Date: 201701
Local time of day: 1201-1800
Location: NCT.TRACON, CA
Flight conditions: VMC
Light: Daylight
Aircraft: Small Aircraft; Low Wing; 1 Eng; Retractable Gear
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Descent
Airspace: Class E NCT
ATC / advisory: TRACON NCT
Reporter organization: Government
Reporter function: Approach
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown; Situational Awareness
Second reporter function: Coordinator
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: General None Reported / Taken
Contributing factors: Airspace Structure; Human Factors; Procedure
Primary problem: Human Factors

Narrative: Aircraft X checked on my frequency at 6000 feet. After giving control instructions to other aircraft I came back to Aircraft X; issued the OAK altimeter; and asked him his requested altitude. He responded that his last assigned altitude was 6000 feet. I then asked him what his requested altitude was and he responded that he would take whatever altitude I could give him. I replied that I can give him anything he wants. He then stated how about 3000 feet. I responded that altitude was his discretion. I handed Aircraft X off to the next sector. At that point Aircraft X was descending out of 4000 feet in a 4000 foot Minimum Vectoring Altitude (MVA). He continued to descend through a 5000 foot MVA down to 3000 feet. The receiving controller did not catch the MVA violation. During this entire incident I did not register that Aircraft X was IFR and I believed that he was VFR the entire time I was working him.The low altitude alert did not go off either in the 4000 foot MVA or the 5000 foot MVA. I would recommend increased diligence of data blocks during busy sessions; and if busy ask for a hand-off.


Second narrative: I had just assumed the coordinator position. Traffic was on the busy side lots of VFR and IFR and I was going back and forth between scopes. I notice a Controller issue VFR traffic advisory to an aircraft level at 3000. I heard the response looking and I see traffic on the box. I did some other coordination then heard him say traffic no factor resume own navigation. Aircraft was still at 3000 in a 5000 MVA. I did not notice at this time he was an IFR data block; but he was talking like VFR. Something about the pilot response was weird. I did some more coordination and talked to Travis AFB ATC. Travis questioned the aircraft status as to IFR or VFR. I asked the Controller who at this time had been working it like a VFR and said he's VFR. I corrected the data block to say VFR and confirmed with Travis controller he is VFR. Did some more coordination and Travis called back and pilot had stated to them he was IFR. I was confused so I called back to verify and said we would look into it. During this whole event the aircraft had been on an IFR tag in at an altitude below the MVA and the Low Altitude Alert never went off which is more confusing. Also at the time we did not know how or when he had gotten to 3000.That aircraft should have been on the proper route when handed off. Also; the Low Altitude Alert should have gone off.


Synopsis: NCT controllers reported thinking an IFR aircraft was VFR and allowed it to proceed on its own navigation below the MVA.