll Attitude – Right Wing Down

(RWD)

+

Flight Control Surface – Trailing Edge Up

(TEU)

+

Acceleration See Section 7.1, ARINC 717-9

Glide Slope – Fly Up Indication +

Localizer – Fly Left Indication +

Acceptable conversion equations are as follows:

 a. Linear Equation:

 E.U. = A0 + A1 * CNTS10

 where: E.U. is the value in engineering units

 A0 is the number of E.U. when the CNTS10 equals zero

 A1 is the slope of the line in engineering units per decimal count

 CNTS10 is the number of binary or binary coded decimal counts
10/05/99 AC 20-141

Appendix 1

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 converted to decimal counts

APPENDIX 1. STANDARD DATA FORMAT FOR DIGITAL FLIGHT DATA

RECORDERS DATA STREAM FORMAT AND CORRELATION DOCUMENTATION

(CONTINUED)

 b. Piece-wise Linear Equation. In some instances it may be necessary to correlate the data

using multiple linear equations. For example: the data of Figure 1-1. was obtained using two

linear equations as follows:

 For Altitude (E.U.) < 500 feet For Altitude (E.U.) > 500 feet

 A0 = (- 0.002) A0 = (- 0.29673)

 A1 = (0.200231) A1 = (0.013351)

 where: < indicates equal to or less than

 > indicates greater than

 c. Polynomial Equation.

 E.U. = A0 + A1 * CNTS10 + A2 * CNTS10

2

 + ... Ax * CNTS10

x

 where: E.U. is the value in engineering units

 CNTS10 is the number of binary or binary coded decimal counts converted to

 decimal counts

 A0 is the number of E.U. when the CNTS10 equals zero

 A1, A2, ... Ax are coefficients developed by a curve fit

 d. Unique Equation. Where a unique equation applies, explicit documentation must be

developed at the time of certification, and approved by the FAA.

5. E.U. Data Correlation. An acceptable procedure to correlate the recorded data to the data

derived from the conversion equation follows:

 a. Set or read the device being measured (radio altimeter altitude for example) to a known

fixed data point.

 b. Record the data in the Raw Data (E.U.) column of the Correlation Table 1-3.

 c. Record the decimal counts from the DFDR record in the CNTS10 column of the

Correlation Table (See Table 1-3).
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APPENDIX 1. STANDARD DATA FORMAT FOR DIGITAL FLIGHT DATA

RECORDERS DATA STREAM FORMAT AND CORRELATION DOCUMENTATION

(CONTINUED)

NOTE: The DFDR normally records counts in a binary format. Most

equipment manufacturers provide a digital output port and test

equipment to access the data. Data can be displayed in either binary,

octal, or hexadecimal format with octal being the most common.

Convert the counts to decimals using instructions provided by the

equipment manufacturer.

 d. Repeat steps 1 through 3 above until a sufficient number of data points have been

collected for correlation.

Note: The number of required data points will vary depending upon the

parameter and the transducer. As a minimum, three data points must be

recorded for linear equation parameters, one at the mid-point (or null

point) and the others at each end point of the range for the parameter. A

minimum of six data points must be recorded for polynomial equation

parameters For piece-wise linear equations, a minimum of three data

points must be recorded for each linear segment of the equation.

e. Derive the E.U. value for each recorded CNTS10 value using the conversion equation or

method provided. Record the derived value for each data point.

 f. The tabulated raw data and the derived data must also be plotted to confirm the

prediction capability of the equation (linear, piece-wise linear, polynomial or unique). The plot

must cover the full operating range for the parameter. See Figure 1-1 for an example plot. In

the example of Figure 1-1, the data is so closely correlated (correlation coefficient = 0.99985)

that the raw data and the derived data appear to be superimposed on each other.
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APPENDIX 1. STANDARD DATA FORMAT FOR DIGITAL FLIGHT DATA

RECORDERS DATA STREAM FORMAT AND CORRELATION DOCUMENTATION

(CONTINUED)

Figure 1-1. An Example Plot of the Radio Altimeter in Feet Versus Decimal Counts

DFDR Radio Altitude Conversion

0

500

1000

1500

2000

2500

60

534999

151819882482273928883088339837244057

Counts

Radio Alt (ft.)

