Advisory
Circular
Subject: AVIATION DATABUS
ASSURANCE
Date: 08/04/06
Initiated by: AIR-100
AC No: 20-156
1. PURPOSE.
a. This advisory circular (AC) is for aircraft and aircraft engine manufacturers and
designers. We provide a means to gain Federal Aviation Administration (FAA) approval of your
aviation databus by showing the databus design performs its intended function and satisfies the
applicable airworthiness requirements when installed on an aircraft or aircraft engine.
b. This AC is not mandatory and does not constitute a regulation. This AC describes an
acceptable means, but is not the only means, to gain databus certification. However, if you use
the means described, you must follow it in all important respects.
2. MOTIVATION FOR GUIDANCE.
a. Aircraft, engine and avionics manufacturers want to take advantage of commercially
available databus technology that would reduce aircraft weight and development/manufacturing
time, and increase airborne system performance. This desire motivates manufacturers to
consider replacing point-to-point wiring and uni-directional databuses (for example, ARINC 429
databus) with faster and lighter bi-directional databuses. The guidance in this AC is intended for
new type certificate or major changes of aircraft installations with highly-integrated and complex
databus technology. It is not intended for systems with previously approved or legacy databus
technology unless the databus is used in a significant different way. You can use alternate
methods to ensure that the databus performs its intended function and meets airworthiness
requirements when installed on an aircraft or aircraft engine. Coordinate your plans for alternate
methods with us early in the certification project.
b. Databuses transfer information between line replaceable units (LRU) and line
replaceable modules or avionics modules installed in an aircraft. Aircraft and avionics
manufacturers propose to use different types of databuses on aircraft. These databuses are
becoming more complex as aircraft, aircraft engine, and avionics manufacturers integrate more
avionics components into the aircraft and aircraft engine data sources, requiring accommodations
for larger data transfers. System engineers have considerable flexibility when designing a
databus because there are many physical and logical configurations for airborne systems
architecture, data units or packets, protocols, message traffic, and so on, allowing avionics
manufacturers, databus vendors, and system integrators more latitude when configuring
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