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Appendix 2 to AMC 20-158A -- Generic transfer functions and attenuation

Available versions for ERULES-1963177438-19882

ED Decision 2022/001/R found in: AMC-20 Amdt 23 - Airworthiness of Products, Parts and Appliances (Jan 2022)

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Appendix 2 to
AMC 20-158A — Generic transfer functions and attenuation

ED Decision 2022/001/R

**1.         Generic transfer functions**

a.         Suitable transfer functions for
calculating the bulk current injection test levels for Level A display systems
(see Section 8(k)) are given in Figures A1-1 through A1-5. These are derived
generic transfer functions acquired from test results obtained from a
significant number of aircraft. The test results were processed to establish a
95 per cent population probability.

b.         The transfer functions are normalised
to a 1 V/m HIRF environment and may be multiplied linearly by the external
HIRF environment to establish the bulk current injection test level
requirements in the frequency range from 10 kHz up to 400 MHz. For example, if
the HIRF environment is 100 V/m at 3 MHz, then using Figure A1-1, multiply 0.7
mA/V/m by 100 V/m to establish a test level of 70 milliamperes (mA).

c.         Consult the User’s Guide (SAE ARP
5583A/EUROCAE ED-107A) for details on the use of generic transfer functions.

Figure A1-1: Generic transfer function —
Aeroplanes

![Aviation.Bot AI suggestion, not from EASA source: A log-log graph illustrating a generic transfer function for aeroplanes, depicting the bulk current injection test level in milliamperes per volt per meter (mA/V/m) as a function of frequency in megahertz (MHz).

Detailed Description:
The image displays a two-dimensional graph with a black grid, utilizing logarithmic scales for both its horizontal and vertical axes.
The horizontal axis, labeled "Frequency - MHz", ranges from 0.01 MHz to 1000 MHz, with major tick marks at 0.01, 0.1, 1, 10, 100, and 1000. Minor grid lines subdivide these major intervals logarithmically.
The vertical axis, labeled "mA/V/m", ranges from 0.001 mA/V/m to 1 mA/V/m, with major tick marks at 0.001, 0.01, 0.1, and 1. Minor grid lines subdivide these major intervals logarithmically.
A continuous red line, representing the generic transfer function, is plotted on this grid.
The red line begins at approximately (0.01 MHz, 0.006 mA/V/m) and exhibits the following segments:
1.  An upward sloping segment from approximately 0.01 MHz to 3 MHz, where the value increases from about 0.006 mA/V/m to 0.7 mA/V/m.
2.  A horizontal segment from 3 MHz to 15 MHz, where the value remains constant at 0.7 mA/V/m. This segment is explicitly marked by two labeled points: "3, 0.7" at the coordinate (3 MHz, 0.7 mA/V/m) and "15, 0.7" at the coordinate (15 MHz, 0.7 mA/V/m).
3.  A downward sloping segment from 15 MHz to 400 MHz, where the value decreases from 0.7 mA/V/m to 0.3 mA/V/m. This segment is explicitly marked by a labeled point "400, 0.3" at the coordinate (400 MHz, 0.3 mA/V/m).
The red line continues beyond 400 MHz, maintaining its downward slope.

Contextual Linkage: This graph provides the generic transfer function values, expressed in mA/V/m, which are used to determine bulk current injection test levels based on the frequency of the High-Intensity Radiated Field (HIRF) environment. The y-axis value (mA/V/m) represents the bulk current injection test level normalized to a 1 V/m HIRF environment, allowing for linear scaling with actual HIRF environment values. The labeled points define critical frequency and transfer function values that characterize the response curve.](file_tNNDI2wQkpg/image075.png)

Note: Generic transfer function
normalised to 1 V/m for an aircraft with a fuselage length of ≤ 25 m.

Figure A1-2: Generic transfer function —
Aeroplanes

![Aviation.Bot AI suggestion, not from EASA source: **Overall Summary:** The image displays a log-log plot of a generic transfer function, normalized to 1 V/m, for aeroplanes with a fuselage length greater than 25 meters and less than or equal to 50 meters, illustrating the relationship between frequency and bulk current injection test levels.

**Detailed Description:** The image presents a two-dimensional line graph with a black grid on a white background. Both the horizontal (x) and vertical (y) axes use a logarithmic scale.

