Narrative:

Had achieved our planned and programmed cruise altitude of FL350. Given clearance to cross zzzzz at 11;000 ft; at that time we're at FL200 and just over 30 miles from zzzzz. The captain (pilot flying) commenced a standard 3 degree descent with the vpi (vertical path indicator) centered. During the descent the vpi showed the aircraft descending below the desired 3 degree path; the PF adjusted the rate of descent accordingly. About 5 miles from zzzzz; with the vpi showing the aircraft well below the 3 degree path (and thus ahead of the required descent performance); the PF determined the vpi had slowly drifted (very insidious) and was lying to the flight crew. The aircraft was actually well above the required descent path (and thus behind in the required descent performance). The PF increased the rate of descent significantly but still crossed zzzzz at 13;500 ft. TCAS didn't show any traffic in the area.the vpi now is the threat; and opposed to being an aide to flight crews. It seems no two situations involving the vpi's failure to perform are alike; making it impossible for flight crews to plan ahead. The vpi system needs to be thoroughly investigated for the cause of these insidious failures. This crew was at altitude and the vpi falsely indicated we were lower than planned. The next time the vpi insidiously drifts like this; it could falsely indicate to a flight crew; that they are higher than planned on an RNAV approach to minimums. This could result in a terrain avoidance event.

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Original NASA ASRS Text

Title: EMB-145 Captain reported the Vertical Path Indicator on descent showed the aircraft well below the desired flight path when it was actually well above. Captain reported that no VPI failure situations are alike and is concerned the system could show the aircraft higher than it actually is.

Narrative: Had achieved our planned and programmed cruise altitude of FL350. Given clearance to cross ZZZZZ at 11;000 ft; at that time we're at FL200 and just over 30 miles from ZZZZZ. The Captain (Pilot Flying) commenced a standard 3 degree descent with the VPI (Vertical Path Indicator) centered. During the descent the VPI showed the aircraft descending below the desired 3 degree path; the PF adjusted the rate of descent accordingly. About 5 miles from ZZZZZ; with the VPI showing the aircraft WELL BELOW the 3 degree path (and thus ahead of the required descent performance); the PF determined the VPI had slowly drifted (very insidious) and was lying to the flight crew. The aircraft was actually WELL ABOVE the required descent path (and thus behind in the required descent performance). The PF increased the rate of descent significantly but still crossed ZZZZZ at 13;500 ft. TCAS didn't show any traffic in the area.The VPI now is the THREAT; and opposed to being an aide to flight crews. It seems no two situations involving the VPI's failure to perform are alike; making it impossible for flight crews to plan ahead. The VPI system needs to be thoroughly investigated for the cause of these insidious failures. This crew was at altitude and the VPI falsely indicated we were LOWER than planned. The next time the VPI insidiously drifts like this; it could falsely indicate to a flight crew; that they are HIGHER THAN PLANNED on an RNAV approach to minimums. This could result in a TERRAIN AVOIDANCE EVENT.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.