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Abstract
The Fuel Quantity Indication System (FQIS) in aviation, particularly in the Boeing 777, relies on ultrasonic sensors for accurate fuel level measurement. However, these sensors exhibit several critical issues, including inaccurate readings, failures due to fuel ingress, and high maintenance costs. This research investigated the root causes of these issues and compared ultrasonic sensor performance with capacitance sensors employed in the Boeing 787. Utilizing a combination of direct observation, engineer interviews, and literature review, the study employed Fishbone and 5W analyses to identify the root causes. Key findings revealed that ultrasonic sensor failures stem primarily from adhesive failure in potting seals, leading to fuel ingress and inaccurate readings. Design, material, and environmental factors also significantly impact sensor reliability. Comparative analysis demonstrated a lower reliability rate for ultrasonic sensors (78.61%) compared to capacitance sensors, which maintained 100% reliability over the same aircraft lifespan.