Narrative:

I was flying from aus to hou on an IFR flight plan. My clearance was radar vectors to tnv and a struk 8 arrival to hou. I was assigned a 4000 ft altitude and told to expect 7000 ft 10 mins after departure, hou was landing on ILS runway 13R. The WX at hou was 1000 ft overcast with 600 ft broken. Visibility was 3 mi with rain showers. The plane is a mooney M20C/G and is equipped with a bendix/king 90B GPS and an s-tec 30 autoplt. I programmed the GPS prior to takeoff. I was initially between layers at 7000 ft, but as I approached tnv, I was in the clouds. Since the temperature was near freezing, I requested and received permission to descend to 5000 ft. Shortly after reaching tnv, ZHU passed me over to houston approach and I was vectored to intercept the ILS runway 13R. At that point I switched the autoplt to the heading mode and put the GPS in the obs mode with the obs set on 130 degrees and in the super navigation 5 display. My last instructions prior to the incident I am reporting were to turn to a heading of 090 degrees, descend to 2000 ft and intercept the ILS. I was asked to try to keep up my speed up if possible. I turned as instructed, descended to 2000 ft, and activated the altitude and heading hold on the autoplt. Since the needles were pegged, I started to monitor my approach to the ILS on the GPS screen. The first indication of trouble was when the controller instructed me to turn to a heading of 200 degrees and climb to 3000 ft at once. When I turned my attention to my flight instruments, I realized that the plane was in a bank of over 30 degrees and had lost over 500 ft. The autoplt had become disengaged. I followed instructions, was vectored back to the ILS and landed without further difficulty. Probable causes: 1) I may have inadvertently hit the autoplt disconnect switch on the yoke. The autoplt aural warning is not audible when the engine is running and the pilot is wearing headphones. 2) the s-tec 30 unit on my plane is defective and it may have turned itself off. I tested the autoplt and found that if I used the panel mounted push mode knob to disengage the autoplt, the autoplt would freeze and would not accept commands from either the push mode knob or the yoke mounted switches. This happened 3 times on jan/xa/01. The first time was when I tested the autoplt at hou prior to flying it to iws. I was able to restore the autoplt to normal function by turning the autoplt off with the panel switch. When I arrived at iws, I asked a commercial pilot (IFR rated) to witness the phenomena. We were able to replicate the failure twice. The first time we were able to restore the autoplt to normal function by turning off the autoplt with the panel switch. The second time we were able to restore the autoplt to normal function only after we pulled the circuit breaker. After that, the autoplt did not malfunction again. The autoplt has disengaged several times in the past in non IMC. I had always assumed I had inadvertently hit the autoplt disconnect switch on the yoke. Now I am not sure that was the case.

Google
 

Original NASA ASRS Text

Title: PLT OF A MOONEY 20 LOST CTL OF THE ACFT DURING TRANSITION TO AN ILS APCH CAUSING APCH CTLR TO INTERVENE AND VECTOR HIM ON A MISSED APCH AND BACK FOR ANOTHER APCH WHICH WAS SUCCESSFUL.