The horizontal axis is labeled "Frequency - MHz" and ranges from 0.01 MHz to 1000 MHz. Major tick marks are present at 0.01, 0.1, 1, 10, 100, and 1000 MHz. Each decade is further subdivided by nine minor grid lines.

The vertical axis is labeled "mA/V/m" and ranges from 0.01 mA/V/m to 1 mA/V/m. Major tick marks are present at 0.01, 0.1, and 1 mA/V/m. Each decade is further subdivided by nine minor grid lines.

A single red line represents the generic transfer function. This line consists of three distinct linear segments on the log-log plot:
1.  The first segment originates from the bottom-left corner of the plotted area, specifically at the coordinates (0.01 MHz, 0.01 mA/V/m). It ascends diagonally to the point (1.5 MHz, 0.7 mA/V/m). This point is explicitly labeled "1.5, 0.7" above and to the right of the line.
2.  The second segment is horizontal, indicating a constant value. It extends from (1.5 MHz, 0.7 mA/V/m) to (6 MHz, 0.7 mA/V/m). The point (6 MHz, 0.7 mA/V/m) is explicitly labeled "6, 0.7" above and to the right of the line.
3.  The third segment descends diagonally from (6 MHz, 0.7 mA/V/m) to (400 MHz, 0.15 mA/V/m). This final point is explicitly labeled "400, 0.15" below and to the right of the line. The red line terminates at this point, while the horizontal axis extends to 1000 MHz.

The black grid lines form a dense mesh across the entire plotting area, corresponding to the logarithmic subdivisions of both axes.

**Contextual Linkage:** This graph visually defines the generic transfer function for aeroplanes with fuselage lengths between 25m and 50m. It provides specific coordinate pairs (1.5, 0.7), (6, 0.7), and (400, 0.15) that delineate the shape of the function, which is used to determine bulk current injection test levels based on frequency. The y-axis represents the transfer function value in milliamperes per volt per meter (mA/V/m), indicating the induced current per unit of external electric field strength, while the x-axis represents the frequency in megahertz (MHz).](file_tNNDI2wQkpg/image076.png)

Note: Generic transfer function normalised to 1 V/m for an aircraft with
a fuselage lengthof > 25 mand ≤ 50 m.

Figure A1-3: Generic transfer function —
Aeroplanes

![Aviation.Bot AI suggestion, not from EASA source: The image displays a log-log graph illustrating a generic transfer function for aeroplanes with a fuselage length greater than 50 meters, normalized to a 1 V/m High-Intensity Radiated Field (HIRF) environment.

Detailed Description:
The image presents a two-dimensional line graph plotted on a grid.
The horizontal axis (X-axis) is labeled "Frequency - MHz" and uses a logarithmic scale ranging from 0.01 MHz on the left to 1000 MHz on the right. Major tick marks are present at 0.01, 0.1, 1, 10, 100, and 1000 MHz, with finer logarithmic subdivisions between them.
The vertical axis (Y-axis) is labeled "mA/V/m" and also uses a logarithmic scale, ranging from 0.01 mA/V/m at the bottom to 10 mA/V/m at the top. Major tick marks are present at 0.01, 0.1, 1, and 10 mA/V/m, with finer logarithmic subdivisions.
A black grid overlays the entire plot area, corresponding to the major and minor tick marks of both logarithmic axes.

A prominent red line, representing the generic transfer function, is plotted across the grid. This line is composed of several linear segments on the log-log scale, with specific points labeled with their (Frequency, mA/V/m) coordinates:
1.  The curve originates from the bottom-left area of the graph, starting approximately at (0.01 MHz, 0.05 mA/V/m).
2.  It rises linearly to a point labeled "0.5, 2.5", indicating a value of 2.5 mA/V/m at 0.5 MHz.
3.  From this point, the curve remains constant at 2.5 mA/V/m, forming a horizontal plateau, until it reaches a point labeled "5, 2.5", indicating 2.5 mA/V/m at 5 MHz.
4.  Following the plateau, the curve descends linearly to a point labeled "50, 0.3", indicating a value of 0.3 mA/V/m at 50 MHz.
5.  The curve continues its linear descent from this point to a final labeled point "400, 0.15", indicating a value of 0.15 mA/V/m at 400 MHz.
6.  The red line then continues to decrease further, extending to the right edge of the visible plot area, ending at approximately (600 MHz, 0.1 mA/V/m).

