What happened
On December 26, 1999, a Douglas DC9-83 operating a charter flight to Las Palmas attempted to take off from runway 26L at Munich Airport. As the aircraft reached rotation speed (VR), the pilot was unable to initiate rotation. The control column would only move slightly past the neutral position, preventing the necessary pitch-up maneuver. The pilot immediately performed an aborted takeoff, which was completed successfully due to the available runway length. There were no injuries to the crew, though the aircraft sustained minor damage.
The investigation
The BFU investigation focused on the mechanical state of the elevator control system, which consists of an elevator, a control tab, and a mechanical-hydraulic actuation system. The investigation established that the aircraft had been diverted to Munich earlier that day and had been parked at the gate during a period of severe weather. Between 14:20 and 16:20, the aircraft was exposed to gusty tailwinds reaching up to 70 knots.
During the investigation, it was found that the flight data recorder (FDR) was unavailable. Investigators examined the mechanical linkages of the geared tab (G-TAB) and the elevator. They discovered that the left elevator was blocked in a downward position because an internal linkage had become wedged against the structure. This condition was caused by the elevator exceeding its normal travel limits, which overstressed the spring-loaded stops.
Findings
- The primary cause of the incident was the failure to detect a blocked elevator control system during pre-flight and taxi inspections.
- Extreme tailwinds of up to 70 knots caused the elevator surfaces to be slammed against their mechanical stops, forcing the internal linkage into a jammed position.
- The pilot-in-command (PIC) performed a functional check at the gate after observing the wind's effect on the control surfaces, but the check was incomplete. The heavy movement of the controls and the lack of the hydraulic power indicator (ELV-PWR-ON) were noted, but these symptoms were dismissed as normal operating characteristics for the Douglas DC9-83.
- During the taxi checklist, the pilot noted a delay in the hydraulic indicator light, but did not pull the control column to its full rearward limit, which would have revealed the blockage.
- Maintenance and operational procedures were insufficient; the Aircraft Maintenance Manual (AMM) lacked specific instructions for inspections following exposure to winds exceeding 65 knots, and the pilot was unaware of the specific risks posed by such high tailwind components.
Safety action
- The BFU issued recommendations to update the Airplane Flight Manual (AFM) to include warnings that the elevator can block and that a full control surface inspection is required if the aircraft is parked with tailwinds exceeding 65 knots.
- Recommendations were made to update checklists to ensure the control column is pulled to its full rearward limit during taxi checks to verify control freedom.
- The BFU recommended that the AMM include specific instructions for inspections following exposure to winds over 65 knots.