Douglas DC-10-30CF accident at Miami, Florida, 22 Sept 1981 (N101TV)

Accident narrative

On September 22, 1981, at about 1648 e.d.t., Air Florida Airlines Flight 2198, a McDonnell-Douglas DC-10-30CF (N101TV), experienced an uncontained failure of its right underwing engine during the takeoff roll at Miami International Airport in Miami, Florida. The captain rejected the takeoff and stopped the aircraft safely. None of the 71 people aboard were injured.

### The flight

Flight 2198 was a regularly scheduled passenger flight from Miami to Newark, New Jersey, with an en route stop at Fort Lauderdale, Florida. There were 56 passengers and 15 crewmembers aboard.

The captain had 7,100 flight hours, including 800 hours in the DC-10. The first officer had 3,950 flight hours, with 460 in the DC-10, and the flight engineer had 2,200 flight hours, with 500 in the DC-10.

### The sequence of events

The aircraft departed the terminal gate at 1630 and taxied to runway 9L. The computed takeoff speeds were a critical engine failure speed (V1) of 133 KIAS, a rotation speed (VR) of 133 KIAS, and a takeoff safety speed (V2) of 149 KIAS.

At 1647:16, the flight was cleared for takeoff. The airspeed indicators were cross-checked at 80 KIAS with no discrepancies noted. About three seconds later, at about 90 KIAS, the flightcrew heard a noise "like rushing air" followed by a "hollow boom." The aircraft yawed to the right and began to vibrate. The captain corrected the yaw and initiated rejected takeoff procedures by retarding the thrust levers, applying the wheel brakes, and deploying the spoilers. Reverse thrust was not selected because it could have adversely affected directional control.

As the aircraft decelerated through about 60 KIAS, the crew noted the No. 3 engine's N1 indicator read zero, its N2 indicator read 107.5 percent, and its exhaust gas temperature read 657°C. The engine failure light had not illuminated. The first officer shut down the engine. The tower informed the crew that smoke or vapor appeared to be coming from the No. 3 engine, and the flight engineer pulled the fire handle and discharged the extinguishing agent.

The aircraft exited the runway and stopped on a taxiway. Passengers deplaned through the forward left cabin door via portable airstairs. There was no fire.

### What the investigation found

The aircraft sustained substantial damage from the release of high-energy engine debris. The No. 3 engine's low pressure turbine casing, stage 1 low pressure turbine rotor, and exhaust cone separated from the engine. The rotor fragmented, and pieces were found lodged in the right wing leading edge slat area, the left wing trailing edge flap area, and up to 2,500 feet south of the runway.

The debris caused an uncommanded retraction of the right wing outboard leading edge slat. It also severed hydraulic lines, resulting in the loss of fluid for the Nos. 1 and 3 hydraulic systems, and damaged components of the electrical system, the No. 3 engine control system, and the fire protection system. The firewall fuel shutoff capability was lost, and the fire extinguishing agent discharge line was separated.

Teardown of the General Electric CF6-50C2 engine revealed that the stage 1 low pressure turbine rotor had separated from the stage 2 rotor. The two rotors are normally attached by 60 bolts. Examination showed that some of these bolts had failed, freeing the stage 1 rotor from its torque load, which allowed it to overspeed and burst.

Inside the low pressure turbine module, investigators found five severely oxidized and battered fragments of M-50 alloy steel. The stage 1 to stage 2 bolt heads were also smeared with M-50 alloy steel. The engine's main bearings are made of M-50 alloy steel, but all main bearings forward of the low pressure turbine section were undamaged. Because the cavity where the fragments were found is sealed from the path of gas flow, the material could not have migrated there while the engine was in operation.

The evidence appears conclusive that the fragments were either inside the module when it was installed or got inside during the last disassembly and were not detected. The battered condition of the fragments precluded matching them to specific tools, and the Board could not identify their source. The impingement of this foreign material damaged a sufficient number of the 60 bolts to destroy their capability to hold the rotors together.

The investigation also analyzed the uncommanded slat retraction, which occurred because rotor fragments cut the slat follow-up cable and hydraulic fluid was lost. Although the slat retracted, the Board noted that V2 speed was 6 KIAS faster than the slats-retracted stall speed. The Board concluded that had the engine failure occurred at or after V1 speed, the flightcrew should have been able to continue the takeoff safely.

### Probable cause

The National Transportation Safety Board determined that the probable cause of this accident was "the failure of quality control inspections to detect the presence of foreign material in the low pressure turbine cavity during the reassembly of the low pressure turbine module after installation of the stage 1 low pressure turbine rotor disk. The foreign material in the low pressure turbine cavity damaged the bolts holding the stage 1 low pressure turbine rotor disk and stage 2 low pressure turbine rotor disk together. The bolts failed at high engine thrust and the stage 1 low pressure turbine disk separated from the low pressure turbine rotor assembly, oversped, and burst."