Contextual Linkage:
This graph provides the generic transfer function values (in mA/V/m) as a function of frequency (in MHz). The Y-axis value represents the ratio of bulk current injection test level (in milliamperes) to the external HIRF environment electric field strength (in Volts per meter), assuming a normalization to 1 V/m. This function is specifically applicable for aeroplanes with a fuselage length exceeding 50 meters.](file_tNNDI2wQkpg/image077.png)

Note: Generic transfer function
normalised to 1 V/m for an aircraft with a fuselage length of > 50 m.

Figure A1-4: Generic transfer function — Rotorcraft

**![Aviation.Bot AI suggestion, not from EASA source: **Overall Summary:** The image displays a log-log graph illustrating a generic transfer function for rotorcraft, showing the relationship between frequency in MHz and the transfer function value in mA/V/m.

**Detailed Description:**
The image presents a two-dimensional graph with logarithmic scales on both axes, overlaid with a black grid.

* **Horizontal Axis (X-axis):** Labeled "Frequency - MHz", this axis represents frequency on a logarithmic scale ranging from 0.01 MHz to 1000 MHz. Major tick marks are present at 0.01, 0.1, 1, 10, 100, and 1000. Each major decade interval is further subdivided by nine minor grid lines.
* **Vertical Axis (Y-axis):** Labeled "mA/V/m", this axis represents the transfer function value on a logarithmic scale ranging from 0.01 mA/V/m to 10 mA/V/m. Major tick marks are present at 0.01, 0.1, 1, and 10. Each major decade interval is further subdivided by nine minor grid lines.
* **Grid:** A comprehensive black grid covers the entire plot area, formed by the intersection of horizontal and vertical lines corresponding to the major and minor tick marks of both axes.
* **Generic Transfer Function Curve:** A thick, solid red line plots the generic transfer function.
 * The curve originates near the bottom-left of the graph, approximately at (0.01 MHz, 0.025 mA/V/m).
 * It ascends diagonally from 0.01 MHz, reaching a peak value.
 * A labeled point "5, 1.5" indicates that at 5 MHz, the transfer function value is 1.5 mA/V/m. This point marks the end of the initial ascending segment.
 * From 5 MHz to 30 MHz, the curve is a horizontal line segment, indicating a constant transfer function value of 1.5 mA/V/m.
 * A labeled point "30, 1.5" indicates that at 30 MHz, the transfer function value remains 1.5 mA/V/m. This point marks the beginning of a descending segment.
 * From 30 MHz, the curve descends diagonally.
 * A labeled point "400, 0.5" indicates that at 400 MHz, the transfer function value is 0.5 mA/V/m. This point marks the end of the plotted curve.

**Contextual Linkage:**
The graph visually defines the generic transfer function for rotorcraft by plotting the transfer function value (in mA/V/m) as a function of frequency (in MHz). The red line and its labeled coordinates (5, 1.5), (30, 1.5), and (400, 0.5) explicitly define the shape and critical values of this function across the frequency range from 0.01 MHz to 400 MHz, allowing for the determination of the transfer function at any given frequency within this range.](file_tNNDI2wQkpg/image078.png)**

Note: Generic transfer function
normalised to 1 V/m for a rotorcraft.

Figure A1-5: Generic transfer function — All aircraft

![Aviation.Bot AI suggestion, not from EASA source: The image displays a log-log plot illustrating a generic transfer function for all aircraft, showing the relationship between frequency and the transfer function in milliamperes per Volt per meter (mA/V/m).

Detailed Description:
The image is a two-dimensional line graph plotted on a logarithmic scale for both axes, featuring a white background and a black grid.

The horizontal axis, labeled "Frequency - MHz", represents frequency in megahertz. It is a logarithmic scale ranging from 0.01 MHz to 1000 MHz. Major tick marks are labeled at 0.01, 0.1, 1, 10, 100, and 1000. Each major decade interval is subdivided by nine minor tick marks.

The vertical axis, labeled "mA/V/m", represents the transfer function in milliamperes per Volt per meter. It is a logarithmic scale ranging from 0.01 mA/V/m to 10 mA/V/m. Major tick marks are labeled at 0.01, 0.1, 1, and 10. Each major decade interval is subdivided by nine minor tick marks.

