ERROR ADMITTED; AN ACR B757 CREW MISPROGRAMMED ITS FMC AND WERE UNABLE TO FLY A SID PROPERLY. THIS RESULTED IN A TRACK DEV.

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WE WERE TO DO THE PEARSON 5 DEP OFF OF RWY 24R IN YYZ. THE SID CALLED FOR GOING DIRECT TO MOBEM INTXN. DURING THE PREFLT; THE CAPT ASKED ME HOW HE WOULD ENTER MOBEM INTO THE FMC; BECAUSE IT WAS NOT IN THE DATABASE. I TOLD HIM HE COULD ENTER THE LATITUDE/LONGITUDE OR THE 240 DEG RADIAL/3.9 DME FIX. HE SAID HE WOULD ENTER THE 240 DEG/3.9 DME AND PROCEEDED TO DO SO. AFTER DEP; THE ACFT BEGAN A 30 DEG TURN TO THE L USING LNAV. I SAID THIS CANNOT BE RIGHT; CALLED FOR HDG SELECT AND WENT BACK TO A 240 DEG HDG AND THEN DIRECT GADKA. TORONTO DEP SAID THAT THEY NOTICED THE TURN; AND ASKED IF WE COULD EXPLAIN WHY; BECAUSE THIS WAS A NEW DEP AND THEY HAVE NOTICED MANY ACFT DOING THE SAME THING. AT THE TIME; WE HAD NO EXPLANATION FOR THE TURN. WE LATER FIGURED OUT THAT WHEN THE CAPT ENTERED THE 240 DEG/3.9 DME FIX; HE USED TORONTO INSTEAD OF THE PEARSON VOR. HE ASSUMED THAT BECAUSE HE WAS LEAVING TORONTO; TO A FIX 3.9 MI AWAY; IT MUST BE OFF THE TORONTO VOR. I CAN SEE HIS POINT. WHO WOULD THINK THAT 2 VORS WOULD BE ON THE SAME FIELD LESS THAN 1 MI APART? THE ERROR ONLY PUT US LESS THAN 1 MI OFF COURSE. IT COULD HAVE PUT US IN THE RWY 24L DEP RWY. PERHAPS A NOTE COULD BE PUT ON THE SID TO BE AWARE OF THIS POTENTIAL ERROR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR FLIES THE B757. HE STATES THAT THE CAPT PROGRAMMED THE FMC AND THE RPTR THOUGHT THAT IT HAD BEEN DONE CORRECTLY. HE DOES NOT KNOW WHY THERE ARE 2 VORS LOCATED ON TORONTO/PEARSON ARPT; AND DOES NOT REMEMBER THE YTP VOR AS BEING NEWLY INSTALLED. THE TONE OF VOICE OF THE CTLR INDICATED TO THE RPTR THAT THERE MAY HAVE BEEN MANY SIMILAR MISTAKES. AS THIS IS THE 'PEARSON 5' SID; THE PEARSON VOR MUST HAVE BEEN IN SVC FOR SOME TIME. THE RPTR DOES NOT KNOW IF THE SID HAS BEEN PUT INTO HIS ACR'S DATABASE AS HE HAS NOT BEEN BACK INTO YYZ SINCE THIS INCIDENT.