Flight GUG901 (Miami-Guatemala City-San Salvador-Managua-San Jose) encountered bad weather (heavy rain, thunderstorms) while approaching San Salvador. The crew therefore diverted off Airway G346 to avoid the thunderstorms. The aircraft should then have passed overhead the airport and turn right downwind for an ILS approach to runway 07. There seemed to be some confusion as to the position of the aircraft. The aircraft was at 5000 feet (as cleared by ATC) when the GPWS sounded. Full power was applied, but the Boeing struck the San Vicente Volcano (also known as Chinchontepec, 2181 m high) at an altitude of 1800 m. PROBABLE CAUSE: “The Direccion General De Transporte Aereo determines that the probable cause of the accident was the flight crew’s lack of situational awareness in relation to the 7,159 foot obstruction, the flight crew’s decision to descend below the MSA while deviating from a published transition or approach, and the ambiguity of position information between both the flight crew and the air traffic controller which resulted in the controller’s issuance of an altitude assignment that did not provide terrain clearance. Contributing to the accident was the failure of the First Officer to direct his concern of reported positions to the Captain in a more direct and assertive manner and the failure of the controller to recognize the aircraft’s reported position relative to obstructions and give appropriate instructions/warnings. An ineffective CRM program at Aviateca also contributed to the accident .”