Raw Data

Derived Data

6. Discrete Decipher Logic: The correlation documentation must contain decipher logic for

discrete parameters. The decipher logic must identify the status of the discrete represented by

each binary state (e.g., “0” =OFF, “1”=ON). In instances where a group of discrete states is

represented by multiple binary bits, the entire discrete word must be presented in the correlation

document. See Table 1-2. The word slot, subframe, and bit logic for the specific discrete

codes must be identified in the documentation

Table 1-2. Example of Grouped Discrete Codes Decipher Logic

Word Slot _____________ Subframe __________________

Discrete Status Discrete Codes

7 6 5 4 3 2 1

A/P Mode Throttle “OFF” 1 1 0 0 0 0 0

A/P Mode Throttle “RETARD” 1 1 0 0 0 0 1

A/P Mode Throttle “CLAMP” 1 1 0 0 0 1 0

A/P Mode Throttle “SPD/MCH,ALPHA” 1 1 0 0 0 1 1

A/P Mode Throttle “SPD/MCH,FLAP” 1 1 0 0 1 0 0

A/P Mode Throttle “SPD/MCH,SLAT” 1 1 0 0 1 0 1

A/P Mode Throttle “SPEED” 1 1 0 0 1 1 0

A/P Mode Throttle “EPR LIMIT” 1 1 0 0 1 1 1

A/P Mode Throttle “SPD/EPR LIMIT” 1 1 0 1 0 0 0

7. Validation of Engineering Unit Correlation: Calculate the correlation coefficient between the

raw data and the derived data. Table 1-3 may be used to aid this calculation. The correlation

coefficient must be calculated as follows:
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APPENDIX 1. STANDARD DATA FORMAT FOR DIGITAL FLIGHT DATA

RECORDERS DATA STREAM FORMAT AND CORRELATION DOCUMENTATION

(CONTINUED)

r = N * Σ( x*y) - Σx * Σy

 { [N * Σx

2

 - (Σx)2 ] * [N * Σy

2

 - (Σy)2] }1/2

where: r = correlation coefficient

N = number of data points

x = raw data (E.U.)

y = derived data (E.U.)

Σ indicates the sum of the values that follow (e.g., Σx equals the sum of

all x values)

Table 1-3 Correlation Table Decimal Counts to Engineering Units

Parameter No. ____ Parameter _____________________________________

Conversion Method Linear Polynomial Unique

A0 ___________ Unique Equation Reference:__________

A1 ___________ ___________________________________

A2 ___________

A3 ___________

A4 ___________

A5 ___________
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Page 9

Data Point No. Raw Data (E.U.) CNTS10 Derived Value (E. U.)

1

2

3

4

5

6

7

8

9

10
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APPENDIX 1. STANDARD DATA FORMAT FOR DIGITAL FLIGHT DATA

RECORDERS DATA STREAM FORMAT AND CORRELATION DOCUMENTATION

(CONTINUED)

Table 1-4 Correlation Coefficient Calculation

Parameter No. ____ Parameter Name ________________________________

Mnemonic Code _____________

Parameter Word Location ___________________

Subframe _______________

Superframe Cycle ___________________

Assigned Bits (1 through 12) __________________

Range (E.U.) ______________________

Sign Convention _______________________________

Correlation Coefficient _________

 a. N * Σ( x*y) = __________

 b. Σx * Σy = __________

Data Point

No.

x

Raw Data (E.U.)

y

Derived

Value (E.U.)

x

2

y

2

x * y

1

2

3

4

5

6

7

8

9

10

N = Σx = Σy = Σx

2 

 = Σy

2

 = Σ( x*y) =
10/05/99 AC 20-141

Appendix 1

Page 11

APPENDIX 1. STANDARD DATA FORMAT FOR DIGITAL FLIGHT DATA

RECORDERS DATA STREAM FORMAT AND CORRELATION DOCUMENTATION

(CONTINUED)

 c. Subtract (b) from (a)

 N * Σ( x*y) - Σx * Σy = ____________

 d. N * Σx

2

 = __________

 e. Square the sum of x (Σx) and subtract this square from (d)

 [N * Σx

2

 - (Σx)

2

 ] = (4) - Column 4 = __________

 f. N * Σy

2

 = ___________

 g. Square the sum of y (Σy) and subtract this square from (f)

 [N * Σy

2

 - (Σy)

2

 ] = __________

 h. Subtract (g) from (f)

 [N * Σx

2

 - (Σx)

2

 ] * [N * Σy

2

 - (Σy)2] = ____________________

 i. Take the square root of (h)

 { [N * Σx

2

 - (Σx)2 ] * [N * Σy

2

 - (Σy)2]}1/2 = ____________________

 j. Divide (c) by (i)

 r = ________N * Σ( x*y) - Σx * Σy________ = ____________________

 { [N * Σx

2

 - (Σx)2 ] * [N * Σy

2

 - (Σy)2] }1/2

The correlation coefficient (r) must not be less than 0.9

TABLE 1-5. Typical Lexicon of

Mnemonic Codes

CODE PARAMETER

AOA Angle of Attack

CAS Calibrated Airspeed

ANU Aircraft Nose Up

TEU Trailing Edge UP

SPD Speed

A/P Autopilot

EPR Engine Pressure Ratio

THRTL Throttle

MCH MACH
AC 20-141 10/05/99

Appendix 1

Page 12

RWD Right Wing Down
10/05/99 AC 20-141

Appendix 2

Page 1

APPENDIX 2. DIGITAL FLIGHT DATA RECORDER REQUIREMENTS SCHEDULE

1. Turbine-engine powered transport category airplanes operating under the provisions of 14

CFR part 121. For scheduling of DFDR system installations, there are six categories of

turbine-engine powered transport category airplanes. Affected airplanes in the first four

categories are those requiring post-production retrofits. The other two categories include

airplanes that will receive the system during production. Airplanes requiring retrofit are grouped

by the date of manufacture and by the particular equipment installed at the time the DFDR

