Flight 1634 · McDonnell Douglas MD-88

The air carrier airplane experienced severe vibrations and a loss of right engine power following a partial loss of 4th stage turbine blades during the takeoff sequence. According to the flight crew's statements, they noticed the vibration and loss of hydraulic fluid quantity and pressure shortly after VR. They then observed a loss of right engine pressure ratio (EPR) and the right engine thrust reverser indication lights. The flight crew reduced right engine power and landed uneventfully at the departure airport. The post-incident examination of the right engine revealed the engine event was caused by the imbalance of the low pressure turbine (LPT) rotor due to a significant loss of the 4th stage blade airfoil and shroud material. This imbalance resulted in rub between the LPT shaft and the high pressure turbine (HPT) shaft. A hole was eventually rubbed through the LPT shaft. Oil in the vicinity of this shaft rub was ignited, giving the LPT shaft the appearance of burn through. The extent of the damage to other systems (hydraulic lines, EPR reference lines, fire warning systems, etc.) was attributed to the duration of excessive vibration experienced until the engine was safely shutdown. Prior to the incident, the right engine was placed on a 50-cycle continue-in-service limitation in accordance with a P&W internal engineering notice for missing 4th stage turbine blade shroud/shrouds. At the time of the event, the right engine had accumulated 13 cycles of the 50-cycle limit. The post-incident blade material loss observed was well above that allowed under the continue-in-service limits, and the imbalance was most likely the result of another event that occurred after the continue-in-service shroud inspection. The cause of the 4th stage material loss could not be conclusively determined.

Verbatim NTSB analysis and probable cause from the NTSB dataset