AN ACR B727 FLC HAD THE #2 OIL FILTER BYPASS WARNING ILLUMINATE SEVERAL TIMES DURING A FLT AND EACH TIME THEY WERE ABLE TO EXTINGUISH THE LIGHT USING THE CHKLIST PROC; EXCEPT THAT DURING CRUISE THEY FOUND THAT THE LIGHT WOULD STAY OUT IF THE #2 ENG WAS OPERATED AT IDLE. THE FLC DECIDED TO DIVERT TO ELP WHERE THE WARNING SYS WAS FOUND TO BE FAULTY AND PLACARDED.

Narrative

JUL/XA/97; FLT #1 (IAH-LAS) AND FLT #2 (LAS-IAH). PRIOR TO FLT #1; UPON ARR AT ACFT; I DISCOVERED A PLACARD ON THE MAINT LOG WHICH STATED THAT THE #2 OIL FILTER BYPASS WARNING LIGHT WAS INOP. I OPENED THE MEL (SYS 79-2) AND FOUND THAT (M) 'ONE MAY BE INOP PROVIDED: A) MALFUNCTION IS IN THE WARNING SYS; AND B) MAIN OIL SCREEN IS INSPECTED FOR PRESENCE OF CONTAMINANTS AT LEAST EVERY 12 HRS.' AFTER LOOKING THROUGH THE LOG I CAME TO THE CONCLUSION THAT THERE WAS NO 'TIME' WRITTEN DOWN THAT WOULD SATISFY THE 'EVERY 12 HRS' PART OF THE MEL REQUIREMENT. I IMMEDIATELY CALLED MAINT OVER THE RADIO TO RPT THIS AND THEY SAID THAT A MECH WOULD INSPECT THE FILTER AND MAKE THE 'TIME' ENTRY IN THE LOG. THE MECH CAME TO THE COCKPIT AND SAID THEY INTENDED TO 'FIX' THE INDICATOR. AFTER A PERIOD OF TIME THE MECH CAME BACK TO THE COCKPIT; RAN THE #2 ENG AND REMOVED THE PLACARD FROM THE WARNING LIGHT. (SWITCH TO LAS VEGAS.) PRIOR TO DEP TIME OF FLT #2; IN LAS; AN FAA ACI MADE HIS PRESENCE AND JUMP SEAT INTENTIONS KNOWN TO ME. AFTER PUSHBACK/DISCONNECT AND AT THE START OF TAXI OUT; OUR #2 OIL FILTER BYPASS WARNING LIGHT ILLUMINATED FOR A BRIEF PERIOD OF TIME. EVEN THOUGH THE LIGHT WAS NO LONGER ILLUMINATED; WE STOPPED OUR TAXI AND GOT INTO AND WENT THROUGH THE ABNORMAL CHKLIST. AFTER THE CHKLIST; THE 3 OF US DISCUSSED THE INDICATION. BECAUSE OF THE 'HISTORY' OF THE INDICATING SYS AND BECAUSE THE LIGHT HAD COME ON FOR SUCH A SHORT TIME AND THEN HAD GONE OUT; WE CAME TO THE CONCLUSION THAT A 'LIGHT ON' WAS A MALFUNCTION IN THE WARNING SYS RATHER THAN AN ACTUAL FILTER PROB -- SO WE CONTINUED. AFTER A LENGTHY TAXI TIME (DURING WHICH THE LIGHT REMAINED OUT) WE WERE CLRED INTO POS FOR TKOF. AS WE TURNED ONTO THE RWY I TOLD THE FO THAT IF THE LIGHT CAME ON DURING THE TKOF ROLL MY COURSE OF ACTION WOULD BE TO CONTINUE THE TKOF RATHER THAN REJECT. I UNDERSTAND THAT THE FAA JUMP SEATER STATES THAT THE LIGHT DID ILLUMINATE DURING THE TKOF ROLL(?) HOWEVER; I HONESTLY DON'T REMEMBER IF IT DID OR NOT.WE CONTINUED A NORMAL FLT TOWARDS HOUSTON UNTIL JUST W OF EL PASO; AT WHICH POINT