B747 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Flight Crew Overcame Equipment Problem; Flight Crew Returned To Clearance
Aircraft
On approach; using STAR arrival. Flight was normal; descending via the STAR. We were on Vnav Path all the time; until Vnav jumped around 6000 ft showing us above the path. At this time we saw the runway and extended flaps 20; gear down; speed brakes up; slow down to normal speed; reported runway in sight; and were trying to make stable approach until we reach 500 ft and; if unable; to go around. We made S-turns and descent in normal parameters. Landing was made well within landing parameters.We had [an] MEL on the Right Auxiliary Pitot Static probe heater inoperative which affected the Center ADC and possibly could cause unreliable AIS or altitude which in our situation contributed to unreliable Vnav Path condition.
B747 Captain reported that while descending on a STAR in VNAV mode; the VNAV abruptly reset 6;000 feet lower. A stabilized approach and uneventful landing were made despite the high; in-close position. An MEL on the Right Auxiliary Pitot Static Probe Heater may have been a factor as the Center ADC was affected.