Appendix 1 to AMC 20-136 Definitions and acronyms

ED Decision 2015/017/R

a.       Definitions

Actual Transient Level (ATL): The level of transient voltage or current that appears at the equipment interface circuits because of the external environment. This level may be less than or equal to the transient control level, but should not be greater.

Aperture: An electromagnetically transparent opening.

Attachment point: A point where the lightning flash contacts the aircraft.

Component damage: A condition in which transients permanently alter the electrical characteristics of a circuit. Because of this, the component can no longer perform to its specifications.

Continued safe flight and landing: The aircraft can safely abort or continue a take-off, or continue controlled flight and landing, possibly using emergency procedures. The aircraft must do this without requiring exceptional pilot skill or strength. Some aircraft damage may occur because of the failure condition or on landing. For large 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.

Direct effects: Physical damage to the aircraft or electrical and electronic systems. Direct attachment of lightning to the system’s hardware or components causes the damage. Examples of direct effects include tearing, bending, burning, vaporisation, or blasting of aircraft surfaces and structures, and damage to electrical and electronic systems.

Equipment Component of an electrical or electronic system with interconnecting electrical conductors.

Equipment Transient Design Level (ETDL): The peak amplitude of transients to which equipment is qualified.

External environment: The natural lightning environment, outside the aircraft, for design and certification purposes. See EUROCAE ED-84A, which reference documents that provide additional guidance on aircraft lightning environment and related waveforms.

Indirect effects: Electrical transients induced by lightning in aircraft electrical or electronic circuits.

Internal environment: The potential fields and structural voltages inside the aircraft produced by the external environment.

Lightning flash: The total lightning event. It may occur in a cloud, among clouds, or between a cloud and the ground. It can consist of one or more return strokes, plus intermediate or continuing currents.

Lightning strike: Attachment of the lightning flash to the aircraft.

Lightning strike zones: Aircraft surface areas and structures that are susceptible to lightning attachment, dwell time, and current conduction. See EUROCAE ED-91, which references documents that provide additional guidance on aircraft lightning zoning.

Lightning stroke (return stroke): A lightning current surge that occurs when the lightning leader (the initial current charge) makes contact with the ground or another charge centre. A charge centre is an area of high potential of opposite charge.

Margin: The difference between the equipment transient design levels and the actual transient level.

Multiple burst: A randomly spaced series of bursts of short duration, low amplitude current pulses, with each pulse characterised by rapidly changing currents. These bursts may result as the lightning leader progresses or branches, and are associated with the cloud-to-cloud and intra-cloud flashes. The multiple bursts appear most intense when the initial leader attaches to the aircraft. See EUROCAE ED-84A.

Multiple stroke: Two or more lightning return strokes during a single lightning flash. See EUROCAE ED-84A.

Transient Control Level (TCL): The maximum allowable level of transients that appear at the equipment interface circuits because of the defined external environment.

b.      Acronyms

AC:              Advisory Circular

AMC:           Acceptable Means of Compliance

ARP:            Aerospace Recommended Practice

ATL:            Actual Transient Level

CS:              Certification Specification

ETDL:          Equipment Transient Design Level

EASA:          European Aviation Safety Agency

EUROCAE:   European Organization for Civil Aviation Equipment

FAA:            Federal Aviation Administration

ICA:             Instructions for Continued Airworthiness

TCL:             Transient Control Level

[Amdt 20/13]