WE GOT ANOTHER 'LIGHT.' WE WENT THROUGH THE ABNORMAL CHKLIST AGAIN AND OVER A PERIOD OF TIME DISCOVERED THAT IN ORDER TO KEEP THE LIGHT 'OUT' WE HAD TO HAVE THE #2 PWR LEVER PROGRESSIVELY TOWARDS THE IDLE POS. I WAS NOW HAVING SECOND THOUGHTS ABOUT THE INDICATOR -- THAT IT MIGHT BE THE FILTER AND THAT WE MIGHT HAVE TO SHUT THE ENG DOWN. WE WERE AT A VERY HVY WT (APPROX 160000 LBS) AND WITH AN ISA OF APPROX +15 DEGS; IT WAS BECOMING EVIDENT THAT WE COULDN'T MAINTAIN CRUISE ALT WITH MAX CONTINUOUS PWR ON #1 AND #3 WITH #2 PULLED BACK TO IDLE. THE WX AT LOWER ALTS BTWN EL PASO AND HOUSTON WAS QUESTIONABLE AND WE HAD AUSTIN AS AN ALTERNATE FOR HOUSTON. I DISCUSSED MY CONCERNS WITH THE CREW ABOUT THE POSSIBILITY OF HAVING TO SHUT #2 ENG DOWN; THE WX AT LOWER CRUISING ALTS; AND THE SLIM POSSIBILITY OF HAVING TO DIVERT TO AUSTIN FROM HOUSTON -- WITH AN ENG SHUT DOWN; AND WE AGREED THAT THE SAFEST COURSE OF ACTION WAS TO DIVERT INTO EL PASO; APPROX 50 MI FROM OUR POS AND HAVING GOOD WX. WE DID DIVERT TO EL PASO. AFTER A DELAY IN EL PASO OF APPROX 4-5 HRS; THE CONTRACT MAINT MAN DISCOVERED OUR PROB WAS; IN FACT; A FAULTY INDICATING SYS (AS PER ITS HISTORY) RATHER THAN A FILTER PROB. A PLACARD WENT BACK ON THE SYS AND WE WERE SENT ON OUR WAY TO HOUSTON. BY THE WAY; SOMETIME AFTER OUR ARR IN EL PASO; OUR FAA ACM DISCOVERED THAT THERE WAS A B737 ACFT AT ANOTHER GATE THAT WAS ABOUT TO LEAVE FOR HOUSTON AND HE CHOSE TO CONTINUE HIS FLT ON THAT ACFT RATHER THAN WAITING FOR OUR RELEASE. I COMPLETED A CAPT'S IRREGULARITY RPT AND CALLED THE OPS DIRECTOR IN SYS CTL WHILE IN EL PASO. SUPPLEMENTAL INFO FROM ACN 375184: WE WERE CLRED TO TAKE OFF IN LAS VEGAS; WITH AN FAA INSPECTOR IN THE JUMP SEAT. AFTER DOING THE BEFORE TKOF CHKLIST; I FOCUSED MY ATTN ON THE FE PANEL UNTIL 100 KTS; WHICH IS SOP. AT ABOUT THIS TIME; I LOOKED FORWARD; AND SAW THE OIL FILTER BYPASS LIGHT WAS ON. THE FAA INSPECTOR CALLED OUT THAT THE LIGHT WAS ON. ONCE IN THE AIR; AS PER THE ABNORMAL CHKLIST; WE RETARDED THE THROTTLE UNTIL THE LIGHT WENT OUT; PUSHING THE THROTTLE ALL THE WAY FORWARD TO CLB PWR; THE LIGHT REMAINED OUT. THE LIGHT STAYED OUT UNTIL WE NEARED EL PASO; AT WHICH TIME IT CAME BACK ON. WE DECIDED TO MAKE AN UNSCHEDULED LNDG IN EL PASO TO HAVE IT CHKED. THE FILTER WAS CHKED; AND NOTHING WAS FOUND WRONG; AND THE OIL FILTER BYPASS LIGHT WAS PLACARDED INOP; ONCE AGAIN. WE THEN PROCEEDED ROUTINELY TO HOUSTON; WITH THE LIGHT ILLUMINATED AND PLACARDED.