What is required by the FARs before acting as pilot in command of an aircraft?

The requirement concerning blood alcohol levels before acting as pilot-in-command is established to ensure safety and mitigate the risks associated with impairment. According to the Federal Aviation Regulations (FARs), specifically 14 CFR Part 91.17, a pilot must have a blood alcohol concentration (BAC) of less than 0.04 percent to legally operate an aircraft. This regulation is enforced to ensure that pilots maintain a high level of alertness and cognitive function while flying, as alcohol consumption can significantly impair judgment and reaction times.

The limit of 0.04 percent is set as a standard threshold for aviation, reflecting a commitment to safe flying practices. While a pilot could potentially operate an aircraft with a BAC lower than this level, engaging in any alcohol consumption prior to flying is generally discouraged since it could still affect performance even below this threshold.

In this context, options that suggest a BAC higher than 0.04 percent do not comply with the FARs and therefore are not acceptable. Additionally, while having no alcohol is certainly a prudent approach to aviation safety, the FARs specifically outline the 0.04 percent BAC as the legal standard, which is why that option is the correct answer.