engine surge problem
Got a problem with a B727 200RE centre engine -17 JT8D. After workshop visit to comply with High pressure compressor disk AD check, the engine surged at high altitude reaching FL350. were able to operate by putting bleed onto this engine.
The workshop then changed the Nozzle guide vanes but we still got the surge at high altitudes and then later on approach at 500 ft.
Another workshop visit and the C1 fan blades were changed, but the air test failed again due to another surge at FL 380 when throttling back to cruise power.
All sense lines, bleed lines and intake duct already checked.
ANYBODY OUT THERE WITH ANY IDEAS ?