Appendix 1 to AMC 20-158A — Definitions and acronyms

1.         Definitions

Adverse effect: a response of a system that results in an unexpected and unacceptable operation of an aircraft system, or unexpected and unacceptable operation of the function performed by the system.

Attenuation: the term used to denote a decrease in the electromagnetic field strength in the transmission from one point to another. Attenuation may be expressed as a scalar ratio of the input magnitude to the output magnitude, or in decibels (dB).

Automatically recover: areturn to normal operations without pilot action.

Bulk current injection: amethod of electromagnetic interference (EMI) testing that involves injecting current into wire bundles through a current injection probe.

Channel:a subset of a system consisting of equipment, components, and interconnections, which performs an aircraft function provided by the system. A system could be composed of redundant similar or dissimilar channels in order to maintain the function at the aircraft level in case of failure on one or several channels.

Continued safe flight and landing: thecapability for continued controlled flight and landing at a suitable location, possibly using emergency procedures, but without requiring exceptional piloting skill or strength. For CS-25 aeroplanes, the pilot must be able to land safely at a suitable airport. For CS-23 aeroplanes, it is not necessary to land at an airport. For rotorcraft, the rotorcraft must continue to cope with adverse operating conditions, and the pilot must be able to land safely at a suitable site. Some aircraft damage may be associated with a failure condition during flight or upon landing.

Continuous wave: anRF signal consisting of only the fundamental frequency with no modulation in amplitude, frequency, or phase.

Coupling: theprocess whereby electromagnetic energy is induced in a system by radiation produced by an RF source.

Current injection probe: aninductive device designed to inject RF signals directly into wire bundles when clamped around them.

Direct drive test: anelectromagnetic interference (EMI) test that involves electrically connecting a signal source directly to the unit to be tested.

Electrical and electronic system: an electrical or electronic system includes all the electrical and electronic equipment, components, elements and the electrical interconnections that are required to perform a particular function.

Equipment: acomponent of an electrical or electronic system with interconnecting electrical conductors.

Equipment electrical interface: alocation on a piece of equipment where an electrical connection is made to the other equipment in a system of which it is a part. The electrical interface may consist of individual wires or wire bundles that connect the equipment.

External HIRF environment: electromagnetic RF fields at the exterior of an aircraft.

Field strength: themagnitude of the electromagnetic energy propagating in free space expressed in volts per metre (V/m).

Function:the specific action of a system, equipment, and flight crew performance aboard the aircraft that, by itself, provides a completely recognisable operational capability. For example, ‘display aircraft heading to the pilots’ is a function. One or more systems may perform a specific function, or one system may perform multiple functions.

HIRF environment: theelectromagnetic environment created by the transmission of high-power RF energy into free space.

HIRF vulnerability: thesusceptibility characteristics of a system that cause it to suffer adverse effects when performing its intended function as a result of having been subjected to a HIRF environment.

Immunity: thecapacity of a system or piece of equipment to continue to perform its intended function, in an acceptable manner, in the presence of RF fields.

Interface circuit: an electrical or electronic device connecting the electrical inputs and outputs of a piece of equipment to other pieces of equipment or devices in an aircraft.

Internal HIRF environment: the RF environment inside an airframe, equipment enclosure, or cavity. The internal RF environment is described in terms of the internal RF field strength or wire bundle current.

Margin: thedifference between the equipment susceptibility or qualification levels and the aircraft internal HIRF environment. Margin requirements may be specified to account for uncertainties in design, analysis, or test.

Modulation: the process whereby certain characteristics of a wave, often called the carrier wave, are varied in accordance with an applied function.

Non-normal situation: any situation that requires non-normal, abnormal, emergency, unusual procedures, or configurations for operating an aircraft.

Normal operation: a status where the system performs its intended function. When addressing compliance with CS23.1308(a)(2), 25.1317(a)(2), 27.1317(a)(2), and 29.1317(a)(2), the function whose failure would prevent the continued safe flight and landing should be in the same undisturbed state as before exposure to the HIRF threat, while other functions, performed by the same system, subject to CS23.1308(b) and (c), 25.1317(b) and (c), 27.1317(b) and (c), and 29.1317(b) and (c), are not required to be recovered. The system that performs the function may be nevertheless in a different state as long as the function is not adversely affected.

Radio frequency (RF): a frequency useful for radio transmission. The present practical limits of RF transmissions are roughly 10 kilohertz (kHz) to 100 gigahertz (GHz). Within this frequency range, electromagnetic energy may be detected and amplified as an electric current at the wave frequency.

Reflection plane: aconducting plate that reflects RF signals.

Similarity: theprocess of using existing HIRF compliance documentation and data from a system or an aircraft to demonstrate HIRF compliance for a nearly identical system or aircraft of equivalent design, construction, and installation.

Susceptibility: aproperty of a piece of equipment that describes its inability to function acceptably when subjected to unwanted electromagnetic energy.

Susceptibility level: thelevel where the effects of interference from electromagnetic energy become apparent.

Transfer function: theratio of the electrical output of a system to the electrical input of a system, expressed in the frequency domain. For HIRF, a typical transfer function is the ratio of the current on a wire bundle to the external HIRF field strength, as a function offrequency.

Timely manner: timely recovery has been introduced to account for the necessary period for complex systems to reconfigure safely after a disruption.The meaning of ‘in a timely manner’ therefore depends upon the function performed by the system to be evaluated, the specific system design, the interactions between that system and other systems, and interactions between the system and the flight crew. The definition of ‘in a timely manner’ must be determined for each specific system and for the specific functions performed by the system. The applicable definition could be included in the HIRF compliance plan for review and concurred with the Agency.

Upset: animpairment, either permanent or momentary, of the system operation. For example, a change of digital or analogue state that may or may not require a manualreset.

User’s Guide: thisrefers to SAE Document ARP 5583A or EUROCAE Document ED-107A.

2.         Acronyms

[Amdt 20/23]