Pubblicato il
final report su questo incidente: se ho capito bene, e qui chiedo aiuto, si è trattato di una perdita d'olio lubrificante avvenuta nella connessione tra il tubo esterno e l'alloggiamento della bronzina che supporta l'albero che collega le turbine di media e alta pressione. Tale olio serve a lubrificare e a raffreddare la bronzina.
La connessione, o forse è meglio dire il giunto in questione, ha subito deflessioni maggiori di quelle previste dal costruttore e in più non erano state previste delle prove per verificare tali deflessioni.
L'aereo oggetto del topic è il VH-OQC, ma si parla anche del VH-OQG, che ha avuto lo stesso problema al motore n° 3.
Da AV Herald:
Cita:
The Australian TSB have released their final report concluding the probable cause of the incident as well as two other incidents, see Incident: Qantas A388 near Ashgabat on Feb 24th 2011, engine oil problem and Incident: Qantas A388 near Delhi on Feb 15th 2011, engine oil problem, was:
The A380 engine oil leaks occurred at the external oil feed pipe connector to the high-pressure/intermediate-pressure turbine bearing support casing because the connection became loose, reducing the clamping force and compromising the seal between those components.
The oil feed pipe connection to the high-pressure/intermediate-pressure turbine bearing support casing was subject to deflection loads that were higher than anticipated by the engine manufacturer and the effects of those loads were not required to be considered during the engine design and testing process.
The aircraft was enroute about 3 hours into the flight when the crew received an advisory indication for a low oil quantity on engine #4. The quantity continued to decrease over the next 30 minutes, the crew descended the aircraft from FL340 to FL280. While levelling at FL280 the crew received an "ENG 4 OIL PRESS LO" indication, shut the engine down and diverted to Dubai.
Maintenance found "oil had leaked from the external oil feed pipe on the No 4 engine where it connected to the HP/IP turbine bearing support casing. Maintenance personnel replaced the oil feed pipe, tested engine operation and returned the aircraft to service. This engine had sustained a similar oil leak on 15 February 2011. The operator reported that since that time, the engine had been operated for 286 cycles and 3,110 flight hours."
The engine manufacturer checked the leaking engine oil feed of VH-OQG which were forwarded for further examination. There was no thread degradation or material distortion, however, the surface of the pipe's ferrule surface had fine radial scoring "gramophone" marks along with surface pitting/bedding marks. These marks did not conform to the manufacturer's engineering specification.
Of the total 16 oil leak events there were 4 between August and October 2011, where the surface of the oil pipe did conform to the manufacturer's engineering specification.
In further analysing the pipe connection the manufacturer found "the anti-rotation features (dogs) could allow the adaptor to move during the tightening of the nut. That could reduce the effective torque on the nut and consequent clamping force on the connection."
The engine manufacturer took safety actions to remove all oil pipes, the surface of which did not conform to engineering specifications, from service. As of current the manufacturer is in the process of "modifying the way that the external HP/IP oil feed pipe was secured to adjacent pipes. In addition, the locking arrangement for the long-reach union nut connector/deflector assembly was being revised and oil tank quantity trends were being monitored for early identification of oil leaks."
Sotto c'è la foto del tubo esterno.
Il meteo su Washington
