A CFI's account of a failed Instrument Rating - Airplane (IRA) checkride has surfaced a recurring point of contention in flight instruction: how strictly examiners should interpret the FAA Airman Certification Standards (ACS) tolerances during evaluation. In this case, a student flying an RNAV approach to LNAV minimums leveled off 80 to 100 feet above the Minimum Descent Altitude (MDA) rather than descending fully to it. The check instructor issued a "notice of disapproval" (an unsat) specifically for that deviation, despite the instructing CFI noting the rest of the flight was otherwise passable. The instructing CFI's contention is straightforward: the Instrument ACS altitude tolerance on non-precision approaches is +100/-0 feet from the MDA, meaning an aircraft flown 80-100 feet above minimums is, by the letter of the standard, still within tolerance and should not by itself constitute a bust.
The disagreement highlights a persistent gray area in checkride administration—the difference between meeting a published numerical tolerance and demonstrating the judgment and precision an examiner wants to see. Descending to and maintaining MDA (rather than habitually leveling off well above it) is emphasized industry-wide because non-precision approaches often leave little margin between MDA and the missed approach point, and pilots who chronically level off high risk continuing a missed approach without ever having descended low enough to see the runway environment, even when conditions would technically permit landing. Many instructors, including the one in this account, teach a buffer (commonly 20-50 feet) above MDA to guard against inadvertently busting the floor, which is a widely accepted risk-management technique. But an evaluator can reasonably view an 80-100 foot buffer as excessive avoidance of the MDA rather than prudent margin, especially if it reflects an underlying discomfort with precise altitude control rather than deliberate technique. Examiners have latitude under the ACS to fail an applicant for demonstrating a lack of proficiency or poor judgment even when a specific numerical tolerance isn't technically breached, provided the disapproval is tied to the relevant Task and its associated skill elements.
For working pilots and instructors, this incident is a useful reminder that ACS tolerances represent outer limits, not target performance windows, and that examiners are trained to assess whether an applicant demonstrates command of the aircraft consistent with the standard's intent, not merely compliance with a number. In real-world IFR operations, particularly for Part 135 and Part 91 pilots flying into non-towered fields with LNAV-only minimums, the ability to fly a stabilized approach that reaches MDA promptly and holds it precisely is directly tied to approach success rates and go-around decision-making. A pilot who habitually stays high "for safety" may be masking marginal altitude control skills, and check airmen at any level—Part 141, Part 61, or an airline's training department—are generally trained to probe for that distinction. This is especially relevant as more single-pilot IFR operators, from flight-training environments up through corporate and fractional operations, rely on RNAV LNAV and LNAV/VNAV approaches as GPS overlays replace legacy VOR and NDB procedures, making precise, repeatable altitude discipline on non-precision approaches an increasingly foundational skill rather than a niche one.
More broadly, the thread reflects an ongoing tension in aviation training between codified standards and examiner discretion, a topic that recurs whenever a marginal or borderline performance results in disapproval. Flight schools and Part 141 programs in particular walk a fine line: the structured nature of a 141 curriculum invites students and instructors to treat ACS numbers as pass/fail thresholds, while DPEs and check airmen are ultimately evaluating whether the applicant is safe to exercise the certificate independently. For CFIs, the takeaway is less about relitigating this individual unsat and more about calibrating instructional technique so that students consistently fly to MDA with minimal margin, rather than building habits that, while technically compliant, could draw scrutiny on a checkride or, more importantly, degrade approach success and situational awareness in actual instrument conditions.