Failure of cargo aileron’s actuator
During a ferry flight, in a standard operation condition and at cruising level, a military cargo experienced a double hydraulic system failure due to a structural damage of the dual booster actuator. The booster actuator is the main component in mechanism of aileron’s deflection. The crew was able...
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| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Gruppo Italiano Frattura
2014-10-01
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| Series: | Fracture and Structural Integrity |
| Subjects: | |
| Online Access: | http://www.gruppofrattura.it/pdf/rivista/numero30/numero_30_art_49.pdf |
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| Summary: | During a ferry flight, in a standard operation condition and at cruising level, a military cargo
experienced a double hydraulic system failure due to a structural damage of the dual booster actuator. The
booster actuator is the main component in mechanism of aileron’s deflection. The crew was able to arrange an
emergency landing thanks to the spare oil onboard: load specialists refilled the hydraulic reservoirs. Due to
safety concerns and in order to prevent the possibility of other similar incidents, a technical investigation took
place. The study aimed to carry out the analysis of root causes of the actuator failure. The Booster actuator is
composed mainly by the piston rod and its aluminum external case (AA7049). The assembly has two bronze
caps on both ends. These are fixed in position by means of two retainers. At one end of the actuator case is
placed a trunnion: a cylindrical protrusion used as a pivoting point on the aircraft. The fracture was located at
one end of the case, on the trunnion side, in correspondence to the cap and over the retainer. One of the two
fracture surfaces was found separated to the case and with the cap entangled inside. The fracture surfaces of the
external case indicated fatigue crack growth followed by ductile separation. The failure analysis was performed
by means of optical, metallographic, digital and electronic microscopy. The collected evidences showed a
multiple initiation fracture mechanism. Moreover, 3D scanner reconstruction and numerical simulation
demonstrated that dimensional non conformances and thermal loads caused an abnormal stress concentration.
Stress concentration was located along the case assy outer surface where the fatigue crack originated. The
progressive rupture mechanism grew under cyclical axial load due to the normal operations. Recommendations
were issued in order to improve dimensional controls and assembly procedures during production and overhaul
activities. |
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| ISSN: | 1971-8993 1971-8993 |