TRACON controller described a loss of separation event when traffic on final for an ILS approach sud...

Narrative:

I vectored a PC12 for an ILS approach to runway 29R. I turned the aircraft on to final approximately 4 miles outside the final approach fix at 2;000 ft and cleared him for the approach. I gave him a frequency change to tower; and immediately after; I noticed that the aircraft was making a left turn off the final approach into higher terrain and descending to 1;700 ft. I called tower to find out if they were talking to the aircraft; they said he hadn't called. I alerted the supervisor to the problem; and continued to try and contact the PC12; without any success. I called tower again to see if he had called yet; he had not. I then made a broadcast in the blind 'PC12 is dangerously low; approaching higher terrain; and should climb immediately'. The PC12 came back on frequency advising that he was climbing. At the same time I had an AS65 at 3;000 ft in the same vicinity; and another aircraft behind the AS65 at 4;000 ft. The PC12 kept climbing through 3;000 ft; and soon as I was able I turned the aircraft away from the AS65. I was not able to maintain standard separation; due to the incident; and the pilot's actions. I had the pilot of the PC12 call us after he landed; he was very thankful for my actions; and said that he had a malfunction of the auto-pilot and was banking and descending without realizing it. Have the pilot not try to fix the auto pilot while on final approach.

Original NASA ASRS Text

Title: TRACON Controller described a loss of separation event when traffic on final for an ILS approach suddenly turned off the final in a descent and failed to respond to repeated radio calls.

Narrative: I vectored a PC12 for an ILS Approach to Runway 29R. I turned the aircraft on to final approximately 4 miles outside the final approach fix at 2;000 FT and cleared him for the approach. I gave him a frequency change to Tower; and immediately after; I noticed that the aircraft was making a left turn off the final approach into higher terrain and descending to 1;700 FT. I called Tower to find out if they were talking to the aircraft; they said he hadn't called. I alerted the Supervisor to the problem; and continued to try and contact the PC12; without any success. I called Tower again to see if he had called yet; he had not. I then made a broadcast in the blind 'PC12 is dangerously low; approaching higher terrain; and should climb immediately'. The PC12 came back on frequency advising that he was climbing. At the same time I had an AS65 at 3;000 FT in the same vicinity; and another aircraft behind the AS65 at 4;000 FT. The PC12 kept climbing through 3;000 FT; and soon as I was able I turned the aircraft away from the AS65. I was not able to maintain standard separation; due to the incident; and the pilot's actions. I had the pilot of the PC12 call us after he landed; he was very thankful for my actions; and said that he had a malfunction of the auto-pilot and was banking and descending without realizing it. Have the pilot not try to fix the auto pilot while on final approach.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1110540
Time
Date	201308
Place
Locale Reference	ZZZ.TRACON
State Reference	US
Aircraft 1
Make Model Name	PC-12
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	SA 365 Dauphin 2
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	Approach Departure
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Inflight Event / Encounter CFTT / CFIT

TRACON controller described a loss of separation event when traffic on final for an ILS approach suddenly turned off the final in a descent and failed to respond to repeated radio calls.