MODIFICATION OF ACFT RESULTED IN PTU NOT OPERATING IN ACCORDANCE WITH OTHER ACFT.

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ACFT IS EQUIPPED WITH A PTU WHICH PROVIDES HYD ASSIST TO RETRACT LNDG GEAR IN THE EVENT OF A #2 ENG FAILURE. (#2 HYD SYS PROVIDES MAJORITY OF HYD CAPACITY AND OPERATES LNDG GEAR.) THUS; THE PTU IS STRICTLY A BACK UP SYSTEM AND ON ALL EARLIER MODELS WAS ACTIVATED IF AUTOFEATHER (A/FX) WAS SELECTED AND #2 AUTO FEATHERED. PTU CAN ALSO BE ACTIVATED MANUALLY BY PRESSING A GUARDED SWITCHLIGHT. DURING ORIGINAL CHKLIST (FIRST FLT OF THE DAY AND ALSO FIRST REVENUE FLT FOR THIS NEW ACFT) PTU DID NOT ACTIVATE DURING THE A/FX TEST. WE DID CHK THAT MANUAL SELECTION OPERATED PROPERLY. I HAD JUST FINISHED MY INITIAL F/O GND SCHOOL ON THE ACFT WHERE WE WERE TOLD ABOUT AN IMPENDING MODIFICATION THAT WOULD ACTIVATE THE PTU WITH A LOSS OF #2 OIL PRESSURE RATHER THAN THROUGH A/FX SIGNALS FROM #2. THIS MODEL WOULD NOT PROVIDE FOR THE PTU TO ACTIVATE DURING THE A/FX TEST. AS IT TURNED OUT; THIS LATEST ADDITION TO THE FLEET HAD BEEN MODIFIED YET WE HAD NOT BEEN TOLD THIS; HAD NO PAPERWORK AVAILABLE TO THE FLT CREWS TO VERIFY IT; NOR HAD THE MEL BEEN CHANGED TO ACCOMMODATE OPERATION OF THIS ACFT W/O PTU OPERATION DURING A/FX TEST. (THE A/FX TEST WOULD STILL BE REQUIRED BECAUSE IT TESTS OTHER FUNCTIONS NOT ASSOCIATED WITH THE PTU.) AFTER EXPLAINING THIS IMPENDING MODIFICATION TO THE CAPT WE DECIDED THE ACFT HAD INDEED BEEN MODIFIED AND ELECTED TO TAKE THE ACFT INTO REVENUE SVC SINCE WE HAD VERIFIED MANUAL OPERATION. LET ME STATE HERE THAT OUR ENG FAILURE AFTER V1 MEMORY ITEMS INCLUDE 'GEAR UP SELECT MANUAL PTU.' AFTER 3 LEGS AND A CREW SWAP THE ACFT WAS GNDED BY A WRITE UP ON THE PTU DURING A/FX TEST AS INOP. MAINT INDEED VERIFIED THAT THE ACFT HAD BEEN MODIFIED YET THE MEL GAVE NO RELIEF TO NO PTU ACTIVATION DURING THE A/FX TEST. CONCLUSION: THE XXXX HAS HAD OVER 700 MODIFICATIONS SINCE ITS INTRODUCTION. THE COMPANY NEEDS TO KEEP CLOSER TRACK OF THESE MODIFICATIONS AND IMPENDING MODIFICATIONS AND TO FORWARD THIS INFO TO THE FLT CREWS. WE ALSO SHOULD NOT HAVE TAKEN THE ACFT INTO SVC BECAUSE WE WEREN'T POSITIVELY SURE THE ACFT HAD BEEN MODIFIED AND THE MEL DOES NOT YET PROVIDE RELIEF FOR THE PTU PORTION OF THE A/FX TEST. SUPPLEMENTAL INFO FROM ACN 89532: I LEARNED THE NEXT DAY THAT THIS NEW ACFT HAD BEEN MODIFIED BY THE MFR SO THAT THE PTU DOES NOT ACTIVATE DURING THE AUTOFX TEST. EVEN THE COMPANY DID NOT KNOW THIS AND DID NOT ADVISE THE FLT CREWS OF THIS BECAUSE THEY THEMSELVES DID NOT KNOW. I ALSO LEARNED THAT THE MEL DOES NOT PROVIDE RELIEF FOR NO PTU DURING THE AUTOFX TEST.