Aerosucre flight 142, a Boeing 727 cargo plane, departed Bogot  at 19:35 hours local time on a flight to Leticia, Colombia. The aircraft carried 13166 kg of cargo, a crew of three and three passengers. Flight time was estimated to be 1 hour and 35 minutes. While en route at FL270, the crew requested weather information for Leticia. A weather report from 01:00Z showed: wind calm, visibility 10 km, scattered clouds at 1000 feet, temperature 24 deg C. The flight descended towards Leticia and was cleared for a straight in approach to runway 21. The air traffic controller instructed the flight to report at 3000 feet. At 20:59 the controller reported that visibility had decreased to 4000 m due to patches of fog. Six minutes later the flight reported at 3000 feet, 9 miles from the airport. The crew requested an increase of the intensity of the runway lights, since there were no approach lights for runway 21. The approach was continued and the flight was cleared to land. The aircraft descended until it impacted a 150-feet high transmission tower. It then hit trees and broke up. PROBABLE CAUSE Performing a flight under instrument conditions attempts to make an approach and landing under visual flight conditions without meeting the minimum requirements for this type of operation. Performing a visual approach with reduced visibility for a runway without instrument approach procedure, which led to flying below safety minima and having descended to hit a transmission tower of private television channels. The poorly planned approach and inadequate IFR operation that led to an erroneous judgement of the obstacle clearance margin. The crew’s inability to circumvent the obstacle on the ground by encountering unforeseen circumstances beyond their capacity.