A P180 CREW FLYING A GPS APCH TO CMA GOT TOO LOW AND RECEIVED AN EGPWS WARNING.

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WE WERE FLYING THE GPS 26 CMA APCH. PER OUR USUAL PROCS WE BRIEFED THE APCH. I HAD NOT DONE AN APCH TO CMA BEFORE BUT HAD BEEN THERE MANY TIMES. MY COPLT SAID HE HAD DONE THE VOR AND IT WAS LESS DESIRABLE THAN THE GPS. WE ELECTED THE GPS WX MINIMUMS WERE AROUND 2000 FT CEILING SO IT SHOULD BE NO PROB. WE HAVE ELECTRONIC FLT BAGS (APPROX 11 INCHES BY 8 1/2 INCHES BY 2 INCHES AND ABOUT 3 LBS) SO WE DID NOT HAVE A CHART IN FRONT OF US. WE BOTH MADE OUR OWN APCH NOTES ON PAPER I REBRIEFED. YOU CAN'T FUNCTION WITH THE EFB'S IN YOUR HANDS; THEY'RE TOO HVY AND AWKWARD. THE VECTORS AND ALT WERE POOR WITH A LATE HDOF. THE COPLT WAS FLYING AND DOING A GOOD JOB. HE QUICKENED THE DSCNT AND CALLED FOR THE STEPDOWN ALT TO BE PUT IN THE ALT PRESELECT. I DID THIS -- BIG MISTAKE. I SHOULD HAVE PUT IN ALT AT FAF. MANY ELEMENTS CONSPIRED AGAINST US -- POOR VECTORING; HIGH INITIAL ALT ON COURSE INTERCEPT; NO CHART IN FRONT OF US AND 2 TYPES OF SHORTHAND. WE BROKE OUT OF THE CLOUDS AS THE EGPWS WENT OFF. I SAW THE HILLS; REALIZED OUR MISTAKE AND THE COPLT ARRESTED THE DSCNT. THE ERROR CHAIN WAS BROKEN WITHOUT US BECOMING ANOTHER CFIT ACCIDENT. I AM CONTINUALLY STRIVING TO FIND NEW WAYS TO COPE WITH THESE HUGE; CUMBERSOME NOT USER FRIENDLY EFB'S. EACH NEAR MISS BRINGS HOME THE FACT THAT THEY ARE VERY DANGEROUS. IN A 2 PLT CREW; 1 BECOMES A COMPUTER PROGRAMMER AND THE OTHER IS BACK TO SINGLE PLT WITH LITTLE SITUATIONAL AWARENESS. I WILL ADD CMA TO MY LIST OF PAPER CHARTS I PRINT OUT TO CARRY.