The question of whether endorsement A.39 is required alongside A.1 and A.78 for a commercial multiengine add-on rating touches a genuinely ambiguous area of FAA regulatory guidance that routinely surfaces among certificated flight instructors preparing applicants for practical tests under 14 CFR §61.63. The scenario involves a pilot who already holds a commercial certificate and is adding a multiengine class rating — a process governed not by the full commercial certificate requirements of §61.125 and §61.127, but by the narrower additional-rating pathway of §61.63(c). The endorsement structure specified in AC 61-65 (currently AC 61-65J) is designed to track these distinctions, but the overlapping applicability of certain endorsements creates legitimate interpretive uncertainty for instructors and applicants alike.
The core regulatory tension arises because the practical test for a commercial multiengine add-on is administered to commercial pilot standards — meaning the Airman Certification Standards for commercial multiengine land apply — even though the applicant is not pursuing an original commercial certificate. Endorsement A.78, which satisfies §61.63, certifies that the applicant has received the required training for an additional aircraft category or class rating. Endorsement A.1 serves as the standard practical test readiness endorsement, confirming the applicant has received instruction in the applicable areas of operation and is prepared for the test. Endorsement A.39, by contrast, is specifically keyed to the commercial pilot practical test under §61.129, attesting that the applicant has met the aeronautical experience requirements and is ready for a commercial certificate practical. Because the add-on applicant is not being issued a new certificate — only an additional class rating — A.39's direct regulatory hook to §61.129 arguably does not apply in the same manner. Nonetheless, many DPEs and FAA Flight Standards District Offices have taken the position that because the test is being conducted at the commercial level, the commercial-level readiness endorsement provides important substantive documentation and should be included as a matter of best practice, if not strict regulatory mandate.
For working CFIs, this distinction carries real professional consequence. An endorsement package presented to a DPE that is incomplete or incorrectly scoped can result in a practical test being terminated before it begins, a logbook correction requirement, or — in cases where pattern of deficiency is identified — scrutiny of the instructor's broader endorsement practices during surveillance or certificate action proceedings. The FAA has made endorsement accuracy an increasing area of emphasis in recent years, partly driven by data showing that errors in logbook endorsements and eligibility documentation are among the most common discrepancies found during IACRA and logbook reviews at practical tests. CFIs operating under Part 141 schools face additional oversight through chief instructor review processes, but Part 61 independent instructors bear sole responsibility for endorsement accuracy without that institutional backstop.
The broader relevance for aviation operators — particularly those managing pilot training pipelines in Part 135, Part 91K, or business aviation environments — is that add-on ratings are a standard tool for transitioning single-engine commercial pilots into multiengine turbine equipment. A pilot whose commercial multiengine add-on was endorsed incorrectly, and whose practical test was nonetheless completed, may carry a certificate action risk years later if a records audit surfaces the deficiency. Operators conducting their own certificate verification during hiring or during Part 135 check airman qualification reviews have an interest in understanding that the endorsement chain for add-on ratings is not identical to that for original certificates, and that minor but legally material differences in the applicable regulatory sections can affect the validity of the underlying certification. While FAA enforcement over technical endorsement errors in otherwise competent pilots is uncommon, the regulatory exposure is real and the question posed reflects exactly the kind of nuanced compliance awareness that distinguishes a careful instructor from one who treats endorsements as administrative afterthoughts.