LONDON – As UK engine maker Rolls-Royce pushes towards rectifying old issues with the Trent 1000, another issue has arisen. Rubbing wear, which could lead to cracks of the low-pressure turbine discs, has led to a proposed airworthiness directive (AD) from EASA.
It’s a headache Rolls-Royce does not need right now, but one which should not have any significant impact on operators of the Dreamliner.
As a side note, the Dreamliner is a special aircraft because the cabin pressure and humidity level on its 787 are higher than those on other airplanes. Thus, passengers on board feel like they are at an altitude of 6,000 feet, 2,000 feet lower than a standard flight. These changes cut down on passenger fatigue, dry eyes, and headaches.
A New Airworthiness from EASA
EASA plans to mandate inspections of certain Rolls-Royce Trent 1000 low-pressure turbine (LPT) discs following a report from the firm that of the potential for cracks.
EASA’s proposed airworthiness directive (AD), issued July 6, calls for operators of Boeing 787s with Trent 1000 “Package C” variants to inspect LPT stage 3 and 4 disc seal fins for cracks.
EASA said: “Analysis of certain [LPT] discs in service has determined that, due to rubbing contact with interstage static seals, cracks may initiate in the front seal fins which could lead to cracks in the disc of the affected parts.”
Rolls Royce talk about this fact
Rolls Royce said: “We are revising our inspection regime regarding the Trent 1000 Package C low-pressure turbine. Inspections of disc seal fins will be incorporated into the existing in-shop maintenance regime and we do not anticipate it will cause any significant operator engine maintenance burden.”
“We are developing a design solution that will remove the need to inspect these parts.”
Dreamliner Engine Problems
Following assessment of some of the engines in service, mechanics have found that a rubbing contact between the discs and interstage static seals could lead to cracks in the front seal fins.
This could then cause additional damage and could lead to cracks in the disc. In the proposed AD, EASA said, “Analysis of certain LP turbine discs in service has determined that, due to rubbing contact with interstage static seals, cracks may initiate in the front seal fins which could lead to cracks in the disc of the affected parts, as defined in this AD.”
A One-time Inspection
EASA also said, “This condition, if not detected and corrected, could lead to crack propagation, possibly resulting in LP turbine disc failure and high-energy debris release, with consequent damage to, and reduced control of, the airplane.”
In order to rectify this issue, EASA wishes to mandate a one-time, ultra-high sensitivity fluorescent penetrant inspection of the seal fins. If any cracking is evident during the inspection, the parts will need to be replaced.