The National Transportation Safety Board has determined that a fatigue fracture in a critical nose landing gear component led to the emergency landing of Delta flight 1092 in Charlotte, North Carolina, on June 28, 2023.

Accident Description

The flight, operated by a Boeing 717-200, was approaching Charlotte Douglas International Airport when the flight crew lowered the landing gear at approximately 2,000 feet above ground level. The first officer immediately observed that the nose wheel unsafe condition light had illuminated, which was subsequently confirmed through the aircraft’s electronic instrument system.

Following standard procedures, the flight crew initiated a go-around to troubleshoot the issue and complete applicable checklists. After multiple unsuccessful attempts at both normal and manual landing gear extension, the pilots declared an emergency with air traffic control.

The crew conducted a second go-around after air traffic control confirmed the nose wheel was not visible. Having exhausted all options to extend the nose gear, the pilots proceeded with an emergency nose gear up landing. The aircraft touched down approximately 1,400 feet from the runway threshold, and the nose was lowered onto the runway at about 80 knots before coming to a stop.

Following the shutdown and evacuation checklists, and after verification from the fire chief that the area was safe, all 104 passengers and crew evacuated through the forward entry doors using emergency slides. No injuries were reported.

Findings

Post-accident examination revealed that the nose landing gear upper lock link had fractured, preventing the nose landing gear from extending properly. The NTSB’s Materials Laboratory found that the upper lock link failed due to a fatigue fracture.

The NTSB report identified “a fatigue fracture of the upper lock link that initiated along scratch features on the lower surface at the parting line of the forged aluminum component” as the probable cause of the accident.

These scratch features, consistent with tool marks from filing or grinding operations, acted as stress concentration areas for crack initiation.

The investigation revealed that once the fatigue cracks had propagated through approximately one-third of the material cross section, the upper lock link fractured in tensile or upward-bending overstress. Visible crack arrest marks indicated the overstress fracture may have occurred over several load cycles.

The NTSB also noted that Boeing/McDonnell Douglas had issued Service Bulletin 717-32-0002 on Dec. 4, 2001, following a previously reported upper lock link fracture caused by tool marks and rough surface finish. The bulletin provided instructions for inspection and modification of the affected parts.

A significant finding in the agency’s report was that the overhaul facility’s noncompliance with Service Bulletin 717-32-002 contributed to the accident. The upper lock link examined was marked with a “V” following the part dash number, indicating that Service Bulletin procedures had supposedly been performed.

Maintenance records showed that Israel Aerospace Industries (IAI) had performed the service bulletin work in June/July 2009, after the link had accumulated 17,313 flight cycles. A fatigue crack growth analysis estimated 39,059 cycles to failure, which closely matched the 41,257 total flight cycles accumulated on the upper lock link at the time of the accident.

The NTSB concluded that “fatigue cracking likely initiated early in the part’s lifecycle, and the scratches were present in the as manufactured condition, therefore it is likely that the service bulletin was not adequately complied with by IAI.”

Boeing indicated that the upper lock link experiences two major loads (extension/retraction) and several minor loads per flight cycle, with the extension load being higher due to the gravitational force component.

“Assuming major fatigue striations correspond to the extension load, fatigue cracking likely initiated early in the part’s lifecycle,” the NTSB report stated.

The investigation also noted some pitting consistent with environmental attack on the adjacent lower surface near the fracture origin, which may have contributed to increased stress concentrations caused by the scratches.