Date: 201812
Local time of day: 0001-0600
Location: ZZZ.ARTCC, US
Aircraft: PC-12
Operating under: Part 91
Flight plan: IFR
Flight phase: Climb
Airspace: Class E ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown; Confusion; Situational Awareness
Anomaly: ATC Issue All Types; 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 Provided Assistance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: Aircraft X had a flight plan on file from ZZZ. The strip for it was in our suspense bay. When Aircraft X called up requesting IFR to [destination airport]; he said he was off ZZZ1. ZZZ is about 20 miles north of ZZZ1. As the D-side; I checked in the system for any flight plan from ZZZ1 but found none. The R-side must have seen me check or didn't care because he issued the aircraft a beacon code. By doing so; it was clear to me that the R-side wanted to build an IFR flight plan out of a VP [VFR Plan] command message; so I got right on it. He put up the tag near ZZZ1 and I built a VP because all of the info was on the IFR flight plan from ZZZ in our suspense bay. In the middle of this; there are other traffic situations for the R-side to monitor; in addition to a relief briefing that he had begun as well. He got pulled out of the relief briefing a couple of times to issue control instructions. I was inputting commands into the D-side keyboard when I heard him issue a clearance to Aircraft X. He cleared Aircraft X to '[destination airport] via direct; climb and maintain [IFR altitude].' Then he continued on with the briefing. Since I heard the aircraft get cleared and climbed; I inputted an IFR altitude into the VP to make it an FP. Truth be told; my assumption was that the R-side already had a safe vertical altitude to have given that clearance. When I looked up; I saw the M-SAW was flashing. For a moment; I didn't understand but then I realized that the aircraft was out of 4;400 feet in a 5;900 MIA. The R-side was speaking in the briefing and I was unsure as to what rule he thought he was using. Also; there might have been confusion as to the routing on the ZZZ Departure strip and what he could subsequently issue. The routing on the ZZZ Departure strip was ZZZ...[destination airport]. Also; the controller relieving him didn't say anything which compounded my confusion. Was there a rule this R-side was using? Did he think he could say 'direct' because it was on the ZZZ departure strip? In my confusion as to what legal clearance he might have given this aircraft; Aircraft X was quickly out of the 5;900 MIA. Regardless of how fast it all happened; I felt compelled to report the MIA violation as a safety concern.This R-side controller is volatile and difficult to work with. He's always right and everyone else is always wrong. I wouldn't consider him to be very professional. However; despite any differences I may have with this person; I can't fail to say something. If there was any question as to what he just did; I should have asked him despite him being in the middle of giving a relief briefing and breaking off the briefing to give control instructions.My biggest recommendation to prevent this in the future is to follow the following credo: 'See it; say it.'




Synopsis: Center Controller reported another controller identified an aircraft and made IFR below a MIA.