Beyond Cycle Count: Sensor-Based Maintenance Warnings for Simulated Turbofan Engines

Run-to-failure engine data can make a maintenance warning look successful for the wrong reason: elapsed cycle count is already informative about how close an engine is to its recorded failure. This study tests whether measured telemetry adds useful final-window warning information beyond elapsed cycle and current operating conditions. We label a simulated turbofan engine cycle positive when RUL ≤ 20 and use 90 complete trajectories from the public, 100×-downsampled tiny-N-CMAPSS training partition. The corrected input definition uses the 14 measured physical channels documented by N-CMAPSS. It excludes the auxiliary flight-class and health-state fields, unit ID, and RUL. Five outer engine-held-out folds and four inner engine-grouped folds select a threshold for a 5% pre-window false-alert budget. The cycle-plus-operating baseline recalls 55.4% of final-window cycles. Adding the 14 measured channels raises recall to 79.3% at the matched alert budget. The paired engine-cluster bootstrap estimates a 23.9-percentage-point recall gain, with a 95% interval from 18.3 to 29.6 percentage points. The result shows that the measured telemetry in this simulator reduces missed final-window cycles beyond a clock-and-operating-state baseline. It does not set a service interval, validate a fielded aircraft system, or certify safety.