We recently found significant cracks in the trailing edge of several stage S-0 stator vanes that showed no signs of impact damage.
To date ATS, LLC has identified stage S-1 stator vane cracks on three flared compressors and recently identified a stage S-1 stator vane that had liberated the top 2in of the vane.
We know of two other 7FA’s that have suffered total compressor failures due to similar stage S-1 stator vane tip liberations. It is very likely the trailing edge cracks would have led to a total vane failure with continued unit operation.
Cracking in this area may be the result of harmonics due to stator vane lock up caused by corrosion. The latest S1 crack was found on a flared compressor with approximately 3,500 fired hours and 579 total starts. We have also identified stage S-0 stator vane cracking in one un-flared 7FA.
Recommendation
Until the Eddy Current inspection can be performed we recommend that users should perform a visual inspection of the S-0 stator vanes using a mirror and flashlight as soon as practical.
Any suspect indications should be dispositioned using Eddy Current. Perform a full eddy current of the S-0 leading and trailing edges plus the top four inches of the S-1 leading edges as soon as possible. Some of the S-0 cracks we have found could only be identified using Eddy Current so this inspection should be performed as soon as possible.
TIL 1509 R3 recommends penetrant testing of the stage S-0 stator vanes. We have determined that inspection process will detect larger cracks but has the potential to miss small, tight cracks.