A prominent red line, representing the generic transfer function, is plotted across the grid. This line consists of five connected linear segments on the log-log plot, with specific points labeled with their (Frequency, mA/V/m) coordinates:
1.  The line originates at the leftmost edge of the graph at 0.01 MHz, with an approximate value of 0.035 mA/V/m.
2.  It rises linearly to the point labeled "0.5, 2.5", indicating 0.5 MHz and 2.5 mA/V/m.
3.  From "0.5, 2.5", it extends horizontally to the right to the point labeled "5, 2.5", maintaining a constant value of 2.5 mA/V/m.
4.  From "5, 2.5", it descends linearly to the point labeled "10, 1.5", indicating 10 MHz and 1.5 mA/V/m.
5.  From "10, 1.5", it extends horizontally to the right to the point labeled "30, 1.5", maintaining a constant value of 1.5 mA/V/m.
6.  From "30, 1.5", it descends linearly to the point labeled "400, 0.5", indicating 400 MHz and 0.5 mA/V/m.
The red line terminates at the point (400 MHz, 0.5 mA/V/m).

Contextual Linkage:
The graph visually represents a generic transfer function, showing how the bulk current injection test level (in mA/V/m) varies with frequency (in MHz) for all aircraft types. The plotted curve defines specific transfer function values at different frequencies, which can be used to determine test levels. For instance, the graph shows that between 0.5 MHz and 5 MHz, the transfer function is constant at 2.5 mA/V/m, and between 10 MHz and 30 MHz, it is constant at 1.5 mA/V/m. The labeled points highlight key frequency and transfer function value pairs that define the shape of the curve.](file_tNNDI2wQkpg/image079.png)

Note: Generic transfer function
normalised to 1 V/m for all aircraft.

2.         Generic
attenuation

a.         Figure A1-6 shows the generic
attenuation for frequencies from 100 MHz to 18 GHz that can be used for
determining the internal HIRF environment where the equipment and associated
wiring for Level A display systems (see Section 9(k)) are installed. This
internal HIRF environment provides the test level for the integrated system
radiated susceptibility laboratory test. The external HIRF environment should
be divided by the appropriate attenuation, in linear units, to determine the internal
HIRF environment. For example, 12 dB or a 4:1 attenuation means that the test
level is the applicable external HIRF environment electric field strength
reduced by a factor of 4.

b.         Guidance on the use of the generic
attenuation is given below:

1.         No attenuation. No attenuation credit can be used when the
Level A display equipment and the associated wiring are located in aircraft
areas with no HIRF shielding, such as areas with unprotected, non-conductive
composite structures, areas where there is no guarantee of structural bonding,
or other open areas where no shielding is provided. The applicant may choose
to use no attenuation for equipment that may be installed in a broad range of
aircraft areas.

2.         6 dB attenuation. This attenuation is appropriate when the
Level A display equipment and the associated wiring are located in aircraft
areas with minimal HIRF shielding, such as a cockpit in a non-conductive
composite fuselage with minimal additional shielding, or areas on the wing
leading or trailing edges, or in wheel wells.

3.         12 dB attenuation. This attenuation is appropriate when
the Level A display equipment and the associated wiring are located entirely
within aircraft areas with some HIRF shielding, in aircraft with a metal
fuselage or a composite fuselage with shielding effectiveness equivalent to
metal. Examples of such areas are avionics bays not enclosed by bulkheads,
cockpits, and areas near windows, access panels, and doors without EMI
gaskets. Current-carrying conductors in this area, such as hydraulic tubing,
control cables, wire bundles, and metal wire trays, are not all electrically
bonded to the bulkheads they pass through.

4.         20 dB attenuation. This attenuation is appropriate when
the Level A display equipment and the associated wiring are located entirely
within aircraft areas with moderate HIRF shielding, in aircraft with a metal
fuselage or a composite fuselage with shielding effectiveness equivalent to
metal. In addition, wire bundles passing through bulkheads in these areas have
shields electrically bonded to the bulkheads. Wire bundles are installed close
to metal structure and take advantage of other inherent shielding characteristics
provided by metal structure. Current-carrying conductors, such as hydraulic
tubing, cables, and metal wire trays are electrically bonded to all the
bulkheads they pass through.

