Safety News

Redesign Called for on DC-8: For want of proper maintenance, the retaining bolt was improperly installed. For want of the bolt, the elevator jammed. For want of redundancy, the pilots lost pitch control. For want of control, the airplane crashed.

While the proximate cause of the fatal February 16, 2000, crash of an Emery Worldwide Airlines DC-8 freighter may track to actions not taken on the hangar floor, the ultimate cause links back to the design floor.

In terms of a "single point failure," the accident is an important case study. The National Transportation Safety Board concluded its investigation into the crash of Emery Flight 17 with a battery of recommendations for improved maintenance. Also contained in the numerous recommendations is a call to retrofit all DC-8s with a more redundant flight control system. Such a mandate would affect 110 DC-8s in U.S. registered service (148 others are in service worldwide and 72 are stored).

Investigators first thought the crash of the Emery freighter was caused by an out-of-balance condition, as the flight crew reported such in their last radio transmission to air traffic control. But when it became evident that the Emery jet was within its weight and balance limits, investigators dug deeper. Anomalies in the elevator position during the doomed airplane's brief flight pointed to a control problem.

The elevator control system underwent maintenance when the accident airplane was overhauled in November 1999. This D check was performed by Tennessee Technical Services of Smyrna, Tennessee, which was doing the work on contract to Emery. During the course of this work, the elevator assemblies were removed.

Eight days after the D check was completed, pilots reported that the elevators seemed stiff, requiring more back pressure to flare the aircraft on landing. Emery technicians found the elevator dampers had been reversed during the course of the work at Tennessee Tech. However, placing the dampers in their proper position would have had no effect in alleviating the control stiffness reported by pilots, NTSB investigator-in-charge Frank Hildrup said at the board hearing.

The area of interest was on the right side, where the control rod and tab fitting were found, but not the bolt connecting the two. Sources say the nut was found inside the elevator. The consequence of a bolt falling out of position would be significant. It could happen if put in backwards, without a cotter pin. As Hildrup explained, a disconnected pushrod could slide over the face of the left bracket on the tab fitting, "blocking the tab in the extreme down position." Indeed, score marks on the fitting suggest contact damage from a loose pushrod banging against the fittings.

The bolt fell out of its proper position either by the bump of touchdown on landing of the previous flight or it slipped out during the flight control checks.