Date: 201911
Local time of day: 0001-0600
Location: PIA.TRACON, IL
Flight conditions: VMC
Light: Daylight
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class C PIA
ATC / advisory: TRACON PIA
Reporter organization: Government
Human factors: Communication Breakdown; Situational Awareness
Second reporter function: Approach; First Officer; Pilot Flying
Anomaly: ATC Issue All Types; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Procedure; Airspace Structure; Human Factors
Primary problem: Human Factors

Narrative: Aircraft X was entering the airspace descending to 10;000 feet. Aircraft X requested vectors to the runway however he did not specify an approach request. I issued him vectors for the Visual Approach to a heading of 200 and descent to an altitude of 2400 feet. Aircraft X read back the correct heading and altitude; subsequently I offered the ILS approach. Aircraft X accepted the ILS approach and was then instructed to fly heading 190. Approximately 3 minutes later I noticed Aircraft X was below the Minimum Vectoring Altitude (MVA) and ILS approach altitudes of 2;400 feet. At the time I noticed Aircraft X was below the MVA the altitude shown was 2;100 feet. I issued Aircraft X to maintain 2;400 feet. Aircraft X climbed to 2;400 feet and continued to complete a safe landing without incident. Due to possible confusion from the pilots perspective of the initial heading issued being similar to the altitude I would have been better served to split he instructions into two transmissions. The pilot had stated it had been a long day so extra vigilance on ensuring the aircraft follows instructions issued.


Second narrative: When we checked on with Approach we were given the option of the Visual Approach or vectors out for the ILS. We requested vectors out to set up for the ILS. While getting vectors from Approach for the ILS we had received instructions to fly a 200 heading and descend down to what I heard as 2;000 feet from our current altitude of 10;000 feet. Once at 2;000 feet the Captain and I both noted that the altitude was bringing us in below the final approach fix and glide slope intercept altitude of 2;400 feet. At that point we were approximately 15 miles from the final approach fix on a 190 heading vector at 2;000 feet when Approach told us to maintain 2;400 feet. We asked Approach to verify they wanted us at 2;400 feet and not 2;000 feet. They verified 2;400 and we climbed back up to 2;400 feet. Approach continued to vector us in to join the localizer for the ILS Runway 31 and to maintain 2;400 feet until established. We were then handed over to Tower after reporting the field in sight; and continued the ILS Approach to land. Once on the ground I asked Tower for Approaches phone number to call up and check with them regarding the mix up on altitudes. Once at the gate the Captain called Approach to follow up.Being at a lower altitude than intended by ATC could have potentially put us at risk of other traffic in the area. While both I and the Captain had noticed the discrepancy between the altitudes we were at and the altitude on the Approach plate; had we caught it earlier to being down at the altitude in question we would've been able to ask ATC for verification on the altitude and caught the miscommunication prior.


Synopsis: PIA Approach Controller and a First Officer reported an altitude deviation and descending below the Minimum vectoring Altitude.