Date: 201702
Local time of day: 0601-1200
Location: BOI.TRACON, ID
Flight conditions: Marginal
Weather elements / visibility: Turbulence
Light: Night
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class C BOI
ATC / advisory: TRACON BOI; Tower BOI
Reporter organization: Government
Reporter function: Approach; Departure; Flight Data / Clearance Delivery; Ground; Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Distraction; Workload; Situational Awareness
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Weather / Turbulence
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Contributing factors: Airspace Structure; Chart Or Publication; Procedure; Weather
Primary problem: Procedure

Narrative: I was working alone in the tower cab; all combined tower and approach positions; at the beginning of a midshift. Weather had been moving through the area with gusty winds and precipitation in the area. I had one other aircraft on approach on another frequency. First in sequence Aircraft X checked on descending via the SADYL and immediately reported moderate turbulence. The radar depicted that weather may be better with a slight vector to the west; and such a vector would also provide the appropriate sequence to make Aircraft X follow the first aircraft.I issued a clearance to the fix JIMMI as a vector for sequence; with a descent to 9000 feet. The instruction was read back correctly and I observed Aircraft X turn left toward the fix and continued descending. I obtained some additional information from Aircraft X concerning the turbulence. At that point I went to the computer in the back of the room and logged on to the AISR website to enter a PIREP for the moderate turbulence. After successfully logging on; no more than 30 seconds; I walked back to the radar scope and observed Aircraft X descending through 8000 feet. I instructed them to climb to 9000 feet. The pilot replied they were descending to 6000 feet. I again instructed them to climb to 9000 feet and informed them that they were in a 9000 foot Minimum Vectoring Altitude Area (MVA). They began climbing and reached around 8400 feet before they crossed into a 7000 foot MVA. The 6000 altitude is the final altitude on the arrival; and I suspect they missed entering the new altitude into the FMS. A minute later they apologized for missing the altitude and said that it was due to workload in the cockpit as a result of the moderate turbulence. They landed without incident and I issued a BRASHER warning after they landed and informed them that I would need to file the associated paperwork. The responsibility to enter the PIREP into AISR instead of transmitting it verbally to FSS resulted in my being away from the radar scope as the aircraft descended through their assigned altitude. I also did not use the 'Low Altitude Alert' phraseology; but instead immediately issued the correct assigned altitude; as it felt quicker to avoid continued descent and it was the natural muscle-memory altitude instruction. In hindsight; the 'Low Altitude Alert' phraseology may have resulted in the pilots not questioning the new altitude and beginning a climb sooner.Return the responsibility of computer based PIREP entry to FSS to allow controllers and to focus on the operation.




Synopsis: A Controller working alone on a mid shift reported leaving their radar position to enter a PIREP in to a computer and did not notice an aircraft descending below its assigned altitude below the Minimum Vectoring Altitude.