Can ATC override a crossing restriction on an approach plate?

A Reddit thread posing a question from a pilot flying the ILS RWY 09 approach into Kamloops, British Columbia (CYKA) highlights a scenario that working pilots encounter more often than checkride prep might suggest: an ATC-issued altitude that appears to conflict with a published crossing restriction on an approach plate. In this case, the pilot was inbound from the southeast to OVENA, a fix on the approach chart that carries a published restriction to cross at or above 8,100 feet. ATC, however, issued a clearance down to 8,000 feet. The pilot elected to remain above 8,100 feet out of caution but raised the reasonable question of whether descending to the ATC-assigned 8,000 feet would have been legal.

The underlying principle here is well established in both FAA and Transport Canada regulatory frameworks, and it comes down to the hierarchy between charted procedures and live ATC instructions. A published crossing restriction on an instrument approach procedure exists primarily for obstacle clearance and terrain separation, and in many cases also for traffic deconfliction with other procedures or airspace. When a pilot is cleared for an approach and has not yet been given an explicit instruction that supersedes the chart, the published altitudes on the plate govern. However, ATC retains the authority to issue altitude assignments that override charted restrictions, provided the controller's system accounts for the required separation from terrain and other traffic — which is precisely why radar vectoring and MVA/MOCA charts exist independently of the published procedure. The critical distinction is between an instruction like "descend and maintain 8,000, cross OVENA at or above 8,100 as published" versus an unambiguous "descend and maintain 8,000" issued without reference to the restriction, with the aircraft not yet cleared for the approach or being vectored off the charted transition. In Canada, as in the U.S., if ATC assigns an altitude that is explicitly lower than a charted crossing restriction and the pilot is not established on a segment of the approach where the restriction is mandatory (i.e., not yet "cleared for the approach" past that fix), the ATC assignment can legally supersede the chart, because the controller is using radar monitoring to ensure obstacle and traffic separation instead of relying on the procedure's built-in protections.

This matters significantly to professional pilots because misjudging this hierarchy in either direction creates operational risk. Descending below a charted restriction without a clear, unambiguous ATC instruction that specifically authorizes it can result in a controlled flight into terrain risk in mountainous terrain, and Kamloops sits in a valley environment where obstacle clearance margins are not generous — exactly the kind of setting where crossing restrictions are published for a reason. Conversely, refusing a valid ATC descent clearance based on a mistaken belief that the chart always wins can create unnecessary traffic conflicts, spacing problems, or missed approach sequencing that controllers are actively trying to manage. The pilot's decision in this scenario to query or remain conservative by staying above 8,100 feet was the operationally sound choice when clarity was lacking — when in doubt, query ATC directly ("confirm you want us below the OVENA crossing restriction") rather than assume either interpretation. This is standard CRM and ATC-communication practice taught in both airline and business aviation training: ambiguous clearances near terrain-sensitive fixes should always be verbally confirmed rather than silently complied with or silently overridden.

More broadly, this incident reflects a recurring theme in mountain and valley airport operations across Canada and the western U.S., where controllers, particularly in non-radar or limited-radar environments, may not always explicitly reference charted restrictions when issuing altitudes, especially during busy periods or when using standard phraseology shortcuts. It also underscores the value of pilots maintaining a strong working knowledge of local MVA/MEA structures and understanding that ATC's radar-derived separation authority, while real, is not a blanket license to ignore published obstacle protection without positive confirmation. For operators flying into terrain-challenged fields like Kamloops — a known factor for regional carriers, medevac operations, and business aviation serving the BC interior — this kind of altitude ambiguity is a useful reminder to brief crossing restrictions explicitly during approach briefings and to treat any ATC clearance that conflicts with a charted restriction as a cue for immediate clarification rather than default compliance.