The US National Transportation Safety Board (NTSB) today said the July 2008 diversion of a Midwest Airlines charter flight with Presidential candidate Barack Obama onboard was triggered by a partial inflation of an emergency slide located in the MD-81's tailcone whose cover was not properly secured.

NTSB explains the slide inflated shortly after takeoff from Chicago. The aircraft was bound for Charlotte, North Carolina but diverted to St. Louis after the pilots determined during initial climb that the aircraft's pitch increased and exceeded normal limits without a corresponding flight control input.

Although the crew regained control of the aircraft a significant restriction in pitch control still remained.

The partial deployment of the evacuation slide was discovered during a post-incident inspection, and the pitch control restriction was caused by the inflated slide and a subsequently damaged walkway railing impinging on a set of elevator cables in the tailcone.

In its final incident report released today NTSB explains a properly secured slide cover would have contained the slide if the inflation cylinder improperly discharged. Testing conducted after the incident did not reveal any anomalies that would have resulted in an unintentional discharge of the cylinder for other reasons. Additional tests also showed that the slide pack could not have rotated enough to activate the inflation cylinder if the slide container was properly secured.

"It could not be determined why the slide's cover was not secured," states NTSB. "In normal circumstances, the cover is secured by the mechanic who installs it and should remain secured until it is removed from the airplane."

Deployed slide-obama 
 Partial deployment of the evacuation slide was discovered during a post-incident inspection

A service check of the incident aircraft's tailcone was completed on 5 June 2008 with no anomalies detected. That check was a visual examination of numerous items in the cabin including forward tie-down straps to secure the slide cover, and NTSB highlights a mechanic would have no reason to touch the straps during the examination. The board also explains a 20 June 2008 inspection of the tailcone's slide inflation bottle pressure did not specifically require examining the straps.

NTSB says shortly after the incident Midwest issued a maintenance alert bulletin describing the incident and the initial findings from the ensuing investigation. Midwest also released a revised check work card that included specific language calling for maintenance personnel to examine tie-down straps to verify proper installation and security during reoccurring service checks.

The board says only two other previous incidents of inadvertent tailcone inflation in MD-80 series aircraft have been reported, and the causes of each inflation could not be definitively determined.

Source: Air Transport Intelligence news