14 CFR Part 25eCFR Sep 29, 2026
Appendix L to Part 25
HIRF Environments and Equipment HIRF Test Levels
This appendix specifies the HIRF environments and equipment HIRF test levels for electrical and electronic systems under § 25.1317. The field strength values for the HIRF environments and equipment HIRF test levels are expressed in root-mean-square units measured during the peak of the modulation cycle.
HIRF environment I is specified in the following table:
Table I.—HIRF Environment I
| Frequency | Field strength (volts/meter) | |
|---|---|---|
| Peak | Average | |
| 10 kHz-2 MHz | 50 | 50 |
| 2 MHz-30 MHz | 100 | 100 |
| 30 MHz-100 MHz | 50 | 50 |
| 100 MHz-400 MHz | 100 | 100 |
| 400 MHz-700 MHz | 700 | 50 |
| 700 MHz-1 GHz | 700 | 100 |
| 1 GHz-2 GHz | 2,000 | 200 |
| 2 GHz-6 GHz | 3,000 | 200 |
| 6 GHz-8 GHz | 1,000 | 200 |
| 8 GHz-12 GHz | 3,000 | 300 |
| 12 GHz-18 GHz | 2,000 | 200 |
| 18 GHz-40 GHz | 600 | 200 |
In this table, the higher field strength applies at the frequency band edges.
HIRF environment II is specified in the following table:
Table II.-HIRF Environment II
| Frequency | Field strength (volts/meter) | |
|---|---|---|
| Peak | Average | |
| 10 kHz-500 kHz | 20 | 20 |
| 500 kHz-2 MHz | 30 | 30 |
| 2 MHz-30 MHz | 100 | 100 |
| 30 MHz-100 MHz | 10 | 10 |
| 100 MHz-200 MHz | 30 | 10 |
| 200 MHz-400 MHz | 10 | 10 |
| 400 MHz-1 GHz | 700 | 40 |
| 1 GHz-2 GHz | 1,300 | 160 |
| 2 GHz-4 GHz | 3,000 | 120 |
| 4 GHz-6 GHz | 3,000 | 160 |
| 6 GHz-8 GHz | 400 | 170 |
| 8 GHz-12 GHz | 1,230 | 230 |
| 12 GHz-18 GHz | 730 | 190 |
| 18 GHz-40 GHz | 600 | 150 |
In this table, the higher field strength applies at the frequency band edges.
Equipment HIRF Test Level 1. (1) From 10 kilohertz (kHz) to 400 megahertz (MHz), use conducted susceptibility tests with continuous wave (CW) and 1 kHz square wave modulation with 90 percent depth or greater. The conducted susceptibility current must start at a minimum of 0.6 milliamperes (mA) at 10 kHz, increasing 20 decibels (dB) per frequency decade to a minimum of 30 mA at 500 kHz.
From 500 kHz to 40 MHz, the conducted susceptibility current must be at least 30 mA.
From 40 MHz to 400 MHz, use conducted susceptibility tests, starting at a minimum of 30 mA at 40 MHz, decreasing 20 dB per frequency decade to a minimum of 3 mA at 400 MHz.
From 100 MHz to 400 MHz, use radiated susceptibility tests at a minimum of 20 volts per meter (V/m) peak with CW and 1 kHz square wave modulation with 90 percent depth or greater.
From 400 MHz to 8 gigahertz (GHz), use radiated susceptibility tests at a minimum of 150 V/m peak with pulse modulation of 4 percent duty cycle with a 1 kHz pulse repetition frequency. This signal must be switched on and off at a rate of 1 Hz with a duty cycle of 50 percent.
Equipment HIRF Test Level 2. Equipment HIRF test level 2 is HIRF environment II in table II of this appendix reduced by acceptable aircraft transfer function and attenuation curves. Testing must cover the frequency band of 10 kHz to 8 GHz.
Equipment HIRF Test Level 3. (1) From 10 kHz to 400 MHz, use conducted susceptibility tests, starting at a minimum of 0.15 mA at 10 kHz, increasing 20 dB per frequency decade to a minimum of 7.5 mA at 500 kHz.
From 500 kHz to 40 MHz, use conducted susceptibility tests at a minimum of 7.5 mA.
From 40 MHz to 400 MHz, use conducted susceptibility tests, starting at a minimum of 7.5 mA at 40 MHz, decreasing 20 dB per frequency decade to a minimum of 0.75 mA at 400 MHz.
From 100 MHz to 8 GHz, use radiated susceptibility tests at a minimum of 5 V/m.