MAP SHIFT ON IRS EQUIPPED B-757.

Narrative

DEPARTED SYR FOR SDF XA28 LCL. DURING CLB; NOTICED LARGE MAP SHIFT ON EHSI. BECAUSE WE NORMALLY NAV SOLELY USING IRS DATA; WE ELECTED TO TRY TO GET IRSS BACK UP TO SPD. SELECTED ATTITUDE ON IRS CTL PANEL AND; AS A RESULT; LOST AUTOPLTS; AUTOTHROTTLES; FLT DIRECTORS; AND HAD QUESTIONABLE GUIDANCE FROM AIR DATA DRIVEN INSTS. SHORTLY AFTER THIS WE WERE GIVEN A CLBING TURN. DURING THE CLB; THE ALTIMETER INDICATED A CLB AND THE VSI INDICATED A DSCNT. WE THEN REALIZED THAT WE WERE DOWN TO THE STANDBY INSTS. ONLY PROB BEING THE CAPT'S ALTIMETER SEEMS TO DRIVE THE SIGNAL SENT BY THE MODE C XPONDER. WE ADVISED ATC OF THE EQUIPMENT FAILURES AND CHKED THEIR ALT AGAINST OURS. THEY SHOWED US 400 FT HIGH; NO TFC CONFLICT. FLT CONTINUED UNEVENTFULLY. WE FOUND NO GUIDANCE FOR OUR NAV PROB IN OUR QUICK REF CHKLIST. IF WE COULD HAVE READ ABOUT THIS SYS; WE WOULD NOT HAVE SELECTED ATTITUDE POS ON IRS. SUPPLEMENTAL INFO FROM ACN 286775: DUE TO A SELF- INDUCED NAV PROB OUR BOEING 757 LOST ALL COMPUTER GENERATED NAV SYS AND AIR DATA COMPUTER INPUTS TO THE CAPT'S ALTIMETER. THE CAPT'S ALTIMETER GIVES PRIMARY INFO TO ATC. AT ONE POINT IN THE FLT; WE WERE OFF OUR ASSIGNED ALT 400 FT. WE WERE ACTUALLY AT THE CORRECT FLT LEVEL; BUT THE RPTING ALTIMETER WAS INCORRECT.