Date: 201904
Local time of day: 1801-2400
Location: ZSE.ARTCC, WA
Aircraft: Skylane 182/RG Turbo Skylane/RG
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Flight phase: Cruise
Airspace: Class E ZSE
ATC / advisory: Center ZSE
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown; Fatigue; Situational Awareness
Anomaly: ATC Issue All Types; 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; Airspace Structure
Primary problem: Human Factors

Narrative: There are several factors that contributed to this situation; but first; here is the actual occurrence: Spokane Approach Control (GGG) called and asked to give me a manual hand-off on an IFR aircraft (Aircraft X) as they couldn't get the aircraft flight plan info to pass. GGG said the aircraft was going to SZT via direct CESIG. I didn't copy the approach request at the time. I was too busy thinking about tagging this aircraft up so that it wouldn't be an IFR limited data block in my airspace. So I assigned the aircraft a beacon code; started a VFR flight plan; routed the flight plan the way GGG said; and had GGG assign that aircraft the code I assigned. They asked if I would like them to assign the approach or if I wanted to. By the letter of agreement; they should assign it but since they were calling on a questionable flight plan; I assume that is why they asked.I had just sat down; just finished receiving a relief briefing; not a full minute in when they called. The controller giving me the relief briefing even said as he was finishing; 'And Spokane is calling you.' In response to GGG's question 'to clear or not to clear;' I responded that I would take care of assigning the aircraft the approach so I asked for control and GGG approved. All this was done prior to me inputting a hard IFR altitude of 8;000 feet. Once I did; though; the MSAW [Minimum Safe Altitude Warning] went off; alerting me to the 9;000 ft. terrain about a minute from the aircraft's flight path. Aircraft X got shipped to me just after I inputted a hard IFR 8;000 feet. altitude so I climbed him to 9;000 feet. The aircraft entered the 9;000 MIA [Minimum IFR Altitude] while climbing to 9;000. He crossed CESIG at 9;000 and was cleared safely for the RNAV Y 20 approach into SZT. I called GGG later and asked them what their MIA is all the way to CESIG and they said that they can use down to 7;900 feet.Factors that contributed to this occurrence:1. Just sitting down into the sector2. A new approach (the RNV Y 20 is brand new)3. A modified letter of agreement with GGG that gives them Carte Blanche for the kind of approach they can issue on radar hand-off going into SZT4. Different MIAs for Approach Control and for Enroute facilities5. Electronic flight plan info that didn't passThe first thing I would do differently is to allow GGG to issue the approach. If their MIAs are lower; it's a no-brainer. However; regarding this issue; I would recommend that we all use the same MIAs. We're filtering their radar anyway. Why do we have higher MIAs?The second thing I would do would be to solidify which one approach GGG can issue. That way; there's no confusion; there's no ambiguity. Or; since SZT is so close to GGG; have GGG take the airspace over SZT. That would eliminate coordination on these aircraft as well as other departure aircraft off COE.This situation went from bad to worse in about a minute. I climbed the aircraft as that was the only safe thing I felt I could do. By the time he was on my frequency; I might have been able to turn him eastbound to avoid the MIA as he was a slow mover but since he was only a minute away (or less) I felt that wasn't safe. I knew our terrain should be about 1;700 feet. below the MIA; so I knew the aircraft was safe without yanking or banking it. I didn't think cranking him to a 050 heading was prudent given he'd also be climbing and having to make another hard turn back to CESIG.  I could have shipped him back to GGG and told them to issue the approach because they have lower MIAs but by the time Aircraft X was on my frequency; I had very little time to react. Besides; if I sent him back to GGG; what sort of disaster might have happened if we lost communications on him? The safest thing; I felt; I was to climb him immediately. I did assign 9;000 before he entered the 9;000 MIA.




Synopsis: Seattle Center Controller reported an aircraft was below the MIA which was different than the TRACON's MIA.