The aircraft had departed Palembang 80 minutes earlier and had been cleared for an approach to runway 05 at Medan Airport. The aircraft was asked to report passing the nondirectional beacon (NDB) "ON" at 2,500 feet (760 m). The pilot then reported he was maintaining a height of 9,300 feet (2,800 m) as the NDB was unreliable. The approach controller then asked them to maintain that height until after they had passed the NDB. The pilot then reported they were at 6,000 feet (1,800 m). The aircraft struck the 7,200-foot-high (2,200 m) volcano Mount Sibayak at 5,560 feet (1,690 m).[1]