DCH-8 TAXIES OVER WIG-WAG LIGHT AND IMPACTS TXWY LIGHTS.

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DARK; RAINY; WINDY; PRE-DAWN. MY FO AND I RECEIVED OUR ACFT AT THE COMPANY MAINT HANGAR; ACCOMPLISHED PREFLT AND ORIGINATING DUTIES AND COMMENCED TAXI TO DEP GATES AT THE PAX TERMINAL FOR THE START OF A 7 LEG DAY. 2 REQUIRED DAILY SYS CHKS REMAINED TO BE ACCOMPLISHED AND ELECTED TO DO THEM CLR OF THE MAINT RAMP; BUT BEFORE ARRIVING AT THE GATE. RECEIVED CLRNC TO HOLD SHORT OF RWY 10R ON TXWY F. COULD NOT GET A SATISFACTORY TEST OF AUTOFEATHER SYS; SO DECIDED TO RETURN TO HANGAR AREA. RECEIVED CLRNC TO RETURN ON TXWY F TO STARTING POINT. WAS PARKED ABOUT 10 FT SHORT OF RWY HOLD LINE AND L OF TXWY CTRLINE. ASKED FO IF IT WAS CLR R. HE PEERED THROUGH HIS RAIN-STREAKED SIDE WINDOW; AND SAID 'CLR R; PLENTY OF ROOM.' COMMENCED TURN. ABOUT 70-80 DEGS INTO TURN; SAW TAXI EDGE LIGHTS THROUGH WINDSCREEN APPEARING CLOSER THAN I EXPECTED. LOCKED R BRAKE TO CASTER NOSEWHEEL INTO TIGHTER TURN (+/- 120 DEGS CASTERING RANGE). SHORTLY THEREAFTER; HEARD A 'CLUNK' FROM NOSE AREA AND FELT WHAT I THOUGHT WAS AN UNEVENNESS IN THE PAVEMENT. NOT UNCOMMON WITH THE DHC-8 NOSEGEAR. AS WE WERE ABOUT THROUGH THE TURN; I CONTINUED; BUT ASKED FO IF HE THOUGHT I HAD HIT SOMETHING (TXWY EDGE LIGHTS LOOKED CLOSE OUT MY SIDE; BUT I WAS CERTAIN I WAS CLR OF THEM). HE DIDN'T THINK I HAD HIT ANYTHING; BUT SAID HE SUPPOSED IT WAS POSSIBLE; AS VISIBILITY WAS SOMEWHAT MARGINAL. ARRIVING AT MAINT RAMP; I ADVISED MAINT CTL OF THE PERCEIVED PROB WITH THE AUTOFEATHER SYS. (SUBSEQUENTLY LEARNED I HAD SKIPPED THE STEP OF ENERGIZING THE SYS. THIS WAS BECAUSE WE DIDN'T ACCOMPLISH A BEFORE TKOF CHKLIST; SINCE WE WERE JUST REPOSITIONING ON THE ARPT SURFACE.) MECH WITH FLASHLIGHTS INSPECTED THE NOSE AREA OF THE PLANE; WHERE WE HAD HEARD THE NOISE FROM. NOTING NOTHING UNUSUAL; AFTER LOOKING OUT AT THE TXWY (ABOUT 40-50 YARDS DISTANT) AND SEEING NOTHING AMISS; I DECIDED WE HAD HEARD A CLUNK FROM THE NOSEGEAR STRUT AS IT TRANSITED SOME UNEVEN PAVEMENT. MADE A MAINT LOG ENTRY FOR THE AUTOFEATHER SYS I BELIEVED TO BE INOP; AND WE TOOK A DIFFERENT AIRPLANE TO START OUR DAY. IT WAS WHEN I WAS UNABLE TO GET THE SAME SYS ON THE SECOND ACFT TO TEST NORMALLY