A NEAR ALT BUST IS RPTED BY PLT WHO MISREAD INST DURING PLT TECHNIQUE PREFLT INSPECTION PROC.

Narrative

OUR SINGLE PLT CITATION HAD BEEN IN MAINT FOR A FEW DAYS WHILE A NUMBER OF SMALL PROBS WERE BEING ADDRESSED; INCLUDING THE REPLACEMENT OF THE NUMBER 1 XPONDER (A LOANER) WITH OUR REPAIRED UNIT. UPON DEP FROM DEN WE CHKED ON WITH DEP WITH OUR CURRENT ALT AND OUR ASSIGNED ALT OF 10000 FT. PASSING THROUGH 8000 FT WE WERE GIVEN A HDG TO FLY TO JOIN J80. AS WE STARTED THE TURN IT WAS NOTED THAT THE COPLTS SET OF INSTS SHOWED US TO BE 1000 FT BELOW THE ALT DISPLAYED ON THE PLTS INSTS. A COUPLE MOMENTS OF XCHKING REVEALED THAT THE PLTS ALTIMETER WAS SET TO THE WRONG ALTIMETER SETTING. THE ALT PRESELECT WAS DISENGAGED AND THE ACFT LEVELED AT 10000 FT IN REF TO THE COPLTS ALTIMETER WHILE THE PLTS ALTIMETER WAS RESET TO THE PROPER SETTING. ATC QUERIED US AS TO OUR ALT WHICH THEY SAID SHOWED US TO BE 400 FT HIGH. WE VERIFIED THAT WE WERE AT 10000 FT BUT DUE TO THE WORKLOAD DID NOT FURTHER EXPLAIN OUR SIT. A FEW MOMENTS LATER AS WE JOINED J80 OUR #1 XPONDER FAILED. I BELIEVE THAT THE PLT'S ALTIMETER MAY HAVE BEEN RESET DURING THE TESTING OF THE REPAIRED XPONDER. THIS MAY HAVE LEFT THE ALTIMETER CLOSER TO BEING RESET TO 1000 FT ABOVE THE FIELD ELEVATION. THE APCH OF A STRONG LOW PRESSURE AREA THAT DAY MAY HAVE CONTRIBUTED TO THIS RESETTING OF THE ALTIMETER TO THE WRONG SETTING. MORE IMPORTANTLY THE PLTS INSTS SHOULD HAVE BEEN XCHKED MORE CLOSELY TO THE COPLTS. THIS ACFT WAS BEING OPERATED AS A SINGLE PLT OP AND IN THE PAST IF THE ALTIMETER READ THE FIELD ELEVATION THEN NO FURTHER CHKING WAS ACCOMPLISHED. IN THIS CASE THE ALTIMETER WAS MIS-SET AND THEN MIS-READ ON THE GND. WHEN ONE MAKES A MISTAKE SETTING AN INST THE CHANCES ARE THEY WILL MIS- READ IT AGAIN WHEN XCHKING IT. OUR COMPANY POLICY HAS BEEN CHANGED TO INCLUDE A COPLT ON ALL POSSIBLE FLTS TO PREVENT SOMETHING OF THIS NATURE FROM HAPPENING AGAIN.