Date: 201907
Local time of day: 0601-1200
Location: BOI.Airport, ID
Flight conditions: VMC
Light: Daylight
Aircraft: Skylane 182/RG Turbo Skylane/RG
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Final Approach
Airspace: Class C BOI
ATC / advisory: Tower BOI
Second aircraft: EMB ERJ 170/175 ER/LR
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown; Confusion; Situational Awareness; Human-Machine Interface
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 Issued New Clearance
Contributing factors: Airspace Structure; Company Policy; Human Factors; Manuals; Procedure
Primary problem: Human Factors

Narrative: I turned Aircraft X below the Minimum Vectoring Altitude (MVA); not realizing he was IFR. The entire time I dealt with this Pilot; nothing he did or said led me to believe he was on an IFR flight plan nor an IFR rated pilot. He screwed up every read-back. He flew through final and lined up for the wrong runway. His phraseology was non-standard and apologetic. He screwed up his radio calls. I didn't recognize the N number as a local aircraft and he seemed unfamiliar and confused. Yes; VFR aircraft have an asterisk beside their call sign and a time-share (v) by the call sign. I missed those visual cues because all the auditory questions told me this was another student VFR pilot; probably not used to flying in controlled airspace and certainly not comfortable talking to ATC. The feeds to me on Local from the TRACON were less-than-stellar and thinking back now on the event it makes sense that I ended up trying to rectify a bad sequence with a rapid overtake on final. I wonder if the two RADAR Controllers were working together on the sequence; or even realized what they handed me until one of them called to see if I'd provide Visual Separation between the two aircraft. One Controller was a Supervisor that doesn't spend a lot of time on the scopes and was failing to ship aircraft to my frequency. I had to have Ground make a couple calls to switch aircraft to me; one of which was Aircraft Y whom I first talked to on a 2 mile final. The other Controller is someone I don't work well with. We have polar different views on working traffic; strip usage and marking; feeds to the Tower etc. So; that's the setup. Here's what happened. Aircraft X came to me from TRACON on the 10 mile range ring; a normal place to switch VFR aircraft to the Tower. I cleared him to land Runway 10R; which he read-back with his call-sign. I was working pattern traffic in the South pattern for Runway 10R; Aircraft Y. There appeared to be no conflict with Aircraft X and Aircraft Y. TRACON called me on the shout line to ask if I could provide Visual Separation with Aircraft X and Aircraft Y? I stated I would. I looked at the Tower RADAR display to figure out why he even called me about that. I found that coordination odd because the green 'VISUAL' button was illuminated indicating that I will provide Visual Separation on final; as long as wake turbulence is not an issue. When scanning the Tower RADAR display; I realized that Aircraft X was northbound; setting himself up for a 10 mile final and Aircraft Y was bearing down on him; straight-in from the West. I instructed Aircraft X to proceed direct the numbers; Runway 10R. His response was; 'We'll try.' Really? It looked like it would still work if he went to the numbers Runway 10R as long as I slowed Aircraft Y; who was tagged for the parallel runway. Well; I wasn't talking to Aircraft Y yet and thought this was because the RADAR Controller working him was slowing him to final approach speed to help this crappy sequence work. Not so. I buzzed into the RADAR Controller's ear to ask him to switch Aircraft Y as Aircraft Y was asking; 'Should we go to Tower?'I had to make a snap decision. Operating under the assumption that Aircraft X was VFR; on a 3 mile final for the wrong runway; 80 kts slower than Aircraft Y; now not enough miles in trail for the same runway. The decision was a natural. Get the VFR guy out of the way! I thought I did something good. Salvaging a bad sequence by breaking out the confused pilot who messed it all up by extending out; flying through final and lining up for the wrong runway. If he were VFR; this was the correct thing to do. There was NO WAY that sequence would work once Aircraft X aligned for Runway 10L. That was a TCAS RA or collision waiting to happen. Well; now that I understand Aircraft X was IFR; I should have called the TRACON; told them that I'm not talking to Aircraft Y; break him out. Aircraft X lined up for the left and I couldn't turn him because he was at 3;800 ft.My MVA there is 4;000 ft. The coordination from my polar opposite RADAR Controller should have been a clue that Aircraft X was IFR. Why else would he be overly concerned about visual separation? I missed it. As mentioned above; I don't operate the way that Controller does and I just chalked it up to over-coordination by him ensuring I would not allow Aircraft Y to overtake Aircraft X.All 3 of my previous facilities used an 'X' symbol and the last three digits to denote VFR aircraft. For example; Cherokee XXXYZA would be 'XYZA' for the call-sign. That was the way we did business up until a couple years ago but we made a change to full call-signs for all aircraft. Although it's been a couple of years; I still struggle with it. It is not readily apparent at a glance; who is VFR and who is IFR. Under the 'X'; last three digits way of doing business; I could walk up to any RADAR screen and instantaneously point to every VFR aircraft with 100% accuracy. Now; you have to 'scan with a purpose' to catch that little; teeny (*) or a (v) beside the call-sign to recognize who is VFR. We are busy and getting busier. We were just upgraded and we are showing increased traffic every month over years past for those months. The scope is more and more crowded. Why would we make it more difficult? You're a Controller too. You know that when you simplify as many tasks as you can; it allows you more brain power to scan and plan. Well; I missed this little gem in my scan and I was led to believe the pilot's incompetence was because he was a new pilot and I tried to do right by him; even going so far as to be overly polite and understanding with him on frequency.Without realizing it; I missed a lack of call sign use on a read back while working Local Control; and now this little gem shows me I really need to step up my game in the Tower. I am working standing up; not sitting down and chatting with coworkers. I actively scan the final and the runways; ever vigilant for wrong runway landings which we have had a rash of this past year. Now; we are under fire for massive MVA violations and now I come and add another log to the fire. I feel really bad about this.




Synopsis: A Tower Controller thought an IFR aircraft was VFR and allowed it to fly below the Minimum Vectoring Altitude.