Federal Aviation Regulation 14 CFR 61.31(g) requires any pilot acting as PIC of a pressurized aircraft with a service ceiling or maximum operating altitude above 25,000 feet MSL to hold a logbook endorsement from an authorized instructor certifying completion of specific ground and flight training elements. Those elements include the physiological aspects of high-altitude flight — hypoxia recognition, time of useful consciousness, gas expansion and bubble formation, decompression sickness — along with high-altitude aerodynamics, pressurization system operation, oxygen equipment, emergency descent procedures, and pitot-static system failures. The endorsement requirement exists specifically within Part 61 and governs Part 91 operations; it is separate from, and not automatically replaced by, type rating requirements or airline-specific training programs, which is the source of the confusion described in the Reddit post.
The specific exception at 61.31(g)(3)(iv) addresses pilots who received the training required under 61.31(g)(1) through an approved training program conducted under Part 121, 125, or 135. The provision holds that such pilots are not additionally required to obtain a separate Part 61 logbook endorsement from an independent instructor — provided the training was actually delivered and documented within that approved program. This is the crux of the interpretive problem: Part 121 type rating and PIC qualification programs are comprehensive and almost certainly cover every substantive element 61.31(g)(1) enumerates, but they do so within the operator's own approved training program records, not in a pilot's personal logbook in the form of an explicit high-altitude endorsement. The documentation lives in the carrier's training records, not in the format a Part 61 examiner or ramp inspector would expect to see.
For pilots who completed PIC qualification in a pressurized aircraft through a Part 121 operator and now wish to operate that same category of aircraft under Part 91 — common among airline pilots who own or fly fractional, charter, or corporate aircraft on the side — the practical risk is a documentation gap rather than a training gap. The training almost certainly occurred and satisfies the regulatory intent of 61.31(g). However, if the pilot cannot produce records showing that a Part 121 approved training program delivered those specific high-altitude training elements, compliance with the 61.31(g)(3)(iv) exception becomes difficult to demonstrate in the field. FAA legal interpretations have historically taken the position that the training record from the Part 121 operator can substitute for the logbook endorsement, but accessing those records after leaving a carrier, particularly years later, is not always straightforward.
The practical guidance in the professional pilot community — supported by guidance from aviation legal counsel and some FSDO interpretations — is to retain copies of all Part 121 training records documenting high-altitude ground and flight training completion, ideally including the specific curriculum outline from the operator's approved training program. If those records are unavailable or incomplete, obtaining a logbook endorsement from a CFI or ATP who can administer the required training elements under 61.31(g)(1) is both inexpensive and definitively closes the compliance gap. The endorsement itself requires no practical test, just documented ground and flight instruction. For pilots moving from the airline world into Part 91 or Part 135 charter operations in high-altitude pressurized aircraft, resolving this paperwork ambiguity proactively is far preferable to addressing it during a ramp check or after an incident.
This regulatory ambiguity reflects a broader structural friction in U.S. aviation rulemaking: Part 121's highly structured, operator-based training ecosystem does not map cleanly onto the individual pilot certificate and endorsement framework of Part 61, which governs Part 91 operations. As more airline-experienced pilots enter business aviation, whether through fractional programs, Part 135 operations, or direct Part 91 corporate roles, questions like this one are becoming more frequent. The FAA has addressed some of these crossover issues through legal interpretations and rulemaking, but 61.31(g) remains an area where a pilot's actual competency and their documented regulatory compliance can diverge in ways that create legal exposure without any corresponding safety concern.