SR22
Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Instrument
Flight Crew Last 90 Days 200; Flight Crew Total 2700; Flight Crew Type 1320
Situational Awareness; Time Pressure
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance; Flight Crew Overcame Equipment Problem
Aircraft; Procedure
Was waiting for approach sequencing at 6000 feet. ATC asked my max speed on final and I gave them 160. ATC gave me a vector to intercept the localizer and asked that I maintain 170 knots and maintain 3000 feet until established. I was almost established when they gave me the vector in [to] intercept so I had to descend very fast to get below the glideslope; intercept; and maintain 170 knots. Typical approach speed in a SR22 is 100-120 knots but going into ZZZ this is very common to be asked to maintain 150-160. I was operating with the autopilot and upon reaching the 3000 feet altitude the autopilot did not arrest descent and the plane went well below 3000 feet before I could recognize it did not capture and disconnect the autopilot. I immediately pulled up to return to the assigned altitude. Lateral guidance was fine. ATC got a low altitude alarm and asked me to pull up within seconds of me manually arresting the descent. Climbed back to the altitude for that segment; returned to requested speed and hand flew the rest of the approach. Once over to Tower they asked [that] I slow because I was starting to encroach on the leading traffic. ATC asked if I wanted to be vectored for another attempt but since lateral guidance was maintained and the plane was climbing fine I elected to continue the approach.
SR22 pilot reported autopilot failed to level off in time and resulted in overshoot and ATC low altitude alert.