Narrative:

First officer flying sfo-iad. 3 hours late departure due to inbound aircraft with mechanical problem with a flight computer. During flight, same problem surfaces with the computer 'slat, flap control computer.' worked problem with maintenance en route and it cleared. On approach, first officer (very good SOP and book knowledge) high and fast on GS. Due to stabilized approach requirements, inside OM, a go around was executed. Gear and flaps had been extended normally. Gear retract normal. Did checklist and advised passenger of go around. First officer now ready for second approach -- speed 180 KTS. Flaps 2 degrees as SOP. Approaching OM, gear down and final checklist. Time to extend and sounds were not normal. As I reached for gear handle to 'jiggle it' -- ie, to see if it was in proper position -- an ECAM warning annunciated. Gear not down was message, and fix was to gravity extend gear. However, gear not down warning was partial. Message and warning incomplete also. This warning comes on at 750 ft RA, not 1500 ft RA. Engines/throttles were not idle due to cognitive belief warning was in error and 'slat, flap, control computer' perhaps involved. Time/sequence of gear not normal. Verbal discussions with instructors at our training facility during training to 'cycle gear to change gear computer #1 to #2.' I chose to cycle gear. Warning cleared, gear computer changed from #1 to #2 and gear extended normally. Gear computer, known as landing gear control interface unit #1, found to have internal fault not idented on warning screen. Slat, flap, control computer has a link to landing gear control interface unit #1. Subsequent history on aircraft -- both landing gear control interface units replaced. I believe cognitive thought process was instrumental in assessment and actions involved. Gravity extend of gear eliminates nosewheel steering on slippery runways and would require tug to gate. Did not blindly follow aircraft alert. I had concern of second missed approach to passenger fear. Concern on night landing with nosewheel steering inoperative due gravity extension. Although ECAM message said gravity gear extension, I had strong cognitive thoughts that slat, flap, control computer problem was involved. Sequence time to retract is addressed in flight manual to recycle, but not addressed on landing fault. Callback conversation with reporter revealed the following information: flight crew, first officer flying, made a missed approach because of high airspeed on final. When the aircraft was lined up and stabilized for the next approach, the flight crew lowered the landing gear but the sound of the landing gear extending was different to the reporter. This gave a message to gravity fall the landing gear. The reporter captain didn't want to free fall the landing because it would take longer to do and force another missed approach. He didn't want the passenger to be concerned over another missed approach event. Also, if the landing gear should extend by gravity, there would be no nosewheel steering available forcing the aircraft to be towed to the gate by a tug. The reporter then decided to raise the landing gear and extend it one more time. By doing this, another landing gear control interface unit would be activated to control landing gear extension. With each retraction of the landing gear, the alternate landing gear control interface unit is activated for the next gear extension. This worked successfully except it did not show the right main gear door as being in the proper position for landing. The landing gear was down and locked so the reporter decided to land and taxi to the gate. A landing gear unsafe warning did appear on the ECAM, but other indications showed the landing gear to be safely extended. Flight crew decided to land and taxi to the gate, which was done successfully. It turned out that the landing gear control interface unit #1 had a broken wire which was causing faulty warnings. By simply raising and lowering the landing gear, the landing gear control interface unit was changed to one that was working properly for a good gear extension.

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Original NASA ASRS Text

Title: AN A320 LNDG AT IAD, HAS LNDG EXTENSION PROBS CAUSED BY A FAULTY LNDG GEAR COMPUTER UNIT. PLT SWITCHES TO ALTERNATE LNDG GEAR COMPUTER UNIT AND LANDS SAFELY.

