What happened
On 27 February 2018, a Jetstream 4100, registration G-MAJW, was performing a commercial passenger charter flight when the crew encountered landing gear indication issues during an approach to Sumburgh Airport. Upon selecting the landing gear down, the primary indicator showed the nose landing gear (NLG) was not locked, and the standby indicator failed to show a green light.
After attempting to troubleshoot the issue by recycling the gear and using the emergency extension system, the crew decided to return to Aberdeen Airport. During the return, the crew performed flypasts to visually confirm the gear's position. Although the gear appeared to be extended, the crew assessed that a nose gear collapse during landing was extremely likely. Consequently, they prepared for an emergency evacuation via the overwing exits.
Upon landing at Aberdeen, the aircraft stopped on the runway, and an evacuation was initiated. During the process, the overwing emergency exits sustained damage from ground contact. Despite the intensity of the event, all 18 passengers and 3 crew members evacuated without injury.
The investigation
Investigators examined the aircraft's landing gear systems and the cockpit indicators. The inspection of the primary NLG downlock microswitch revealed that the associated wiring harness had failed due to broken wires within the harness. Additionally, the standby NLG microswitch was found to be out of position, creating a gap between the microswitch plunger and the downlock pin that prevented a proper signal.
The investigation also reviewed the operator's Emergency and Abnormal Checklists (E&AC). It was noted that certain checklists contained duplicated information or inconsistent instructions regarding engine shutdown and fire extinguisher use, which could have increased crew workload under high-pressure scenarios.
Findings
- The primary landing gear indication failed because of damaged and broken wires within the primary NLG downlock microswitch wiring harness.
- The standby indication system failed to function because the microswitch was incorrectly positioned relative to the downlock pin.
- The crew's decision to evacuate via the overwing exits was based on a calculated risk assessment to prevent passenger injury in the event of a gear collapse.
- Discrepancies and duplications were identified within the operator's emergency checklists that could lead to confusion during time-critical operations.
Safety action
Following the incident, the manufacturer initiated revisions to the Aircraft Maintenance Manual (AMM) to clarify the rigging procedure for the NLG downlock microswitch and committed to reviewing all emergency checklist cards for clarity. The operator implemented a fleet-wide inspection of the standby microswitches and introduced a repetitive inspection of the landing gear indication systems every 600 flight hours.