The identifier most commonly refers to a specific United States Federal Register document from 1995 or is part of broader regulatory guidance regarding the transport of hazardous materials. Option 1: Federal Register Document (1995)
Standards for FlexRay-based vehicle network systems. Download 21681 pdf
Airworthiness Standards; Flight Control System Details. The identifier most commonly refers to a specific
The official guide is available at IATA.org . Option 3: Other Technical Standards If neither of the above fits, "21681" might refer to: search for the specific agency (e.g.
If "21681" alone yields too many results, search for the specific agency (e.g., "FAA 21681 PDF"). Battery guidance document - IATA
You can find the official PDF through GovInfo or the Federal Register archive. Option 2: IATA Lithium Battery Guidance