Date: 202104
Local time of day: 0601-1200
Location: ZSE.ARTCC, WA
Aircraft: Medium Transport
Operator: Corporate
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach; Descent
Airspace: Class E ZSE
ATC / advisory: Center ZSE
Reporter organization: Government
Reporter function: Enroute; Handoff / Assist
Reporter qualification: Air Traffic Control Developmental
Human factors: Distraction; Situational Awareness; Workload
Anomaly: ATC Issue All Types; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Chart Or Publication; Human Factors; Procedure; Airspace Structure
Primary problem: Procedure

Narrative: Aircraft requested an RNAV Approach. The Radar Controller cleared the aircraft direct to the Initial Approach Fix. The route was updated in the computer to reflect. Aircraft was level at 13;000 feet and told to cross the Initial Approach Fix at 13;000 [ft.]; cleared RNAV Approach. I was talking with the Radar Controller immediately before saying this was a common error point where aircraft descend below the 12;100 [ft.] MEA (Minimum Enroute Altitude) to the intermediate fix. We observed the aircraft cross the Initial Approach Fix and begin descending. The Radar Controller drew a circle around the next fix for reference. When I came back around on my scan I observed the aircraft already below the MEA of 12;100 feet. I do not recall the exact altitude but it was below 12;000 feet. I brought this to the attention of the Radar Controller. Immediately they transmitted 'Aircraft X WHAT ARE YOU DOING?...' The Radar Controller told the airplane they were below the 12;100 [ft.] MEA. The pilot immediately asked for a visual approach and the Radar Controller asked if they had the field in sight. Upon the affirmative response; the visual approach clearance was issued. I inbounded the aircraft to the Tower and a brasher statement was issued. A low altitude safety alert was never issued.First action should have been to issue a low altitude alert and verify they have surrounding terrain in sight. This approach has had multiple MEA violations and we have been briefed that issuing safety alerts is utmost priority. I should have told the Radar Controller to issue the alert but they responded quickly to the aircraft asking 'what are you doing?' and got them cleared for a visual approach. Perhaps the placement of the MEA step downs is not as apparent as required on the approach plate. The other transitions have both caused issues before on this approach.




Synopsis: ZSE Center Controller working the Assist position reported an aircraft cleared for an approach descended below the published Minimum Enroute Altitude but was not issued a low altitude alert by the Radar Controller. The reporter stated it is a common occurrence for aircraft flying this procedure to descend below the published minima.