Notice of Proposed Rule Making was published (July 16, 1996). Airplanes upgraded during

production are grouped by manufacture dates. The categories are as follows:

 a. Airplanes manufactured on or before October 11, 1991, that were not equipped with

Flight Data Acquisition Units (FDAU) as of July 16, 1996. These airplanes must be upgraded

from their current eleven (11) parameter recording capability to record eighteen (18)

parameters. The retrofit must be accomplished by the next heavy maintenance check after

August 18, 1999, but no later than August 20, 2001.

 (1) The parameters must be recorded to the range and accuracy specifications of part

121. appendix B (or part 125, appendix D).

 (2) Recording of lateral acceleration, parameter (18), for airplanes having more than two

engines is not required unless sufficient capacity is available on the installed recorder.

 (3) Because of capacity limitations of some DFDR’s, certain split flight control

parameters (e.g., aileron, split elevator, rudder) may be recorded using the bellcrank or a single

control wheel/column or pedal position instead of recording the position of both control

wheel/column or sets of rudder pedals. The following parameters may be recorded from a

single source. However, sensors must be located so as to allow for the differentiation between

cockpit flight control inputs and flight control surface position:

 (a) Parameter (12) Pitch control input.

 (b) Parameter (13) Lateral control input.

 (c) Parameter (14) Rudder pedal input.

 (d) Parameter (15) Primary pitch control surface position.

 (e) Parameter (16) Primary lateral control surface position.

 (f) Parameter (17) Primary yaw control surface position.
AC 20-141 10/05/99

Appendix 2

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APPENDIX 2. DIGITAL FLIGHT DATA RECORDER REQUIREMENTS SCHEDULE

(CONTINUED)

 b. Airplanes manufactured on or before October 11, 1991, that were equipped with FDAU

as of July 16, 1996. These airplanes must be upgraded to record 22 parameters. The retrofit

must be accomplished by the next heavy maintenance check after August 18, 1999, but no later

than August 20, 2001.

 (1) The parameter specifications of 14 CFR part 121, appendix M or 14 CFR part 125,

appendix E apply to all parameters.

 (2) Because of capacity limitations of some DFDR’s, certain split flight control

parameters may be recorded using the bellcrank or a single control wheel/column or pedal

position instead of recording the position of both control wheel/column or sets of rudder pedals.

The following parameters may be recorded from a single source. However, sensors must be

located so as to allow for the differentiation between cockpit flight control inputs and flight

control surface position:

 (a) Parameter (12) Pitch control input.

 (b) Parameter (13) Lateral control input.

 (c) Parameter (14) Rudder pedal input.

 (d) Parameter (15) Primary pitch control surface position.

 (e) Parameter (16) Primary lateral control surface position.

 (f) Parameter (17) Primary yaw control surface position.

 c. Airplanes manufactured on or before October 11, 1991, that were equipped with

ARINC 717 DFDAU or equivalent as of July 16, 1996. These airplanes must be upgraded to

record 22 parameters. The retrofit must be accomplished by August 20, 2001.

 (1) The parameter specifications of part 121, appendix M, or part 125, appendix E

apply to all parameters.

 (2) Because of capacity limitations of some DFDR’s, certain split flight control

parameters

(e.g., pitch control input, lateral control input, and rudder pedal input) may be recorded using

the bellcrank or a single control wheel/column or pedal position instead of recording the position

of both control wheel/column or sets of rudder pedals. The following parameters may be

recorded from a single source. However, sensors must be located so as to allow for the

differentiation between cockpit flight control inputs and flight control surface position:
10/05/99 AC 20-141

Appendix 2

Page 3

APPENDIX 2. DIGITAL FLIGHT DATA RECORDER REQUIREMENTS SCHEDULE

(CONTINUED)

 (a) Parameter (12) Pitch control input.

 (b) Parameter (13) Lateral control input.

 (c) Parameter (14) Rudder pedal input.

(3) Additional parameters must be recorded if the capacity of the recording system permits.

The recording system refers to the already installed DFDAU and DFDR plus any necessary

DFDAU and DFDR installed in order to record parameters (1) through (22). This requirement

only applies if the data source is already installed and connected to the recording system. For

example, if a ground proximity warning system is already installed in the airplanes and the wiring

is in place to connect it to the DFDAU and the DFDR system has sufficient available recording

capacity (data bit stream slots and memory), then parameter (35), ground proximity warning

system, must be recorded. Where a choice is available, the applicant should select additional

parameters to be recorded in priority order if practical. Keeping in mind the generic form of the

parameter listing, it may be appropriate to deviate from the order of the parameter list to record

a non-mandatory parameter or parameters to monitor an operational or system characteristic

unique to that make and model airplane.

