While on final approach, the autopilot automatically disconnected. The Captain proceeded to reengage it, believing that it would still be in APP mode. When activated however, the autopilot went into VERT SPD mode with a setting of -800 feet per minute. The crew's failure to disconnect the autopilot and manually land the airplane contributed to the accident. Another factor was the crew's lack of proficiency in English. When the GPWS issued an aural alarm, the captain asked his first officer what the words "Pull up" meant. The first officer replied that he did not know. Consequently, the pilots ignored the warnings and failed to correct their excessive rate of descent, causing the plane to strike power lines and a wall before coming down in a field.