This article discusses some specific incidents of uncontained jet engine failures. Such incidents usually involve the failure and disintegration of a rotating disc associated with the fan, compressor, or turbine of the gas turbine. Armed with enormous rotational kinetic energy, the disintegrated parts of a failed disk and its blading can become dangerous flying projectiles. Such was the case of the inflight failure of the Rolls-Royce Trent 900 engine on Qantas Flight QF32 on the morning of November 4, 2010, with 466 passengers and crew onboard. Fortunately, all Flight QF32 passengers and crew were safe and uninjured, after this uncontained engine failure. A similar incident occurred in 1989 with flight DC-10-10, N1819U flight 232 operated by United Airlines. As a result of this incident, the gas turbine industry, airlines, and regulatory agencies have worked diligently over the intervening years to improve disc inspection, crack detection, manufacturing techniques, and fracture mechanics models.
An uncontained engine failure is a jet engine company's worst nightmare. It usually involves the failure and disintegration of a rotating disc associated with the fan, compressor or turbine of the gas turbine. Rotating at many thousands of rpm, a disc holds and constrains metal or composite engine blades, each of which can be subjected to centrifugal forces equivalent to 20,000 gs, or more. Thus armed with enormous rotational kinetic energy, the disintegrated parts of a failed disk and its blading will become dangerous flying projectiles.
Such was the case of the inflight failure of the Rolls-Royce Trent 900 engine on Qantas Flight QF32 on the morning of November 4, 2010, with 466 passengers and crew onboard. The super jumbo four engine Airbus A380 had just taken off from Changi International Airport, Singapore, bound for Sydney.
About 6 minutes after takeoff at 7,500 feet altitude over the Indonesian island of Batam, the Trent 900 intermediate pressure turbine disc on engine No. 2 failed, sending engine parts shrapnel through the engine nacelle and the left wing. Passengers saw several perforations take place on the upper surface of the wing above engine No. 2, resulting in one hole as large as 65 by 80 cm[11,]. Now powered by three of the four engines, the A380 circled to dump fuel (which was also leaking out of two wing tanks, above the failed engine). The Qantas plane then returned to Changi Airport, to land without thrust reversers, using emergency pressurized nitrogen to lower landing gear since the hydraulic system had been compromised by the uncontained engine failure. Controls to engine No. 1 had been damaged, so that the pilots were unable to shut it down after landing. Airport firefighters flooded No. 1 engine with foam to shut it down, further increasing the overall damage cost[22 ].
Fortunately, all Flight QF32 passengers and crew were safe and uninjured, after this uncontained engine failure. As I write this, Rolls-Royce and European regulators have tentatively identified the intermediate pressure turbine disc failure to be caused by an interior oil fire, highlighting an oil leak from oil service tubes for shaft bearing lubrication. Speculation by others include the possibility of a bearing failure, causing the intermediate shaft to break, resulting in sudden overspeed of the turbine disc. More will be known after the Australian Transport Safety Bureau issues a preliminary report.
If engine history holds true, this very serious uncontained engine failure can result in valuable engineering progress, as the reasons for the failure become known. In the introduction of Engineering Progress Through Trouble[33 ], Sir Henry Guy is quoted, who avowed in 1942 that:
“One begins to recognize that falling into trouble, encountering some unexpected difficulty however harassing at the time, is in fact an opportunity for making a fresh advance and most advances in engineering have in fact been made by turning failure into success.”
One historic example of progress through trouble occurred over twenty years ago with the inflight failure of a General Electric CF-6 fan disc and is graphically described in a 1990 U.S. National Transportation Safety Board document:
“On July 19, 1989, at 1516, a DC-10-10, N1819U, operated by United Airlines (UAL) as flight 232, experienced a catastrophic failure of the No. 2 tail-mounted engine during cruise flight. The separation, fragmentation and forceful discharge of stage 1 fan rotor assembly parts from the No. 2 engine led to the loss of the three hydraulic systems that powered the airplane's flight controls. The flightcrew experienced severe difficulties controlling the airplane, which subsequently crashed during an attempted landing at Sioux Gateway Airport, Iowa.There were 285 passengers and 11 crewmembers onboard. One flight attendant and 110 passengers were fatally injured.
The National Transportation Safety Board determines that the probable cause of this accident was the inadequate consideration given to human factors limitations in the inspection and quality control procedures used by United Airlines’ engine overhaul facility which resulted in the failure to detect a fatigue crack originating from a previously undetected metallurgical defect located in a critical area of the stage 1 fan disk that was manufactured by General Electric Aircraft engines.The subsequent catastrophic disintegration of the disk resulted in the liberation of debris in a pattern of distribution and with energy levels that exceeded the level of protection provided by design features of the hydraulic systems that operate the DC-10's flight controls.”
As a result of the tragic 1989 Sioux City accident, the gas turbine industry, airlines and regulatory agencies have worked diligently over the intervening years to improve disc inspection, crack detection, manufacturing techniques and fracture mechanics models. An example of the Sioux City work still ongoing is given in a recent ASME paper by Millwater, Enright and Fitch[55 ].
The troubles we have outlined here, have or will lead to gas turbine progress, which might be best summed by a quote used by Whyte[33 ]:
“Progress is the art of getting out of trouble you wouldn’t have been in if it was not for progress.”