 (4) All airplanes equipped with ARINC 717 DFDAU that were required to have a

DFDR system installed by section 121.343(e) or 125.225(e) must continue to comply with

section 121. 343(e) or 125.225(c) until they are retrofitted.

 d. Airplanes manufactured after October 11, 1991, but before August 18, 2000. These

airplanes must be upgraded to record 34 parameters. The retrofit must be accomplished by

August 20, 2001.

 (1) The parameter specifications of part 121, appendix M (part 125, appendix E) apply

to all parameters.

 (2) Because of capacity limitations of some DFDR’s, certain split flight control

parameters (e.g., pitch control input, lateral control input, and rudder pedal input) may be

recorded using the bellcrank or a single control wheel/column or pedal position instead of

recording the position of both control wheel/column or sets of rudder pedals. The following

parameters may be recorded from a single source. However, sensors must be located so as to

allow for the differentiation between cockpit flight control inputs and flight control surface

position:

 (a) Parameter (12) Pitch control input.

 (b) Parameter (13) Lateral control input.
AC 20-141 10/05/99

Appendix 2

Page 4

APPENDIX 2. DIGITAL FLIGHT DATA RECORDER REQUIREMENTS SCHEDULE

(CONTINUED)

 (c) Parameter (14) Rudder pedal input.

 (3) Additional parameters must be recorded if the capacity of the recording system

permits. The recording system refers to the already installed DFDAU and DFDR plus any

necessary DFDAU and DFDR installed in order to record parameters (1) through (34). This

requirement only applies if the data source is already installed and connected to the recording

system. For example, if a ground proximity warning system is already installed in the airplanes

and the wiring is in place to connect it to the DFDAU and the DFDR system has sufficient

available recording capacity (data bit stream slots and memory), then parameter (35) must be

recorded. Where a choice is available, the applicant should select the additional parameters to

be recorded in priority order if practical. Keeping in mind the generic form of the parameter

listing, it may be appropriate to deviate from the order of the parameter list to record a nonmandatory parameter or parameters to monitor an operational or system characteristic unique to

that make and model airplane.

 e. Airplanes manufactured after August 18, 2000, but before August 20, 2002. The

airplanes must be equipped to record 57 parameters.

 (1) The parameter specifications of part 121, appendix M or part 125, appendix E

applies to all parameters.

 (2) Additional parameters must be recorded if the capacity of the recording system

permits. The recording system refers to the already installed DFDAU and DFDR plus any

necessary DFDAU and DFDR installed in order to record parameters (1) through (57). This

requirement only applies if the data source is already installed and connected to the recording

system. For example, if a ground proximity warning system is already installed in the airplane

and the wiring is in place to connect it to the DFDAU and the DFDR system has sufficient

available recording capacity (data bit stream slots and memory), parameter (35) must be

recorded. Where a choice is available, the applicant should select the additional parameters to

be recorded in priority order, if practical. Keeping in mind the generic form of the parameter

listing, it may be appropriate to deviate from the order of the parameter list to record a nonmandatory parameter or parameters to monitor an operational or system characteristic unique to

that make and model airplane.

 f. Airplanes manufactured after August 19, 2002. These airplanes must be equipped to

record 88 parameters. The parameter specifications of part 121, appendix M, or part 125,

appendix E, apply to all parameters.

2. Turbine-engine powered airplanes having passenger seating of 10 to 19 seats operating

under the provisions of 14 CFR part 121. There are three categories of 10 to 19 passenger

airplanes for scheduling of DFDRS installations.
10/05/99 AC 20-141

Appendix 2

Page 5

APPENDIX 2. DIGITAL FLIGHT DATA RECORDER REQUIREMENTS SCHEDULE

(CONTINUED)

 a. Airplanes (10 to 19 passengers) brought onto the U. S. register or foreign-registered

airplanes added to an operator’s U. S. operations specifications after October 11, 1991, but

manufactured on or before August 18, 2000. In order to operate under part 121, these

airplanes must be equipped with a DFDR system recording 18 parameters by the next heavy

maintenance check or equivalent after

August 18, 1999, but before August 20, 2001. The parameter specifications of part 135,

appendix B applies to all parameters. Where part 135, appendix B does not provide a

specification (range, accuracy or sampling interval) the specification of appendix M must be

used. In order to operate under part 135, these airplanes must be equipped with a 25 hour

DFDRS that record parameters listed in part 135, appendix B.

 (1) Only one parameter in each of the following parameter pairs need be to recorded:

 (a) Parameter (12), or parameter (15).

 (b) Parameter (13), or parameter (16).

