Seattle center controllers reported an aircraft descended below the cleared altitude as well as the ...

Attributes
ACN	1465270
Time
Date	201707
Local Time Of Day	1801-2400
Place
Locale Reference	ZSE.ARTCC
State Reference	WA
Environment
Light	Dusk
Aircraft 1
Make Model Name	Dash 8-400
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Other / Unknown
Qualification	Air Traffic Control Developmental
Person 2
Function	Enroute
Qualification	Air Traffic Control Developmental
Events
Anomaly	ATC Issue All Types Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT

Narrative:

There were aircraft sequenced near glacier peak and the r-side told the front one; the one that descended below the mia (minimum IFR altitude); to fly a heading and descend and maintain 13000 ft. The read back was covered by our paired freq and the r-side said something along the lines of 'read back blocked; try again'. I don't recall what the pilot read back but he must have missed the altitude because he made the turn and descended below the glacier peak mia. The r-side immediately issued a low altitude alert once we saw the MSAW (minimum safe altitude warning) flashing and the aircraft climbed to 13000 ft.I should have suggested to split the sector earlier because we had a few instances of the paired frequencies stepping on each other.

Original NASA ASRS Text

Title: Seattle Center Controllers reported an aircraft descended below the cleared altitude as well as the Minimum IFR Altitude.

Narrative: There were aircraft sequenced near Glacier Peak and the R-side told the front one; the one that descended below the MIA (Minimum IFR Altitude); to fly a heading and descend and maintain 13000 ft. The read back was covered by our paired freq and the R-side said something along the lines of 'read back blocked; try again'. I don't recall what the pilot read back but he must have missed the altitude because he made the turn and descended below the Glacier Peak MIA. The R-side immediately issued a low altitude alert once we saw the MSAW (Minimum Safe Altitude Warning) flashing and the aircraft climbed to 13000 ft.I should have suggested to split the sector earlier because we had a few instances of the paired frequencies stepping on each other.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Seattle center controllers reported an aircraft descended below the cleared altitude as well as the minimum IFR altitude.