The Federal Aviation Regulations draw a well-established but frequently misunderstood distinction between *acting* as pilot-in-command and *logging* pilot-in-command flight time, and this distinction sits at the heart of the question the Reddit post raises about the Herman Letter. Under 14 CFR 91.3, the acting PIC bears ultimate authority and responsibility for the operation of the aircraft, including all command decisions. Separately, under 14 CFR 61.51(e)(1)(i), any certificated pilot may log PIC time whenever that pilot is the sole manipulator of the controls of an aircraft for which the pilot holds the appropriate category and class rating. These are two distinct legal concepts triggered by different regulatory provisions, and the FAA's Office of Chief Counsel has issued legal interpretation letters — including the one colloquially known as the Herman Letter — to address exactly these kinds of ambiguities when both a qualified acting PIC and a less-qualified sole manipulator are aboard the same aircraft simultaneously.
The specific question regarding tailwheel aircraft turns on the nature of the 61.31(i) endorsement requirement. That endorsement is a prerequisite to *acting as PIC* of a tailwheel airplane, but it is not a category or class rating in the regulatory sense. Because 61.51(e)(1) ties PIC logging privileges to being "rated" for the aircraft — generally understood to mean holding the relevant category and class rating, not every applicable endorsement — the argument advanced in the post has regulatory support: a pilot holding a private certificate or higher, rated for single-engine land operations, may plausibly log PIC time as sole manipulator of a tailwheel Cub even absent the 61.31(i) endorsement, provided a properly endorsed or rated pilot is simultaneously acting as PIC and retaining full command authority. The acting PIC in that scenario is legally responsible for the flight and all decisions; the sole manipulator is simply entitled to credit for the stick time under the logging rules.
For working pilots, this distinction has practical relevance well beyond the tailwheel scenario. The same framework applies when an airline pilot under an IOE check ride manipulates the controls while the check airman acts as PIC, when a Part 135 SIC logs PIC time as sole manipulator on routes where the certificate holder does not require a type rating for the SIC seat, or when a pilot proficiency-flying an aircraft type for which they hold a rating but lack currency sits at the controls while a qualified captain holds command authority. In each case, two pilots can simultaneously be logging PIC time — one as acting PIC under 91.3, one as sole manipulator under 61.51 — without either entry being erroneous. Understanding that the logbook entry and the command designation are governed by separate regulatory subsections is foundational knowledge for any pilot managing complex flight department operations or multi-crew environments.
The broader significance of FAA legal interpretation letters like the Herman Letter is that they carry genuine regulatory weight even though they are not codified rules. Chief Counsel interpretations represent the agency's official legal position on how existing regulations apply to specific fact patterns, and courts have generally afforded them deference. For Part 91K, Part 135, and airline operators, these letters often resolve ambiguities that the underlying regulations do not address explicitly, and they can directly affect how training programs, currency tracking, and logbook policies are structured. Aviation legal counsel and chief pilots at larger flight departments routinely maintain libraries of relevant interpretations — covering everything from currency rules to crew pairing requirements — precisely because the gap between what the FARs say on their face and how the FAA interprets them in practice can have significant operational and certificate consequences. Pilots operating in complex regulatory environments are well served by treating these letters as primary regulatory research tools rather than secondary commentary.