 (c) Parameter (14), or parameter (17).

 (2) Recording of lateral acceleration for airplanes having three or more engines is not

required unless sufficient capacity is available on the installed recorder.

 (3) Because of parameter capacity limitations of the modified DFDR, certain split flight

control parameters (e.g., aileron, split elevator) may be recorded using the bellcrank or a single

surface or pedal position instead of recording the position of both surfaces or pedals. The

following parameters may be recorded from a single source:

 (a) Parameter (12), Pitch control input.

 (b) Parameter (13), Lateral control input.

 (c) Parameter (14), Rudder pedal input.

 (d) Parameter (15), Primary pitch control surface position.

 (e) Parameter (16), Primary lateral control surface position.

 (f) Parameter (17), Primary yaw control surface position.
AC 20-141 10/05/99

Appendix 2

Page 6

 (4) If the FDAU and the DFDR have the capacity to record additional parameters, the

following parameters must be selected for recording in the order listed:

APPENDIX 2. DIGITAL FLIGHT DATA RECORDER REQUIREMENTS SCHEDULE

(CONTINUED)

 (a) Parameter (19), Pitch Trim Position or Parameter (82), Cockpit Trim Control

Input Position - Pitch.

 (b) Parameter (20), Trailing Edge Flap or Cockpit Flap Control Selection.

 (c) Parameter (21), Leading Edge Flap or Cockpit Flap Control Selection.

 (d) Parameter (22), Each Thrust Reverser Position (or equivalent for propeller

airplane).

 b. Airplanes (10 to 19 passengers) manufactured after August 18, 2000, but before

August 20, 2002. These airplanes operated under part121 must be equipped with a DFDRS

that records 57 parameters. The parameter specifications of part 121, appendix M applies to

all parameters. Additional parameters must be recorded if sufficient recording capacity exists in

the DFDRS.

 c. Airplanes (10 to 19 passengers) manufactured after August 19, 2002. These airplanes

must be equipped with the 88-parameter system. The parameter specifications of part 121,

appendix M applies to all parameters.

3. Airplanes (10 to 30 passengers) operated under part 135 and manufactured after

August 18, 2000, but before August 20, 2002. These airplanes operated under part 135 must

be equipped with a 57-parameter DFDRS by August 20, 2001. The parameter specifications

of part 135, appendix F applies to all parameters. Additional parameters must be recorded if

sufficient recording capacity exists in the DFDRS.

4. Airplanes (10 to 30 passengers) operated under Part 135 and manufactured after

August 19, 2002. These airplanes, operated under part 135, must be equipped with the 88

parameter system. The parameter specifications of 14 CFR part 135 appendix F applies to all

parameters.

5. Multiengine turbine-powered 10 to 19 passenger rotorcraft brought onto the U.S. register or

registered outside the United States and brought onto an operators U.S. operations

specification after October 11, 1991. These rotorcraft must be upgraded to a 25-hour DFDRS

that must record the parameters listed in part 135, appendix H.

6. Stage 2 airplanes that are subject to section 91.801(c) until January 1, 2000. If these

airplanes are allowed to continue operating on or after January 1, 2000, they must, at that time,
10/05/99 AC 20-141

Appendix 2

Page 7

comply with the applicable DFDRS requirements of section 121.344 in order to continue

operation.
AC 20-141 10/05/99

Appendix 2

Page 8

APPENDIX 2. DIGITAL FLIGHT DATA RECORDER REQUIREMENTS SCHEDULE

(CONTINUED)

7. U.S. registered aircraft operated by a foreign carrier under part 129. These aircraft must

have a DFDRS that records the parameters that would be required under part 121, 125, or

135 as applicable to the aircraft.

8. Airplanes not required to have a DFDR. The following airplanes manufactured before

August 18, 1997, when operated under part 121 are not required to have a DFDR but must

continue to comply with the DFDR requirements of §121.343 or §135.152 as applicable:

Beech 99 series Beech 1300

Beech 1900C CASA C-212

*Convair 580 *Convair 600

*Convair 640 ΦdeHavilland DHC-6

*deHavilland DHC-7 Dornier 228

Embraer EMB 110 Fairchild Airplanes SA-226

*Fairchild Industries FH227 *Fokker F-27 (except Mark 50)

*Fokker F-28 Mark 1000 and Mark 4000 *Gulfstream Aerospace G-159

Hawker Siddley HS-748 Jetstream 3101 and 3201

*Maryland Air Industries F27 *Mitsubishi YS-11

*Short Bros. SD3-30 and SD3-60 Fairchild SA-226

*Lockheed Electra 10-A, 10-B, 10-E, and L-188

Any airplane that meets the Stage 2 noise levels of part 36 and is subject to section 91.801(c)

may continue to operate in compliance with Section 121.343 until January 1, 2000.

* Indicates that, when operated under part 125, these aircraft need not comply with the

DFDRS requirements of section 125.226, but must continue to comply with those of section

125.225.