THAT I LEARNED I HAD NOT SWITCHED EITHER SYS ON. IT WAS STILL DARK WHEN WE TAXIED VIA THE SAME TXWY AS BEFORE. PASSING THE SPOT WHERE WE HAD TURNED AROUND; THE FO LOOKED OUT AND COMMENTED THAT ALL THE TXWY EDGE LIGHTS LOOKED UNTOUCHED. WE COMPLETED THE DAY'S FLTS. UPON ARRIVING AT PDX THAT EVENING; WE WERE INFORMED A SMGCS HOLD LINE 'WIG-WAG' LIGHT HAD BEEN FLATTENED WHERE WE TURNED AROUND EARLY THAT DAY. I EXPLAINED I HAD NOT MADE A LOGBOOK ENTRY PERTAINING TO THE NOISE WE HEARD; BECAUSE WE BOTH HAD CONCLUDED THAT IT HAD BEEN A NOT UNCOMMON SOUND MADE BY THE NOSEGEAR STRUT AS WE CROSSED SOME UNEVEN PAVEMENT. I NOW BELIEVE A POSSIBLE EXPLANATION IS THAT MY L MAIN GEAR RODE OVER THE WIG-WAG LIGHT AND FLATTENED IT; AND THE NOSE GEAR 'CLUNKED' AS THE AIRPLANE ROCKED SLIGHTLY AS THE GEAR RODE OVER THE LIGHT ASSEMBLY. THIS WOULD EXPLAIN WHY IT FELT LIKE THE NOSE GEAR WENT THROUGH A SHALLOW DIP. THE DHC-8 HAS A WIDE TRACK (26 FT BTWN MAIN GEAR) AND THE GEAR IS NOT VISIBLE FROM THE COCKPIT. I BELIEVE I FAILED TO TAKE INTO ACCOUNT HOW FAR OUT THE MAIN GEAR WAS; AND ALSO MISJUDGED MY DISTANCE FROM THE LIGHTS DURING THE TURN. MARGINAL VISIBILITY I BELIEVE AGGRAVATED THIS PROB. I SUBSEQUENTLY LEARNED THAT 2 BLUE TXWY EDGE LIGHTS ALSO WERE DAMAGED. CAUSAL FACTORS I BELIEVE INCLUDE: 1) MY DECISION TO ATTEMPT A 180 DEG TURN ON A RATHER NARROW TXWY WITHOUT BENEFIT OF A WINGWALKER. 2) DEPTH PERCEPTION HAMPERED BY RAIN-STREAKED WINDOWS. 3) FEELING OF TIME PRESSURE (SELF- IMPOSED) TO TRY TO MAKE AN ON-TIME DEP CLOUDED MY JUDGEMENT. I SHOULD HAVE TAKEN TIME TO RECEIVE CLRNC TO A WIDE TURNAROUND; SUCH AS ONTO THE RWY. WHAT I WOULD DO DIFFERENTLY: 1) ACCOMPLISH BEFORE TKOF CHKLIST BEFORE ATTEMPTING SYS CHKS WHICH REQUIRE SWITCHES TO BE CONFIGURED FOR TKOF. IF A SYS DOESN'T TEST; CONSULT MANUAL TO VERIFY I'VE COMPLETED ALL STEPS BEFORE RETURNING ACFT TO MAINT. 2) FIND WIDER SPOT OR GET WING WALKER ASSISTANCE BEFORE TURNING AROUND; ESPECIALLY WITH MARGINAL VISIBILITY. 3) IF I THINK I EVEN POSSIBLY COULD HAVE HIT SOMETHING WITH THE ACFT; MAKE A MAINT LOG ENTRY DOCUMENTING IT. 4) NEVER FORGET THAT MY MAIN GEAR ARE 26 FT APART; AND I CAN'T SEE EITHER ONE OF THEM. 5) DON'T LET 'GET GOINGITIS' (OR GET HOMEITIS) TEMPT ME TO TAKE SHORTCUTS.