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In the flight preceding 592, the aircraft's cabin announcement system was not working properly and flight attendants used a handheld loudspeaker to make announcements to passengers. On 592, the flight attendents had no communication with the flight deck (cockpit) other than knocking or shouting through the cockpit door. The NTSB says that this is acceptable as long as the cabin crew and pilots have an agreed system of communication as an alternative to using the intercom. The extent of the information that the flight crew had was hearing "fire, fire, fire," being shouted from the cabin.
Although ValuJet caused many factors in the crash and the final straw was unrelated to the mechanical operations of the aircraft, ValuJet was negligent in allowing that aircraft to fly. Additionally, the ValuJet manuals do not have the Douglas DC-9 Flightcrew emergency procedure for removing smoke from the cabin during flight. Northwest Airlines, US Airways, and Midwest Express Airlines DC-9 pilot's handbook include this procedure
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The aircraft was not airworthy. It's no doubt that ST incorrectly marked the canisters as empty. However, ValuJet was incapable of handling the cargo, incapable of responding to the fire, and in especially poor shape given the condition of the aircraft.