Φ Indicates that, these aircraft manufactured before August 18, 1997, when operated under

part 135, need not comply with section 135.152. Aircraft manufactured on or after that date

must comply.
10/05/99 AC 20-141

Appendix 3

Page 1

APPENDIX 3. TYPICAL CERTIFICATION BASIS FOR DFDR RETROFIT

14 CFR,

Section—

General

14 CFR Part

23 Section

14 CFR Part 25

Section

14 CFR

Part 27

Section

14 CFR

Part 29

Section Subject Comment

21.97 Approval of major

changes in type

design

Substantiating data and

descriptive data

21.305(b) Approval of

materials, parts, and

appliances

Use for TSO approved

equipment

23.25 25.25 27.25 29.25 Weight Limits Weight & Balance

25.27 27.27 29.27 Center-of-gravity

limits

Weight & Balance

23.603 25.603 27.603 29.603 Materials Use of TSO approved

equipment

23.1359(c) 25.869(a)(4) 27.1365(

c)

29.1359(

c)

Fire Protection:

Systems

Insulation on electrical

wire must be selfextinguishing

23.1301(a) 25.1301(a) 27.1301 29.1301 Function and

installation

Appropriate for intended

function

23.1301(b) 25.1301(b) Labeled for identification

23.1301(c) 25.1301(c) Installed according to

limitations

23.1301(d) 25.1301(d) Parameter correlation test

and documentation

23.1309(b)(1) 25.1309(a) 27.1309 29.1309 Equipment, systems,

and installations

Foreseeable operating

conditions

23.1309(b)(2) 25.1309(b) Failure conditions

23.1309(b)(3) 25.1309(c) Warning information
AC 20-141 10/05/99

Appendix 3

Page 2

APPENDIX 3. TYPICAL CERTIFICATION BASIS FOR DFDR RETROFIT (CONTINUED)

14 CFR,

Section—

General

14 CFR Part

23 Section

14 CFR Part 25

Section

14 CFR

Part 27

Section

14 CFR

Part 29

Section Subject Comment

23.1309(c) 25.1309(e) Electrical loads analysis -

power loads in probable

operating conditions and

durations

23.1309(e) 25.1309(g) Critical environmental

conditions

23.1351(a) 25.1351(a) 27.1351 29.1351 Electrical Systems

and Equipment,

General

Electrical loads analysis

23.130(c) 25.1353(a) 27.1365 Electrical systems

and installations

Does not adversely affect

simultaneous operation

23.1365 25.1353(b) Cables, damage to

essential circuits

23.1357 25.1357(a) 29.1357 Circuit protective

devices

Circuit breakers, wiring

faults, and system

malfunctions

23.1431 25.1431(a) 29.1431 Electronic

equipment

Critical environmental

conditions

23.1437 25.1431(b) Independent sources of

power

23.1431(b) 25.1431(c) Adverse effect on other

equipment

23.1459(a)(1) 25.1459(a)(1) 27.1459 29.1459 Flight recorders Airspeed, altitude, and

directional data

23.1459(a)(2) 25.1459(a)(2) Vertical acceleration

sensor

23.1459(a)(3) 25.1459(a)(3) Electrical power

23.1459(a)(4) 25.1459(a)(4) Aural and visual means of

preflight check

23.1459(a)(5) 25.1459(a)(5) Automatic means to stop
10/05/99 AC 20-141

Appendix 3

Page 3

APPENDIX 3. TYPICAL CERTIFICATION BASIS FOR DFDR RETROFIT (CONTINUED)

14 CFR,

Section—

General

14 CFR Part

23 Section

14 CFR Part 25

Section

14 CFR

Part 27

Section

14 CFR

Part 29

Section Subject Comment

25.1459(a)(6) Time of each radio

transmission

23.1459(b) 25.1459(b) Located and mounted

23.1459(c) 25.1459(c) Correlation Performed to

Section 121.344(j) under

intended function to

operating rule.

23.1459(d)(1) 25.1459(d)(1) Bright orange

23.1459(d)(2) 25.1459(d)(2) Reflective tape

23.1459(d)(3) 25.1459(d)(3) ULD

23.1459(e) 25.1459(e) Novel or unique

characteristics

23.1529 25.1529 27.1529 29.1529 Instructions for

continued

airworthiness

Description, servicing,

troubleshooting, testing,

and repair

10/05/99 AC 20-141

Appendix 4

Page 1

APPENDIX 4. TYPICAL FLIGHT SEQUENCE DATA RECORD FOR TYPE

INSPECTION FLIGHT TEST - 36 PARAMETER DFDRS INSTALLATION

1. Begin recording prior to takeoff. Record:

a. Prior to takeoff record time of flight control check (hold flight controls at full travel for 2

to 5 seconds, each position).

b. Takeoff Flap Setting.

c. Takeoff thrust setting.

d. Brake release time.

e. Rotation Speed (VR) and time of rotation.

f. Aircraft attitude after rotation.

