What happened
On November 17, 1992, an EMB 121 A operated by the Government of Minas Gerais departed Araxá, Brazil, bound for Belo Horizonte. Shortly after takeoff, the crew noticed that the aircraft's pressurization system had failed to engage.
In an attempt to resolve the issue, the co-pilot left his seat to inspect the main door's closing lever. While attempting to force the latch, the door opened abruptly. During the movement, the door's steel support cable tightened, resulting in the amputation of the co-pilot's left hand. The commander immediately initiated an emergency return to Araxá, landing the aircraft with the main door still open. The co-pilot received initial medical aid at the airfield before being transported to a hospital in São Paulo, where the hand was successfully reattached.
The investigation
CENIPA investigators examined the aircraft's maintenance history and the operational environment of the crew. The investigation revealed that the pressurization system had been experiencing intermittent failures since at least August 1992, with no clear record of effective corrective maintenance being performed.
Technical testing of the aircraft found that a locknut on the adjustable screw of the pressurization valve selector had come loose. This allowed the screw to move, resulting in a marginal adjustment that prevented the valve from properly inflating the door seal.
Furthermore, the investigation looked into the crew's operational procedures. It was noted that the pilot's manual specifically prohibits crew members from attempting to correct door malfunctions while in flight and mandates seeking a compatible flight level instead. The investigation also identified a strained relationship between the flight crew and their supervisor, a military police officer, which hindered effective technical oversight and communication.