Air Tran Airways Flight 356

The Boeing 717 was on final approach when the display units (DUs) in the cockpit blanked, and the cockpit darkened. In addition smoke was smelled in the cockpit, and cabin. In the cabin, the emergency light illuminated for a few minutes, and then all lights extinguished and the cabin was dark. The landing gear was lowered. When the wing flaps were positioned to 40 degrees, a landing gear aural warning commenced and continued until power was removed after landing. The captain reported when the event initiated, he directed his vision outside the cockpit where it remained until after landing. The co-pilot reported that he also directed his vision outside of the cockpit in the final 20 seconds of approach. Neither pilot made use of the standby instruments or used a flashlight to check instruments. The captain commanded an emergency evacuation after he cleared the runway and stopped. When interviewed, the flight attendants reported that during the emergency evacuation, they did not check conditions outside of their doors prior to opening them. In addition, cabin emergency lighting was not turned on by the flight attendants, and the flight attendant at the tail cone station was unable to deploy her slide. Examination of the airplane revealed the left power control distribution unit (PCDU) had failed. The left DC bus was also lost and the ability to power the left DC bus from other sources was also lost. The failure of the PCDU was not instantaneous and it tried to recycle several times. Each time the PCDU recycled, it also reset the display of new data on the remaining DUs. This caused an extended blank display followed by eventual reset of data. The pre-programmed response to the loss of the left DC bus was the loss of two DUs, one on each side of the cockpit.

Verbatim NTSB analysis and probable cause from the NTSB dataset