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Old 20th Jul 2017, 15:04
  #55 (permalink)  
Concentric
 
Join Date: Jun 2016
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Originally Posted by Mee3
Regardless of what and how much it was retained in the gearbox, chipping criteria is based on calculation and backed by statistical data. Same goes to damage tolerance on the gearbox. Silica related to 2nd stage gear however, is new to many including me. Can you elaborate more?
Obviously there should be no silica inside the gearbox. If it does get in there as contamination during gearbox module or mast installation, or during lubricant filling, its hardness might be a factor in starting the creation of micro-pits by causing surface asperities. Is it an Airbus requirement for lubricant to be pre-filtered and piped into the MGB or is it just poured? Is the air breather protected?

The statistical data is:
G-REDL, one chip detected, misinterpreted, catastrophic failure.
G-REDN, several chips detected, one confirmed as 16NCD13, aircraft allowed to fly, numerous more chips detected, planet gear spalled (669FH).
LN-OJF, zero chips detected, catastrophic failure.
What calculations can you perform on that?

If chips have previously been found to be left in the casing and on the sump plate without being detected, how can Airbus be sure the main lube pump sitting higher off the sump will pick them up and deliver them to this FFMP? The standby pump would be more likely to pick them up but that flow will not pass a detector. That is why I think this modification is more about filtering oil that is then delivered to the planetary spray nozzles than detecting macro particles after spalling.
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