ALTDEV BY A MULTI-ENG TRAINEE.

Narrative

THIS FLT WAS A TRAINEE'S MULTI-ENG COURSE PROGRESS CHK. THE TRAINEE CTLED THE AIRPLANE IN THE L SEAT AND I TOOK THE R SEAT AS THE CHK PLT. AFTER COMPLETING SOME VFR TOUCH AND GOES WE DEPARTED SMF TO NAPA COUNTY ARPT VFR. WHEN WE CONTACTED SAC DEP CTL WITH OUR REQUEST TO CLB TO 6500 FT VFR; THE CTLR GAVE US A CLRNC TO MAINTAIN 3500 FT DUE TO TFC COMING TOWARD US FROM THE 10 O'CLOCK POS AT 4000 FT. MY TRAINEE ACKNOWLEDGED TO MAINTAIN 3500 FT. THE CTLR ALSO GAVE ANOTHER ACFT SOME TFC INFO THAT WAS SPOKEN VERY FAST. THE TRAINEE DID NOT UNDERSTAND IT VERY WELL. THINKING THE INFO WAS FOR HIM HE REQUESTED TO 'SAY AGAIN' EXPECTING THE CTLR TO SAY IT A LITTLE SLOWER; WHICH HE DID NOT. THE TRAINEE ANSWERED WITH 'ACFT NUMBER ROGER;' WITHOUT UNDERSTANDING THE INSTRUCTIONS. THIS CAUSED HIM TO BECOME TEMPORARILY DISTR BY ATC AND HE WAS NOT FOCUSING ON HIS ALT. HE WAS LOWERING THE PITCH ATTITUDE TO LEVEL OFF AT 3500 FT; BUT I REALIZED THE AIRPLANE WAS STILL SLOWLY GAINING ALT. AT THIS TIME THE TRAINEE IN THE BACK SEAT NOTICED THE 10 O'CLOCK TFC MLG ACFT NOW AT OUR 8 O'CLOCK POS ABOUT 2-3 MI AWAY. I COULD NOT SEE THE TFC FROM MY SEAT SO I CONTINUED TO LOOK FOR THE TFC TO CONFIRM HIS POS. WHILE I WAS LOOKING FOR THE TFC I WAS NOT SCANNING THE ALTIMETER AND SUDDENLY I NOTICED OUR AIRPLANE HAD CLBED TO 3950 FT! AT THE SAME TIME THE CTLR ADVISED US OF OUR ALTDEV. WE WERE INSTRUCTED TO TELEPHONE ATC REGARDING OUR ALTDEV UPON LNDG AT OUR DEST. MY REFLECTION: ONCE I REALIZED WE WERE DEVIATING FROM THE ASSIGNED ALT I DID NOT FIRMLY ADVISE THE TRAINEE TO MAINTAIN 3500 FT. I SHOULD HAVE TAKEN OVER CTL OF THE AIRPLANE AND LEVELED OFF APPROPRIATELY. I PAID TOO MUCH ATTN TO THE OUTSIDE TFC AND THEREFORE WAS TOO LATE IN REALIZING OUR ALTDEV; AND I HAD A LITTLE TOO MUCH CONFIDENCE IN THE TRAINEE'S SKILL.