Narrative: I WAS FLYING FROM AUS TO HOU ON AN IFR FLT PLAN. MY CLRNC WAS RADAR VECTORS TO TNV AND A STRUK 8 ARR TO HOU. I WAS ASSIGNED A 4000 FT ALT AND TOLD TO EXPECT 7000 FT 10 MINS AFTER DEP, HOU WAS LNDG ON ILS RWY 13R. THE WX AT HOU WAS 1000 FT OVCST WITH 600 FT BROKEN. VISIBILITY WAS 3 MI WITH RAIN SHOWERS. THE PLANE IS A MOONEY M20C/G AND IS EQUIPPED WITH A BENDIX/KING 90B GPS AND AN S-TEC 30 AUTOPLT. I PROGRAMMED THE GPS PRIOR TO TKOF. I WAS INITIALLY BTWN LAYERS AT 7000 FT, BUT AS I APCHED TNV, I WAS IN THE CLOUDS. SINCE THE TEMP WAS NEAR FREEZING, I REQUESTED AND RECEIVED PERMISSION TO DSND TO 5000 FT. SHORTLY AFTER REACHING TNV, ZHU PASSED ME OVER TO HOUSTON APCH AND I WAS VECTORED TO INTERCEPT THE ILS RWY 13R. AT THAT POINT I SWITCHED THE AUTOPLT TO THE HDG MODE AND PUT THE GPS IN THE OBS MODE WITH THE OBS SET ON 130 DEGS AND IN THE SUPER NAV 5 DISPLAY. MY LAST INSTRUCTIONS PRIOR TO THE INCIDENT I AM RPTING WERE TO TURN TO A HDG OF 090 DEGS, DSND TO 2000 FT AND INTERCEPT THE ILS. I WAS ASKED TO TRY TO KEEP UP MY SPD UP IF POSSIBLE. I TURNED AS INSTRUCTED, DSNDED TO 2000 FT, AND ACTIVATED THE ALT AND HDG HOLD ON THE AUTOPLT. SINCE THE NEEDLES WERE PEGGED, I STARTED TO MONITOR MY APCH TO THE ILS ON THE GPS SCREEN. THE FIRST INDICATION OF TROUBLE WAS WHEN THE CTLR INSTRUCTED ME TO TURN TO A HDG OF 200 DEGS AND CLB TO 3000 FT AT ONCE. WHEN I TURNED MY ATTN TO MY FLT INSTS, I REALIZED THAT THE PLANE WAS IN A BANK OF OVER 30 DEGS AND HAD LOST OVER 500 FT. THE AUTOPLT HAD BECOME DISENGAGED. I FOLLOWED INSTRUCTIONS, WAS VECTORED BACK TO THE ILS AND LANDED WITHOUT FURTHER DIFFICULTY. PROBABLE CAUSES: 1) I MAY HAVE INADVERTENTLY HIT THE AUTOPLT DISCONNECT SWITCH ON THE YOKE. THE AUTOPLT AURAL WARNING IS NOT AUDIBLE WHEN THE ENG IS RUNNING AND THE PLT IS WEARING HEADPHONES. 2) THE S-TEC 30 UNIT ON MY PLANE IS DEFECTIVE AND IT MAY HAVE TURNED ITSELF OFF. I TESTED THE AUTOPLT AND FOUND THAT IF I USED THE PANEL MOUNTED PUSH MODE KNOB TO DISENGAGE THE AUTOPLT, THE AUTOPLT WOULD FREEZE AND WOULD NOT ACCEPT COMMANDS FROM EITHER THE PUSH MODE KNOB OR THE YOKE MOUNTED SWITCHES. THIS HAPPENED 3 TIMES ON JAN/XA/01. THE FIRST TIME WAS WHEN I TESTED THE AUTOPLT AT HOU PRIOR TO FLYING IT TO IWS. I WAS ABLE TO RESTORE THE AUTOPLT TO NORMAL FUNCTION BY TURNING THE AUTOPLT OFF WITH THE PANEL SWITCH. WHEN I ARRIVED AT IWS, I ASKED A COMMERCIAL PLT (IFR RATED) TO WITNESS THE PHENOMENA. WE WERE ABLE TO REPLICATE THE FAILURE TWICE. THE FIRST TIME WE WERE ABLE TO RESTORE THE AUTOPLT TO NORMAL FUNCTION BY TURNING OFF THE AUTOPLT WITH THE PANEL SWITCH. THE SECOND TIME WE WERE ABLE TO RESTORE THE AUTOPLT TO NORMAL FUNCTION ONLY AFTER WE PULLED THE CIRCUIT BREAKER. AFTER THAT, THE AUTOPLT DID NOT MALFUNCTION AGAIN. THE AUTOPLT HAS DISENGAGED SEVERAL TIMES IN THE PAST IN NON IMC. I HAD ALWAYS ASSUMED I HAD INADVERTENTLY HIT THE AUTOPLT DISCONNECT SWITCH ON THE YOKE. NOW I AM NOT SURE THAT WAS THE CASE.

Data retrieved from NASA's ASRS site as of July 2007 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.