Narrative: FO FLYING SFO-IAD. 3 HRS LATE DEP DUE TO INBOUND ACFT WITH MECHANICAL PROB WITH A FLT COMPUTER. DURING FLT, SAME PROB SURFACES WITH THE COMPUTER 'SLAT, FLAP CTL COMPUTER.' WORKED PROB WITH MAINT ENRTE AND IT CLRED. ON APCH, FO (VERY GOOD SOP AND BOOK KNOWLEDGE) HIGH AND FAST ON GS. DUE TO STABILIZED APCH REQUIREMENTS, INSIDE OM, A GAR WAS EXECUTED. GEAR AND FLAPS HAD BEEN EXTENDED NORMALLY. GEAR RETRACT NORMAL. DID CHKLIST AND ADVISED PAX OF GAR. FO NOW READY FOR SECOND APCH -- SPD 180 KTS. FLAPS 2 DEGS AS SOP. APCHING OM, GEAR DOWN AND FINAL CHKLIST. TIME TO EXTEND AND SOUNDS WERE NOT NORMAL. AS I REACHED FOR GEAR HANDLE TO 'JIGGLE IT' -- IE, TO SEE IF IT WAS IN PROPER POS -- AN ECAM WARNING ANNUNCIATED. GEAR NOT DOWN WAS MESSAGE, AND FIX WAS TO GRAVITY EXTEND GEAR. HOWEVER, GEAR NOT DOWN WARNING WAS PARTIAL. MESSAGE AND WARNING INCOMPLETE ALSO. THIS WARNING COMES ON AT 750 FT RA, NOT 1500 FT RA. ENGS/THROTTLES WERE NOT IDLE DUE TO COGNITIVE BELIEF WARNING WAS IN ERROR AND 'SLAT, FLAP, CTL COMPUTER' PERHAPS INVOLVED. TIME/SEQUENCE OF GEAR NOT NORMAL. VERBAL DISCUSSIONS WITH INSTRUCTORS AT OUR TRAINING FACILITY DURING TRAINING TO 'CYCLE GEAR TO CHANGE GEAR COMPUTER #1 TO #2.' I CHOSE TO CYCLE GEAR. WARNING CLRED, GEAR COMPUTER CHANGED FROM #1 TO #2 AND GEAR EXTENDED NORMALLY. GEAR COMPUTER, KNOWN AS LNDG GEAR CTL INTERFACE UNIT #1, FOUND TO HAVE INTERNAL FAULT NOT IDENTED ON WARNING SCREEN. SLAT, FLAP, CTL COMPUTER HAS A LINK TO LNDG GEAR CTL INTERFACE UNIT #1. SUBSEQUENT HISTORY ON ACFT -- BOTH LNDG GEAR CTL INTERFACE UNITS REPLACED. I BELIEVE COGNITIVE THOUGHT PROCESS WAS INSTRUMENTAL IN ASSESSMENT AND ACTIONS INVOLVED. GRAVITY EXTEND OF GEAR ELIMINATES NOSEWHEEL STEERING ON SLIPPERY RWYS AND WOULD REQUIRE TUG TO GATE. DID NOT BLINDLY FOLLOW ACFT ALERT. I HAD CONCERN OF SECOND MISSED APCH TO PAX FEAR. CONCERN ON NIGHT LNDG WITH NOSEWHEEL STEERING INOP DUE GRAVITY EXTENSION. ALTHOUGH ECAM MESSAGE SAID GRAVITY GEAR EXTENSION, I HAD STRONG COGNITIVE THOUGHTS THAT SLAT, FLAP, CTL COMPUTER PROB WAS INVOLVED. SEQUENCE TIME TO RETRACT IS ADDRESSED IN FLT MANUAL TO RECYCLE, BUT NOT ADDRESSED ON LNDG FAULT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: FLC, FO FLYING, MADE A MISSED APCH BECAUSE OF HIGH AIRSPD ON FINAL. WHEN THE ACFT WAS LINED UP AND STABILIZED FOR THE NEXT APCH, THE FLC LOWERED THE LNDG GEAR BUT THE SOUND OF THE LNDG GEAR EXTENDING WAS DIFFERENT TO THE RPTR. THIS GAVE A MESSAGE TO GRAVITY FALL THE LNDG GEAR. THE RPTR CAPT DIDN'T WANT TO FREE FALL THE LNDG BECAUSE IT WOULD TAKE LONGER TO DO AND FORCE ANOTHER MISSED APCH. HE DIDN'T WANT THE PAX TO BE CONCERNED OVER ANOTHER MISSED APCH EVENT. ALSO, IF THE LNDG GEAR SHOULD EXTEND BY GRAVITY, THERE WOULD BE NO NOSEWHEEL STEERING AVAILABLE FORCING THE ACFT TO BE TOWED TO THE GATE BY A TUG. THE RPTR THEN DECIDED TO RAISE THE LNDG GEAR AND EXTEND IT ONE MORE TIME. BY DOING THIS, ANOTHER LNDG GEAR CTL INTERFACE UNIT WOULD BE ACTIVATED TO CTL LNDG GEAR EXTENSION. WITH EACH RETRACTION OF THE LNDG GEAR, THE ALTERNATE LNDG GEAR CTL INTERFACE UNIT IS ACTIVATED FOR THE NEXT GEAR EXTENSION. THIS WORKED SUCCESSFULLY EXCEPT IT DID NOT SHOW THE R MAIN GEAR DOOR AS BEING IN THE PROPER POS FOR LNDG. THE LNDG GEAR WAS DOWN AND LOCKED SO THE RPTR DECIDED TO LAND AND TAXI TO THE GATE. A LNDG GEAR UNSAFE WARNING DID APPEAR ON THE ECAM, BUT OTHER INDICATIONS SHOWED THE LNDG GEAR TO BE SAFELY EXTENDED. FLC DECIDED TO LAND AND TAXI TO THE GATE, WHICH WAS DONE SUCCESSFULLY. IT TURNED OUT THAT THE LNDG GEAR CTL INTERFACE UNIT #1 HAD A BROKEN WIRE WHICH WAS CAUSING FAULTY WARNINGS. BY SIMPLY RAISING AND LOWERING THE LNDG GEAR, THE LNDG GEAR CTL INTERFACE UNIT WAS CHANGED TO ONE THAT WAS WORKING PROPERLY FOR A GOOD GEAR EXTENSION.

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.