What happened
On June 17, 2023, at approximately 1059 CDT, a GULFSTREAM AEROSPACE G-IV, registration N926TT, was performing a flight from Philadelphia International Airport to Charles M. Schulz Sonoma County Airport. While beginning a step climb at FL400, the aircraft's No. 2 (right) engine failed.
The flight crew of the aircraft, operated by Planet 9 Private Air, LLC, secured the failed engine and declared an emergency. The crew diverted to Sioux Gateway Airport (SUX) in Sioux City, Iowa, where they completed a single-engine landing without incident. There were no injuries reported following the event.
The investigation
Investigators examined the No. 2 Rolls-Royce Tay 611-8 engine and found significant damage to the engine nacelle and components. The inlet cowl exhibited multiple impact gouges, including a 12-inch by 7-inch penetration. The right wing also sustained multiple small impacts, one of which penetrated the wing skin.
Examination of the engine revealed that the fan spinner fairing had separated and was missing. The fan blades showed extensive leading edge impact damage, and one specific fan blade was fractured at the midspan. The subsequent engine imbalance caused severe vibrations, which led to several secondary failures:
- An anti-ice servo air line b-nut connector backed off.
- The P3 limiter separated from the fuel flow regulator at the mating flange.
- A pressure fuel line at the acceleration reset solenoid fractured, causing a fuel leak.
Materials analysis performed in Germany identified fatigue cracks on the bolt hole fixture pockets of the spinner fairing. These cracks originated in the heat-affected zone of the tack welds used to secure a spacer to the aft side of the fairting.
Findings
Technical testing determined that the natural frequency of the spinner fairing is close to a specific fan blade vibration mode. This vibration can be excited by pressure fluctuations during high-altitude flight.
At the time of the incident, the operator was following the aircraft maintenance manual (AMM) inspection intervals. The last inspection of the No. 2 engine spinner fairing had been performed on October 12, 2022, approximately 542.2 hours prior to the failure. However, the inspection procedure at that time did not require the removal of the spinner fairing from the nose cone, meaning cracks originating on the aft side would not have been visible during a standard visual check.