Incident Overview
On January 6th, 2024, a One Air Boeing 747-400 freighter, registration G-UNET, performing flight HC-311 from Muscat, Oman, to London Heathrow, UK, landed on runway 27L and taxied to the apron without any anomalies reported during flight or landing. During a routine post-flight inspection, it was discovered that a panel was missing from the underside of the left wing. The operator filed a mandatory occurrence report with the UK Civil Aviation Authority (CAA). However, this report was not forwarded to the Air Accidents Investigation Branch (AAIB) for further action.
Two months later, on March 7th, 2024, the missing panel was located in the grass to the left of the touchdown area on runway 27L at Heathrow. The AAIB was subsequently informed and launched an investigation into the incident.
Findings and Analysis
1. Panel Detachment and Location
• The detached panel was found 600 metres beyond the runway threshold, indicating it most likely separated post-touchdown during the deployment of the spoilers.
• The failure occurred due to fatigue cracking in the supporting rib structure of the panel, a known issue highlighted by the manufacturer in Service Letter 747-SL57-101-B.
2. Service Letter Actions
• The Service Letter recommended mitigating actions such as adjusting spoiler support rib clearances to prevent fatigue cracks.
• No documentary evidence was available to confirm these actions were carried out on the incident aircraft. However, subsequent checks on the opposite wing showed clearances within the prescribed limits.
3. Safety Implications
• The aircraft manufacturer assessed that the loss of a wing panel during flight had a low probability of causing injuries or compromising continued safe flight.
• The primary hazard identified was runway foreign object debris (FOD), which posed a risk to subsequent aircraft using the runway. The potential for catastrophic outcomes from FOD is well-documented, as seen in the Concorde accident of July 2000.
4. Mitigation Measures
• Heathrow Airport’s FOD radar detection system, designed to identify debris on runway surfaces, was effective and operational but did not detect the panel as it landed in the grass.
• Many international airports lack FOD detection systems, relying instead on regular visual runway inspections and stringent aircraft design standards to mitigate FOD risks.
Conclusions
The AAIB concluded that:
1. The panel detached due to fatigue cracking of its supporting rib, a known issue documented by the manufacturer.
2. While the aircraft was designed to tolerate such failures without compromising flight safety, the detached panel created a significant FOD hazard.
3. Heathrow’s FOD radar was effective in detecting runway debris but was irrelevant in this case as the panel landed off the runway surface.
Safety Recommendations
1. Fleet Maintenance
• Operators of the Boeing 747-400 should ensure compliance with Service Letter 747-SL57-101-B by regularly inspecting and adjusting spoiler support rib clearances.
2. Enhanced FOD Mitigation
• Encourage installation of FOD radar detection systems at major airports worldwide to improve FOD detection and prevent incidents like this.
3. Reporting Protocol Improvements
• Ensure timely communication of mandatory occurrence reports to relevant investigative authorities like the AAIB to avoid delays in initiating investigations.
4. Runway Inspection Practices
• Airports without FOD radar should review and enhance manual runway inspection procedures to mitigate FOD risks effectively.
Final Note
The detached panel posed no immediate threat to flight safety but highlighted critical vulnerabilities related to FOD hazards. This incident underscores the importance of adhering to manufacturer advisories and improving global airport safety measures to mitigate FOD risks.
Disclaimer
This report is based on information available as of January 8th, 2025. While efforts have been made to ensure accuracy, findings remain subject to ongoing investigations. If you are the rightful owner of referenced materials and wish to raise concerns, contact takedown@cockpitking.com.
