Fatigue failure of weld joint of afterburner fuel manifold of a jet engine

A fighter aircraft met with an incident during a routine flight operation wherein pilot noticed a thin trail of smoke coming out from the tail end of the aircraft. Post landing inspection revealed that there was fire in the afterburner section of the aircraft. On investigation, it was discovered that there was a fatigue crack in one of the weld joint of the afterburner fuel manifold which resulted in fuel leakage in the form of streaks. The localized over temperature thus generated was responsible for melting of diffuser casing, adjustable nozzle casing, heat shield and hydraulic pipelines. Through detailed investigation, the sequence of failure in the engine was established. The contributing factors for fatigue cracking of the weld of the fuel manifold were identified and remedial measures suggested for prevention of similar failures.