BE90 PLT HAD ALT AND TRACK DEV WHILE ATTEMPTING TO REPROGRAM THE ACFT FMC IN IMC TURBULENT CONDITIONS IN N90 CLASS B.

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LIKE ALL INCIDENTS; A SERIES OF CIRCUMSTANCES LED TO A SIT THAT; UNDER DIFFERENT CIRCUMSTANCES; COULD HAVE BEEN POTENTIALLY DANGEROUS. THIS PARTICULAR INCIDENT WAS NOT DANGEROUS BECAUSE IT DID NOT OCCUR IN CLOSE PROX OF OTHER ACFT OR TERRESTRIAL OBSTACLES AND I MAINTAINED CTL OF THE ACFT AT ALL TIMES. DEPARTING TEB IFR; NEW YORK DEP CTL AMENDED MY CLRNC TO INTERCEPT THE COLTS NECK 350 DEG RADIAL. PARTLY BECAUSE OF THE DISTRACTIONS OF IMC CONDITIONS AND TURB; I MISTAKENLY ENTERED '350' RATHER THAN '170' INTO MY EFIS'S HSI. AS A RESULT; I TURNED R RATHER THAN L. THE CTLR CAUGHT MY ERROR AND DIRECTED A CORRECT TURN. WHILE I WAS SIMULTANEOUSLY TURNING AND REPROGRAMMING MY EFIS; WE ENCOUNTERED A DOWNDRAFT THAT WAS SO STRONG THAT IT DISENGAGED THE AUTOPLT. AS A RESULT; THE PLANE LOST ALT AND THE ACFT DSNDED BELOW MY ASSIGNED ALT OF 5000 FT. REFLECTING ON THESE SERIES OF EVENTS; I FEEL THAT SINGLE PLT OPERATORS SHOULD DEVELOP A PROC FOR USING THEIR EFIS IN ITS SIMPLEST; MOST INTUITIVE MODE AND/OR BACK IT UP USING LESS COMPLEX NAV SYS. AT THE TIME OF THIS INCIDENT; I HAD MY INITIAL CLRNC'S FIRST GPS WAYPOINT (WHITE INTXN) AND THE COLTS NECK VOR PROGRAMMED AND SIMULTANEOUSLY DISPLAYED. IN THE FUTURE; RATHER THAN HAVING MULTIPLE OVERLAYS PROGRAMMED INTO MY EFIS'S HSI; I WILL PROGRAM ONLY ONE. ALSO; I WILL SET MY COPLT HSI (WHICH IS ANALOG) TO THE PRIMARY NAV FIX. ALTHOUGH EFIS SYS ARE WONDERFUL; THEIR ABILITY TO DISPLAY VAST AMOUNTS OF INFO AND THEIR SLOWER; MORE COMPLEX AND OFTEN DISTRACTING PROGRAMMING REQUIREMENTS CAN CREATE PROBS PARTICULARLY IN SINGLE PLT; HIGH WORKLOAD; IMC AND UNFAMILIAR ENVIRONMENTS. THEREFORE; I WOULD SUGGEST THAT PLTS BE TRAINED ON HOW TO USE THIS EQUIP IN ITS SIMPLEST WAY. HAVING ATTENDED REGULARLY FOR 8 YRS; I DO NOT RECALL EVER BEING TRAINED ON THE SIMPLE USE OF SOPHISTICATED EQUIP. THE FOCUS ALWAYS SEEMS TO BE ON ITS MOST COMPLEX USE.