5.         32 dB attenuation. This attenuation is appropriate when
the level A display equipment and all the associated wiring to and from
equipment are located entirely within areas with very effective HIRF shielding
to form an electromagnetic enclosure.

6.         Generic attenuation for rotorcraft. Display units
installed in rotorcraft typically have minimal attenuation unless specific
shielding is provided in the bulkhead, glare shield, panel, and doors.

c.         Different attenuation values may be
appropriate for different frequency ranges. For example, 0 dB attenuation may
be used for the frequency range of 100 to 400 MHz, 6 dB attenuation for the
frequency range of 400 MHz to 1 GHz, and 12 dB attenuation for the frequency
range of 1 to 18 GHz. If an applicant intends to use different attenuation
values for various frequency ranges, then they should also provide the
supporting rationale.

d.         Consult the User’s Guide (SAE ARP
5583A/EUROCAE ED-107A) for details on the use of generic attenuation.

**3.         Measured transfer functions or attenuation**

The applicant may produce their own generic transfer
functions and attenuation for their Level A display systems (see Section 9(k))
based on actual measurements on their aircraft models. These transfer
functions and the attenuation can then be used in their HIRF compliance
submission in place of the generic transfer functions and attenuation
specified in this Appendix. The Agency encourages this approach because it
provides a more accurate reflection of the true internal HIRF environment for
aircraft models. However, if an applicant intends to produce their own generic
transfer functions and attenuation, then this approach should also be
addressed in the HIRF compliance plan (see Section 6(a)) that is submitted to
the Agency for acceptance.

Figure A1-6: Generic attenuation values — All aircraft

100 MHz to 18 GHz

![Aviation.Bot AI suggestion, not from EASA source: This image is a 2D line graph illustrating five distinct generic attenuation values in decibels (dB) as a function of frequency in gigahertz (GHz), applicable for all aircraft.

Detailed Description:
The image displays a Cartesian coordinate system with a logarithmic X-axis and a linear Y-axis, forming a grid.
The X-axis is labeled "Frequency - GHz" and ranges from 0.1 GHz to 100 GHz, with major tick marks at 0.1, 1, 10, and 100. Minor tick marks subdivide each decade logarithmically.
The Y-axis is labeled "Attenuation (dB)" and ranges from 0 dB to 35 dB, with major tick marks at 0, 5, 10, 15, 20, 25, 30, and 35. Minor tick marks are present at 1 dB intervals.
A black grid overlays the graph, corresponding to both major and minor tick marks on both axes.

Five horizontal lines are plotted on the graph, each representing a constant attenuation value across the frequency range from 0.1 GHz to approximately 18 GHz. Each line is distinctly colored, styled, and marked, with a corresponding label on the right side of the plot:
1.  The topmost line is solid blue, marked with blue 'x' symbols at its start (0.1 GHz) and end (approximately 18 GHz). It is positioned at 32 dB on the Y-axis and labeled "32 dB".
2.  The second line from the top is red and dashed, marked with red 'x' symbols at its start (0.1 GHz) and end (approximately 18 GHz). It is positioned at 20 dB on the Y-axis and labeled "20 dB".
3.  The third line from the top is solid green, marked with green triangle symbols at its start (0.1 GHz) and end (approximately 18 GHz). It is positioned at 12 dB on the Y-axis and labeled "12 dB".
4.  The fourth line from the top is magenta and dash-dotted, marked with orange square symbols at its start (0.1 GHz) and end (approximately 18 GHz). It is positioned at 6 dB on the Y-axis and labeled "6 dB".
5.  The bottommost line is solid red, marked with red diamond symbols at its start (0.1 GHz) and end (approximately 18 GHz). It is positioned at 0 dB on the Y-axis and labeled "0 dB".

Contextual Linkage:
The graph visually presents five discrete, constant attenuation values (0 dB, 6 dB, 12 dB, 20 dB, and 32 dB) that are applicable across a broad frequency spectrum, specifically from 0.1 GHz (100 MHz) to approximately 18 GHz. Each horizontal line indicates that the specified attenuation value remains constant regardless of the frequency within this range.](file_tNNDI2wQkpg/image080.png)

[Amdt 20/23]