Narrative:

We were IFR into the washington, dc area, filed into leesburg (jyo). We shot the localizer runway 17 approach into leesburg using the autoplt without incident, but were well into the overcast and could not see the runway, so we went missed. We then elected to proceed to iad, our filed alternate, and were vectored onto a right downwind for runway 1R ILS. Everything was normal. The autoplt was flying on altitude hold and heading hold (kfc 300 feeding a sandel ehsi). The controller vectored us onto a modified right base, then an intercept heading for the localizer, but was busy and turned us late so we overshot the localizer. He gave us a northeast heading to intercept from the west, and I selected 'appr' mode on the autoplt. When the autoplt cycled from 'apr arm' to 'apr cpld,' the autoplt banked sharply to the right, directing a turn through the localizer. At that point, I disconnected the autoplt, and turned back towards the localizer. I did not turn off the flight director. XA00 is a busy time for arrs at dallas, the WX was low IFR, and everyone was busy, so the pressure to complete the approach was heavy. For some reason, I fixated on the flight director steering command bars. As I flew through the localizer from east to west, the flight director commanded a turn to the left, away from the localizer. As I turned right back to the localizer, they commanded a right turn. The command bars racked back and forth violently with heading changes, looking like a man trying to chop down a tree with a 2-BLADED axe. After turning through the localizer a second time, dallas local came on the radio, and told me that it appeared that I was left of the localizer (parallel approachs to runway 1L were in progress). I turned back to the right, ignoring the flight director. At that point, I threw in the towel, and asked for a right turn off to the east to start over and try to figure out what was going on. They vectored me onto a right downwind, with a turn onto final 5 mi or so outside the approach gate, so I had plenty of time to set up for a manual, second approach. I set the sandel to a no-map mode, and hand flew the approach. At that time, I noticed that the course bar was not set on 010, and I had to slew it manually. The controller also issued a 170 KT restr to the FAF. On final, I did slow below 170 KTS, but corrected before reaching the FAF. The next morning, I called my instructor and asked him for his evaluation and advice. He mentioned that the problem may have been interference from the runway 1L ILS, and that there was probably nothing wrong with the airplane. Today, I called garmin to discuss my adventure with them. They told me that, since the CDI (course deviation indicator) was set on VOR/localizer the whole time, the course bar on the sandel probably did not automatically slew to the final approach course at dallas, but remained on the course at leesburg. This makes more sense, as the autoplt/flight director just kept trying to turn around the shortest circle to the nearly reciprocal course at leesburg. As the tail of the aircraft swung through that course, the command bars would rack back to the opposite side, position relative to the localizer notwithstanding. What I did wrong: followed the command bars to the exclusion of all other indications and common sense. All I had to do at any point in the fiasco was to level the wings, look at the heading and localizer CDI, and correct accordingly. What I did right: admitting defeat, 'fessing up to dallas local, and asking for the turn to the east to sort things out.

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Original NASA ASRS Text

Title: SMT ENG TURBOPROP PLT HAD TRACK AND AIRSPD DEVS WHILE ATTEMPTING LOW MINIMUMS ILS APCH.

