Date: 201708
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Situational Awareness
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Detector: Automation Air Traffic Control; Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Human Factors; Airspace Structure
Primary problem: Human Factors

Narrative: On approach into [the airport]; ATC instructed us to turn left to a heading of 260 degrees to join the final approach course and to descend and maintain 9;000 FT. As the pilot monitoring; I was in charge of the radio calls. I read back 'left turn 260 to join; maintain 6;000 FT'. ATC did not come back and correct the altitude; and the pilot flying did not catch the erroneous read back either. Shortly after; we were cleared for a visual approach and we landed without any further incident; completely unaware that we had gone below the MVA in the area.Today I received an email from our coordinator saying that [our destination] Approach Control had recently reported an altitude deviation; as we were below the MVA in the area during our approach. Our Mode-C was reporting our altitude at 6;700 FT and the MVA in the area is 8;000 FT. Since we were not given a 'Brasher Warning' from ATC; neither the pilot flying nor myself had any idea that we were below the MVA during our approach. We were in visual conditions the entire time.I just wanted to note that my narrative above had come from the ATC report I received in the email from [our] coordinator; not from my actual memory. When I was notified about this (today); I had almost no recollection about the event as it occurred over 5 weeks ago; neither the pilot flying nor myself were told by ATC about it; and we landed without anything memorable happening.The obvious factor to this deviation is due to my incorrect read back of our assigned altitude to ATC. While we were conducting a visual approach; we were backing it up with an ILS approach. The FAF altitude is 6;000 FT; so I must have read back what I was reading on the approach chart instead of what the controller told us. ATC's failure to recognize my incorrect altitude read back also played a part in this; but it is my job to make sure that I make the right radio calls in the first place. Sometimes the fail-safes in the system don't always catch the mistakes. Obviously as the pilot monitoring; it's my responsibility to correctly read back all ATC instructions. If there is ever any doubt; I need to make sure to ask for clarification. However; mistakes do happen and incorrect read backs happen all the time. The safety nets (i.e. ATC; pilot flying) are in place to help mitigate these incorrect responses. But these backups don't always work and sometimes the mistakes slip through the system. Since we were in visual conditions and on a visual approach; we were maybe a little less 'tuned in' and ATC was maybe a little more relaxed giving us the clearance. It's imperative however to not treat a visual approach as anything less than an actual approach in regards to safety and adherence to altitudes and MVAs. If we treat the visual approaches just like the real thing; then when it comes time to shoot an approach down to minimums; it's no different and no big deal. I can honestly say that from now on I will make sure that I am much more focused and aware of the tendency for complacency during visual approaches than before.




Synopsis: EMB-175 flight crew reported that during descent; they misunderstood ATC instructions and flew under Minimum Vector Altitude.