Gulfstream Aerospace G-IV N926TT incident near Sioux City, Iowa

Probable cause

A No. 2 (right) engine failure due to a spinner fairing separation and subsequent impact with the fan blades that resulted in a midspan fracture of one fan blade. The spinner fairing separated as a result of a fatigue crack that originated from the heat affected zone of a tack weld that secured a spacer to the aft side of the fairing. Contributing to the incident was inadequate spinner fairing inspection procedures that did not require removal of the spinner fairing to inspect the aft side for earlier detection of crack indications.

NTSB analysis

The No. 2 (right) engine failure was caused by a spinner fairing separation due to fatigue cracks that originated from the heat affected zone of a tack weld that secured a spacer to the aft side of the fairing. The separated fairing impacted the leading edge of the fan blades and the inner barrel of the fan case and inlet cowl and fractured one fan blade (position 7) at the midspan. The subsequent fan imbalance resulted in severe vibrations that caused an anti-ice air line b-nut connector to back off, the P3 limiter to separate from the fuel flow regulator (FFR) at the mating flange, and a fuel line fracture at the acceleration reset solenoid. The fuel line fracture at the acceleration reset solenoid resulted in a fuel leak that persisted until the airplane landed. There was no evidence of undercowl fire or thermal damage on the engine or nacelle.

The flight crew reported temporary difficulty moving the No. 2 engine fuel shutoff cock (SOC) to the closed position and advancing the No. 1 (left) engine throttle from the idle position following the engine failure. The No. 2 engine fuel SOC and No. 1 engine throttle were cycled multiple times, and the associated linkages to the engine were inspected with no indications of binding, deformation, or other anomalies. Rolls-Royce and Gulfstream reviewed their system designs and did not identify an interlock or other mechanism that would have prevented normal operation during the incident flight.

The operator was in compliance with the regular spinner fairing inspection interval in accordance with the aircraft maintenance manual (AMM) and the last inspection was performed in October 2022, 542.2 hours before the incident flight. The AMM procedures at the time of the inspection did not include a step to remove the spinner fairing from the nose cone to perform a 360 degree visual inspection. The origin of all Rolls-Royce Tay model spinner fairing crack findings to date has been the heat affected zone of the tack welds that secure spacers to the aft side of the fairing, and therefore, early crack detection would have only been possible if the spinner fairing was removed to inspect the aft side. It is unknown if the crack on the incident spinner fairing had grown to where it was visible on the forward side of the fairing during the October 2022 inspection. The inspection procedures were revised in October 2023 to incorporate removal of the spinner fairing in response to this incident.

Text from the NTSB. Open the NTSB docket for ENG23LA030 for the full record.