2. During stabilized climb (wings level) after takeoff record:

a. Altitude and time at which climb stabilized.

b. Airspeed.

c. Vertical speed.

d. Pitch attitude.

e. Displayed angle of attack.

f. Heading (note true or magnetic).

3. During Level Flight (wings level) at maximum operating limit speed (VMO./MMO) or at VMAX

record:

a. Altitude and time at start of level flight.

b. Airspeed.

c. Ground speed and time at which recorded (three times).

d. Outside or total air temperature.

e. Automatic Flight Control System (AFCS) Mode and engagement status including

autothrottle.

f. Pitch attitude.

g. Displayed angle of attack.

h. Heading (note true or magnetic).

i. Drift angle and time at which recorded (three times).

j. All displayed engine performance parameters for each engine.

k. Altitude and time at end of level flight.

4. During a banked turn (90o to 180o heading change) record:

a. Altitude, heading and time at beginning of turn.

b. Stabilized roll attitude (bank angle).

c. Altitude, heading and time at end of turn.
AC 20-141 10/05/99

Appendix 4

Page 2

APPENDIX 4. TYPICAL FLIGHT SEQUENCE DATA RECORD FOR TYPE

INSPECTION FLIGHT TEST - 36 PARAMETER DFDRS INSTALLATION

(CONTINUED)

5. During stabilized (wings level) descent, record:

a. Altitude and time at which descent initiated.

b. Airspeed.

c. Pitch attitude.

d. Displayed angle of attack.

e. Heading (note true or magnetic).

f. Altitude and time at which leveled off.

6. During approach at level flight (wings level) deploy flaps throughout the flap operating range

in all available settings (or at 5o increments) and hold for 5 seconds at each setting. Record:

a. Altitude and time at beginning of flap deployment sequence.

b. Flap setting and time when each setting is reached.

c. Altitude and time at end of flap deployment sequence.

7. During final approach, record:

a. Altitude and time at beginning of final.

b. Radio altitude and time at which recorded (three points).

c. Localizer Deviation and time at which recorded (three times).

d. Glide Slope Deviation and time at which recorded.

e. Time of Outer Marker passage.

f. Time of Landing Gear Deployment.

g. Final flap setting.

h. Time of Inner Marker passage.

8. During landing and rollout, record:

a. Time when thrust reversers deployment sequence was initiated.

b. Ground spoiler or speed brake setting and time ground spoiler deployed.

9. During all flight phases, record:

a. Time of any three radio transmissions from each flightcrew position.

b. Any warning or caution lights that illuminated and the time at which they illuminated.
10/05/99 AC 20-141

Appendix 5

Page 1

APPENDIX 5. TYPICAL REASONABLENESS AND QUALITY CHECK

INSTRUCTIONS

1. General. The operator must accomplish a reasonableness and quality check of the recorded

flight data to ascertain that the data is being recorded correctly and that noise and data dropouts

do not interfere with the ability to interpret the recorded data. The check may be performed

using data that is in electronic format or using hardcopy data. If a hardcopy printout is used,

data traces should also be available. The check must be performed using data that has been

extracted in engineering units. Octal, binary coded decimal, or hexadecimal coded data does

not provide the analyst a clear understanding of how the parameters are varying and how they

are correlated to each other.

2. Checklist. The analyst must use a checklist to assure that all necessary checks have been

accomplished. The checklist must refer the analyst to troubleshooting or repair procedures

should a suspect parameter be identified.

3. Functional Checks. The reasonableness and quality check is only a part of the checks

needed in order to ascertain that flight data is being properly recorded. The analyst should also

perform functional checks of parameters that were not exercised during the period(s) of flight

from which the stored data was extracted. The operator may include a check of recorded flight

data during a systems check of the system providing the data. Or, the operator may include a

functional exercise of the system and a flight data extraction during the reasonableness and

quality check. The objective is to ensure that all parameters are checked periodically; either at

the frequency that the recorded flight data is checked or at the frequency at which the system

that provides the data is checked. Some examples of parameters that do not change during a

typical flight are: Fire Warning Discrete, Master Warning Discrete, and Hydraulic Pressure

Low.

4. Flight Segment Selection. The data to be used by the analyst should be extracted from both

the takeoff and the landing phase of flight. During the cruise segment of a flight the parameters

remain steady, and therefore movement of related parameters cannot be correlated. The

takeoff and landing segments of flight provide the analyst an opportunity to observe data that is

changing as the aircraft climbs, descends, accelerates, decelerates, and banks or turns.

Furthermore, many parameters that are not exercised during the cruise segment are exercised

during the takeoff and landing segments.

