A B747-400 WAS DISPATCHED IN NON COMPLIANCE WITH #3 PACK DEFERRED ON TAXI OUT VIA SATCOM. FAILED TO LOCK CLOSED THE PACK SHUTOFF VALVE PER MEL.

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RECEIVED A SATCOM PATCH VIA OUR DISPATCH DEPT; HAD A B747-400 THAT RPTED THE #3 PACK WAS INOP WITH ASSOCIATED EICAS MESSAGE AND ACFT WAS TAXIING FOR TKOF. I PULLED UP THE ASSOCIATED MEL FOR #3 PACK INOP; ADVISED CREW THAT THERE WAS NO OPERATIONAL IMPACT FOR THEIR FLT AND GAVE THEM THE DEFERRAL AUTH OVER THE SAT PHONE AND SENT A COPY OF THE MEL AND A NEW MAINT RELEASE TO THEIR COCKPIT PRINTER. IT WASN'T UNTIL ABOUT 1 HR LATER DID I REALIZE THAT I ERRED BY NOT FOLLOWING THE FULL TEXT OF THE MEL. THE MEL REQUIRES THAT THE PACK PCV BE MANUALLY CLOSED AND DEACTIVATED. ACFT DEPARTED ZZZZ AND WAS HEADED TO ZZZZ1. MAINT IN ZZZZ1 WAS NOTIFIED TO COMPLY WITH THE MEL. MY JOB ENTAILS ME TO WORK AS A RELIEF MAINT CTLR. THOUGH I AM QUALIFIED TO WORK THE B747 FLEET; I HAVEN'T HAD MUCH OF AN OPPORTUNITY TO DO SO; BECAUSE THIS FLEET IS NORMALLY HANDLED BY OUR COUNTERPARTS IN ZZZZ2. ALSO; HAVING THE OPPORTUNITY TO WORK THE OTHER FLEETS; NORMALLY WITH AN INOP PACK THAT IS NOT PUTTING OUT AIR; THE MEL REQUIREMENTS IS TO SELECT THE PACK SWITCH OFF. THIS IS TRUE FOR THE B777; B767; B757; B737; A320; A319. OF COURSE IF THE PCV IS STUCK OPEN; THERE ARE SEPARATE MEL'S FOR THAT SIT. IN HINDSIGHT; I MADE AN ERRONEOUS ASSUMPTION THAT THE SIT I ENCOUNTERED AND THE MEL I APPLIED WOULD NOT REQUIRE ANYTHING MORE THAN SELECTING THE #3 PACK SWITCH OFF; JUST LIKE THE OTHER FLEETS I DEAL WITH. THE ACFT SHOULD HAVE RETURNED TO THE GATE FOR MAINT IN ZZZZ TO DEACTIVATE THE PACK VALVE.