___ II~------ ___ II~------ Appendix 2 Appendix 2. Definitions The following definitions apply to this AC:
TERM Attachment Point Continued Safe Flight and Landing Equipment External Environment
DEFINITION The level of transient voltage or current that appears at the equipment Actual Transient Level interface circuits because of the external environment. This level may be (ATL) less than or equal to the transient control level, but should not be greater.
Aperture An electromagnetically transparent opening.
A point where the lightning flash contacts the aircraft.
A condition in which transients permanently alter the electrical Component Damage characteristics of a circuit. Because of this, the component can no longer perform to its specifications.
The aircraft can safely abort or continue a takeoff, 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 transport airplanes, the pilot must be able to land safely at a suitable airport. For Part 23 airplanes, 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.
Physical damage to the aircraft or electrical and electronic systems.
Direct attachment of lightning to the system’s hardware or components Direct Effects causes the damage. Examples of direct effects include tearing, bending, burning, vaporization, or blasting of aircraft surfaces and structures, and damage to electrical and electronic systems.
Component of an electrical or electronic system with interconnecting electrical conductors.
Equipment Transient The peak amplitude of transients to which you qualify your equipment.
Design Level (ETDL) The natural lightning environment, outside the aircraft, for design and certification purposes. See AC 20-155, which references documents that provide additional guidance on aircraft lightning environment and related waveforms.
Electrical transients induced by lightning in aircraft electrical or electronic circuits.
Indirect Effects A2-1
II II Appendix 2
TERM DEFINITION 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 AC 20-155, 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 center.
A charge center 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 characterized 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 attaches to the aircraft. See AC 20-155.
flashes. The multiple bursts appear most intense when the initial leader Multiple Stroke Two or more lightning return strokes during a single lightning flash. See AC 20-155.
The maximum allowable level of transients that appear at the equipment Transient Control Level (TCL) interface circuits because of the defined external environment.
A2-2
Appendix 3 Appendix 3. Acronyms We use the following acronyms throughout this AC:
14 CFR Title 14 of the Code of Federal Regulations AC Advisory Circular ACO Aircraft Certification Office ARP Aerospace Recommended Practice ATL Actual Transient Level 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 A3-1