SR22
Flight Crew Commercial; Flight Crew Instrument
Human-Machine Interface; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Executed Go Around / Missed Approach; Flight Crew Returned To Clearance
Human Factors; Aircraft
I was flying in IMC intending the ILS approach at CRQ. I was receiving vectors and was flying with the autopilot engaged. Upon reaching the approach path; I engaged the NAV/APPR function on the autopilot. The autopilot indicated that it was engaged. The plane began its turn inbound and I started a descent having become established on course. The autopilot disengaged without an audible alert and I didn't immediately realize it and ended up off course.At that point I was contacted by ATC with an altitude alert and asked if I intended to try to complete the approach. I said I was having a problem. They gave me a climb back to 4;000 FT and a new heading. I went where directed and was vectored back for the approach which I then hand flew without further incident.
An SR22 pilot failed to note the autopilot had disconnected upon intercepting the ILS to CRQ. ATC received an altitude alert and provided vectors back for a successful hand flown ILS.