5. Sign Conventions. Each aircraft has a pre-established sign convention for the direction of

movement of its flight control surfaces. It is imperative that the analyst be able to confirm

proper direction of movement and not just verify movement. Therefore, the sign convention

should be included in the checklist or the analyst should review the assigned sign conventions

before beginning the check.
AC 20-141 10/05/99

Appendix 5

Page 2

6. Failed Parameters. The analyst should examine the extracted data to determine if

parameters that normally vary in flight, e.g. flight controls, flight control surface positions, and

heading, are indeed varying. Pegged or unmoving parameter values are

APPENDIX 5. TYPICAL REASONABLENESS AND QUALITY CHECK

INSTRUCTIONS (CONTINUED)

indications of an inoperative sensor or other failure. Accelerometers tend to fail in the “pegged”

position. If the accelerometer trace is unmoving throughout all segments of flight checked,

check to see if it indicates maximum or minimum acceleration. An accelerometer failure

indicating a mid-point value is uncommon.

7. Correlation to Other Parameters. The reasonableness check should include a check of the

correlation between parameters that depend upon each other. For example: if ROLL increases,

a turn is indicated and HEADING should begin to change soon after the increase is detected.

Also, AILERON POSITION and CONTROL WHEEL POSITION should have changed

immediately before the ROLL increase. One may even note a variation in LATERAL

ACCELERATION.

Again, it should be emphasized that movement is indicated in the proper direction according to

the aircraft sign convention. Table 5-1 is provided as an aid in preparing a reasonableness

checklist. It summarizes parameters in a 34-parameter Digital Flight Data Recorder System that

may be expected to interact. A check mark (4) in a block indicates that the parameter

identified in the row and the parameter identified in the column are interdependent at some time

during takeoff and climb or approach and landing. Therefore, the movement of one parameter

should cause or be caused by movement in the other. The following examples show how to use

Table 5-1 in developing a reasonableness checklist for each parameter.

 a. Thrust Reverser Position Reasonableness and Quality Check. The column labeled Thrust

Reverser Position contains check marks in the rows labeled airspeed, engine thrust, longitudinal

acceleration, autopilot AFCS mode, and air/ground sensing. In preparing the checklist, one

would normally expect the thrust reverser to deploy during rollout after landing. Thus, the

following checklist might be developed using the parameters identified by a check mark.

 (1) Examine the thrust reverser in-transit and the thrust reverser deployed data to

determine that they indicate in-transit only for a short period during the landing roll and deployed

at the end of the in-transit period. The data should indicate in-transit and the deployed discrete

should go to zero or null near the end of the landing roll.

 (2) Examine the engine thrust data during the in-transit period and immediately after the

deployed indication. During the in-transit period, engine thrust should have decreased to near

zero and immediately after the deployed indication, the engine thrust should have increased to

near the maximum indication.
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APPENDIX 5. TYPICAL REASONABLENESS AND QUALITY CHECK

INSTRUCTIONS (CONTINUED)

 (3) Examine the airspeed and longitudinal thrust data. These two parameters should be

decreasing during the in-transit period and should dramatically decrease immediately after the

deployed indication.

 (4) Examine the autopilot AFCS mode discrete and the air/ground sensing discrete. The

autopilot AFCS mode discrete should indicate that the autopilot is disengaged and the

air/ground sensing switch discrete should indicate that the aircraft is on the ground.

 (5) Examine the remaining data for the thrust reverser discretes to ascertain that no intransit or deployed indications appear. If intermittent indications appear, determine that they are

within allowed values and do not have sufficient duration to be interpreted as an actual

deployment and that they would not obscure an actual deployment.

 b. Lateral Control Surface Position Reasonableness and Quality Check. The column

labeled lateral control surface position contains check marks in the rows labeled heading, roll

attitude, lateral control position, and localizer deviation. The lateral control surfaces are typically

ailerons that are used in establishing the aircraft in a turn and returning the aircraft to straight

flight from a turn. The lateral control surface position data may be checked along with the

lateral control position data. These checks may be accomplished during the approach and

landing segment.

 (1) Examine the lateral control surface position trace for deviations during the initial

approach segment. A large deviation would normally indicate the aircraft turning onto final

approach heading. Check that the lateral control position and roll attitude make a large change

at the same time.

 (2) Check to determine that heading begins to change immediately after the lateral control

surface position begins to change. Heading should continue to change after the lateral control

surface position returns to the zero or null value. The heading data should begin to change at a

lower rate when the lateral control surface position data moves in the opposite direction and

after the lateral control position is again returned to zero or null the heading data should again be

constant.

 (3) Check the localizer deviation for changes. Small lateral control surface position and

lateral control position data changes should accompany deviations from the localizer and returns

to the localizer.
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 (4) Check the lateral control surface position data to determine that there are no data

dropouts and that there is no noise in the data. If dropouts or noise are detected, determine that

they are within allowable values and that they would not be interpreted as an actual control

surface position movement.
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(CONTINUED)

TABLE 5-1 PARAMETER CORRELATION