Narrative: WE WERE IFR INTO THE WASHINGTON, DC AREA, FILED INTO LEESBURG (JYO). WE SHOT THE LOC RWY 17 APCH INTO LEESBURG USING THE AUTOPLT WITHOUT INCIDENT, BUT WERE WELL INTO THE OVCST AND COULD NOT SEE THE RWY, SO WE WENT MISSED. WE THEN ELECTED TO PROCEED TO IAD, OUR FILED ALTERNATE, AND WERE VECTORED ONTO A R DOWNWIND FOR RWY 1R ILS. EVERYTHING WAS NORMAL. THE AUTOPLT WAS FLYING ON ALT HOLD AND HDG HOLD (KFC 300 FEEDING A SANDEL EHSI). THE CTLR VECTORED US ONTO A MODIFIED R BASE, THEN AN INTERCEPT HDG FOR THE LOC, BUT WAS BUSY AND TURNED US LATE SO WE OVERSHOT THE LOC. HE GAVE US A NE HDG TO INTERCEPT FROM THE W, AND I SELECTED 'APPR' MODE ON THE AUTOPLT. WHEN THE AUTOPLT CYCLED FROM 'APR ARM' TO 'APR CPLD,' THE AUTOPLT BANKED SHARPLY TO THE R, DIRECTING A TURN THROUGH THE LOC. AT THAT POINT, I DISCONNECTED THE AUTOPLT, AND TURNED BACK TOWARDS THE LOC. I DID NOT TURN OFF THE FLT DIRECTOR. XA00 IS A BUSY TIME FOR ARRS AT DALLAS, THE WX WAS LOW IFR, AND EVERYONE WAS BUSY, SO THE PRESSURE TO COMPLETE THE APCH WAS HVY. FOR SOME REASON, I FIXATED ON THE FLT DIRECTOR STEERING COMMAND BARS. AS I FLEW THROUGH THE LOC FROM E TO W, THE FLT DIRECTOR COMMANDED A TURN TO THE L, AWAY FROM THE LOC. AS I TURNED RIGHT BACK TO THE LOC, THEY COMMANDED A R TURN. THE COMMAND BARS RACKED BACK AND FORTH VIOLENTLY WITH HDG CHANGES, LOOKING LIKE A MAN TRYING TO CHOP DOWN A TREE WITH A 2-BLADED AXE. AFTER TURNING THROUGH THE LOC A SECOND TIME, DALLAS LCL CAME ON THE RADIO, AND TOLD ME THAT IT APPEARED THAT I WAS L OF THE LOC (PARALLEL APCHS TO RWY 1L WERE IN PROGRESS). I TURNED BACK TO THE R, IGNORING THE FLT DIRECTOR. AT THAT POINT, I THREW IN THE TOWEL, AND ASKED FOR A R TURN OFF TO THE E TO START OVER AND TRY TO FIGURE OUT WHAT WAS GOING ON. THEY VECTORED ME ONTO A R DOWNWIND, WITH A TURN ONTO FINAL 5 MI OR SO OUTSIDE THE APCH GATE, SO I HAD PLENTY OF TIME TO SET UP FOR A MANUAL, SECOND APCH. I SET THE SANDEL TO A NO-MAP MODE, AND HAND FLEW THE APCH. AT THAT TIME, I NOTICED THAT THE COURSE BAR WAS NOT SET ON 010, AND I HAD TO SLEW IT MANUALLY. THE CTLR ALSO ISSUED A 170 KT RESTR TO THE FAF. ON FINAL, I DID SLOW BELOW 170 KTS, BUT CORRECTED BEFORE REACHING THE FAF. THE NEXT MORNING, I CALLED MY INSTRUCTOR AND ASKED HIM FOR HIS EVALUATION AND ADVICE. HE MENTIONED THAT THE PROB MAY HAVE BEEN INTERFERENCE FROM THE RWY 1L ILS, AND THAT THERE WAS PROBABLY NOTHING WRONG WITH THE AIRPLANE. TODAY, I CALLED GARMIN TO DISCUSS MY ADVENTURE WITH THEM. THEY TOLD ME THAT, SINCE THE CDI (COURSE DEV INDICATOR) WAS SET ON VOR/LOC THE WHOLE TIME, THE COURSE BAR ON THE SANDEL PROBABLY DID NOT AUTOMATICALLY SLEW TO THE FINAL APCH COURSE AT DALLAS, BUT REMAINED ON THE COURSE AT LEESBURG. THIS MAKES MORE SENSE, AS THE AUTOPLT/FLT DIRECTOR JUST KEPT TRYING TO TURN AROUND THE SHORTEST CIRCLE TO THE NEARLY RECIPROCAL COURSE AT LEESBURG. AS THE TAIL OF THE ACFT SWUNG THROUGH THAT COURSE, THE COMMAND BARS WOULD RACK BACK TO THE OPPOSITE SIDE, POS RELATIVE TO THE LOC NOTWITHSTANDING. WHAT I DID WRONG: FOLLOWED THE COMMAND BARS TO THE EXCLUSION OF ALL OTHER INDICATIONS AND COMMON SENSE. ALL I HAD TO DO AT ANY POINT IN THE FIASCO WAS TO LEVEL THE WINGS, LOOK AT THE HDG AND LOC CDI, AND CORRECT ACCORDINGLY. WHAT I DID RIGHT: ADMITTING DEFEAT, 'FESSING UP TO DALLAS LCL, AND ASKING FOR THE TURN TO THE E TO SORT THINGS OUT.

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.