OLD MODEL CPR JET HAD ALTDEV IN TURB WX DEPARTING HPN.

Narrative

I WAS THE PNF OF AN LTT DEPARTING WHITE PLAINS; NY; (HPN) FOR TETERBORO; NJ; (TEB). WHILE FOLLOWING THE STANDARD INST DEP (R TURN TO HDG 320 DEGS; MAINTAIN 3000 FT); DEP CTL SAID OUR ALT VARIED BTWN 3600 FT AND 2800 FT. I STARTED THE DAY OUT BY FLYING THE ACFT FROM TEB TO HPN AND IT BECAME APPARENT REAL QUICK THAT TRUE TO THE WX FORECAST THIS WAS NOT GOING TO BE A FUN DAY. THE WX AT HPN WAS FORECAST TO BE 200-300 FT CEILINGS WITH 1/2 TO 3/4 MI VISIBILITY AND MODERATE TURB ALL DAY. MY ILS APCH INTO HPN WAS TO MINS AND I WAS FIGHTING MODERATE TURB WITH 15 KT AIRSPD FLUCTUATIONS THE WHOLE WAY. ON THE FLT FROM HPN TO YIP WE ENCOUNTERED MODERATE TURB AT ALL ALTS TO FL390. ON THE RETURN TRIP THE OTHER PLT FLEW THE ACFT AND ENCOUNTERED THE SAME WX PROBLEMS THAT I HAD; MODERATE TURB; LOW CEILINGS AND VISIBILITY. WHILE BEING VECTORED TO THE ILS I SUGGESTED TO HIM THAT SINCE WE WERE BOTH TIRED FROM FIGHTING TURB ALL DAY AND KNOWING WHAT IT WAS LIKE GOING INTO HPN EARLIER; WE SHOULD CONFIGURE THE ACFT INTO A WINDSHEAR PROFILE FOR THE APCH. HE AGREED AND MADE A GOOD APCH AND LNDG. WHILE I DEPLANED THE PAX HE PICKED UP THE IFR CLRNC AND WE WERE OFF ON OUR LAST LEG OF THE DAY. WHILE EXECUTING THE STANDARD INST DEP; NY DEP CTL STATED THAT OUR ALT VARIED FROM 3600-2800 FT. I DON'T KNOW WHAT OUR EXACT ALT WAS WITH THE WAY THE ACFT WAS BOUNCING AROUND IN THE TURB AND THE WAY THE ALTIMETERS WERE SWINGING BACK AND FORTH BUT IT APPEARED TO AVERAGE AROUND 3000 FT SO THAT'S WHAT I RPTED AS OUR ALT. ONE OF THE CONTRIBUTING FACTORS TO OUR PROBLEM IS THE STATIC SYS IN OUR 1979 JET. IF YOU GET THIS VINTAGE OF JET INTO A STANDARD 28 DEG BANK TURN OR MAKE A SUDDEN PITCH CHANGE THE ALTIMETERS ARE MOMENTARILY INACCURATE. I HAVE DISCUSSED THIS WITH THE FACTORY AND WAS TOLD I COULD GET THE NEW STYLE STATIC SYS BUT I HAD TO BUY A $200;000.00 AUTOPLT TO GET IT. CONVERSATIONS WITH ENGINEERS HAVE STATED THAT THERE IS NO REASON THE NEW STATIC SYS CAN'T BE SOLD WITHOUT THE NEW AUTOPLT. APPARENTLY IT'S NOT COST EFFECTIVE. IN MY ACFT WITH THE CURRENT STATIC SYS WHICH HAS A STATIC CORRECTION MODULE ON THE PLT'S SIDE ONLY YOU CAN HAVE A 700 FT DIFFERENCE BTWN THE PLTS AND COPLT ALTIMETERS. IF THE COPLT IS FLYING THE ACFT HE HAS TO LOOK OVER TO THE PLT'S INSTS TO SEE WHAT THE ACTUAL ALT IS. THIS IS STUPID AND UNSAFE. HOW AN ACFT LIKE A JET CAN BE CERTIFIED LIKE THIS IS BEYOND ME.