Everyone knows that American engines have advanced design and reliable quality, which are the core points of the sales of American aircraft. During the Cold War between the United States and Russia, Russian-made engines became the biggest shortcomings, especially for civilian engines, in terms of fuel consumption and safety. , the maintainability is very far behind the United States. After the end of the Cold War, Russia introduced a large number of American and European civilian aircraft and used a large number of American advanced engines.
Is the American civilian engine now invulnerable?
This is not necessarily the case. On June 2, 2006, an American Airlines Boeing 767-223 (ER) passenger plane suddenly exploded during a test run at Los Angeles Airport, and the left engine turbine disk disintegrated and flew out. As a result, it penetrated the engine casing and entered the right engine nozzle. Fortunately, no one was injured!
American engines are not 100% reliable.
After the accident, the U.S. Department of Transportation immediately launched an investigation. The accident happened as follows. The cause of the incident was that the pilot reported to the aircraft maintenance staff that when the aircraft climbed from 11,000m to 11,600m, the left engine It was inconsistent with the right side, about 2% smaller, so the maintenance staff conducted a ground test on the aircraft. No one expected that when the engine was pulled back from the maximum operating condition to idle, and the left engine decelerated to 95% N1 speed, a sound was heard. There was an explosion, the left engine caught fire, and the fuselage behind the left and right wings caught fire one after another. Three maintenance personnel immediately shut down the engine, and firefighters rushed to put out the fire!
After inspection, it was found that the left engine turbine was broken into two front and rear sections. The high-pressure turbine stage 2 was thrown out of the engine. A piece of it bounced off the ground, damaging the left and right lower beams of the aircraft's lower fuselage. What's even more bizarre is that this fragment penetrated The fuselage hit the right engine 14 meters away and was inserted into the nozzle. Another large piece of debris crossed a runway and taxiway and flew 760 meters before stopping! Another piece damaged the fuel tanks on the left and right wings, eventually causing the aircraft's fuselage to catch fire.
CF6-80 is a product of of the American GE company. It is installed on many wide-body passenger aircraft. The
CF6-80 engine is a very mature engine. It is installed on many wide-body aircraft, including A300, A310, A330, and . Boeing 747, Boeing 767, MD11 passenger aircraft can be said to be a cutting-edge engine from the 1980s to 1990s. The maximum thrust is in the order of 20-30 tons. The total number of manufactured is more than 3,000 units, and the operating time exceeds 110 million hours. , why this accident happened is very surprising!
After investigation, the part number of the ruptured high-pressure turbine first stage disk is 9362M 58 G07, and the production serial number is MPOT8749. It is made of Inconel 718 nickel alloy; the surface is sprayed with plasma spraying 1 layer T4()0 (cobalt-based alloy) Coating, used for anti-rust and anti-wear. After careful inspection, it was found that the material of the wheel plate was fine. Regardless of composition, grain size, microstructure and hardness, it met the requirements, and the cracking location: the rear end fillet radius of the bottom of the tongue and groove. Comply with high pressure turbine disk design drawings.
The most unacceptable thing is that the fatigue crack starts from a tiny pit at the trailing edge fillet at the bottom of the tongue and groove. This is the culprit, but after analyzing the processing and assembly process of the turbine disk, it has not been found. The reason is that the most fortunate thing about this accident is that although the engine exploded, there were no passengers on the plane, and there was no loss of life on the ground.
Aero engines are very difficult, and any mistake in a small detail may cause serious consequences
Investigators connected several past CF6-80 engine accidents in series and found that on September 22, 2000, and December 28, 2002, the same Boeing 767 aircraft, with the same engine, also experienced engine explosions and spewing out turbine parts during ground testing and during climb-out. However, the aircraft successfully made an emergency landing and no one was injured. At the same time, investigators also found that 5 others An airline reported that the bottom of the tongue groove of the CF6-80 engine turbine disc was cracked. The designed working life is 15,000 cycles, but cracks occurred between 5,000 and 9,000 cycles.
The final result is that the investigators believe that the first stage disc of the engine's high-pressure turbine is caused by a tiny intergranular crack, and the design of the turbine disc is not perfect enough. There is a high stress area at the rear fillet at the bottom of the tongue groove, which makes this The stress at the material is very close to the ultimate strength of the material. As long as there is a little bit of damage, it may cause cracks, and eventually cause the turbine disk to rupture!
CF6-80 is an advanced engine with a running time of more than 100 million hours. The design test time and usage time of GE Company are also long enough, but no one can imagine that such a small rounded corner improperly designed will cause huge consequences. Engine explosion accident!
