: If you are unsure of the source, use a checksum tool or an antivirus scanner. RAR files are commonly used for large data sets, but they can occasionally hide malicious scripts if downloaded from unverified repositories. Certification - Federal Aviation Administration
: Approval of the manufacturer's ability to duplicate that design consistently. DODIGV164.part21.rar
In technical and regulatory contexts, "Part 21" refers to a critical set of aviation standards. If your file is a digital copy of these regulations, here is an informative overview: : If you are unsure of the source,