During a regular flight between Araracuara (SKAC) and Florencia (SKFL), the crew of the Y-12E aircraft encountered cumulonimbus clouds. The crew decided to cross the formation, assuming they would only experience light turbulence; however, the effect of the turbulence caused the aircraft to descend 5500 ft uncontrolled, in a few seconds, to an altitude of 5000 ft. The crew regained control, and landed without further problems at 16:09. As a result of the event, one passenger suffered minor injuries. Due to the cumulonimbus crossing the aircraft suffered severe structural damage. The investigation determined that the probable cause of the accident was loss of situational awareness (SAW) and decision-making ability (ADM) on the part of the Commander, who failed to prevent the flight from crossing through a severe weather condition (cumulonimbus), despite having warned of this hazard and having been detected and clearly identified on the weather radar. As contributing factors were found: – A reckless attitude of the crew in underestimating a clearly detected and recognized weather hazard and in boasting of their ability to fly through those conditions – Poor management of resources in the cockpit, by not using the right tools such as leadership, assertive communication and proper decision making based on risk assessment. – And, finally, complacency on the part of the First Officer as a Pilot Flying, who executed the Commander’s orders without considering the risk or consequences of entering into known bad weather conditions.