From 142 logs to one part number.
Grade the library first
The team dropped six weeks of .bin files into the library. Grading ran locally on their own laptops — the payload configuration was under NDA, so nothing could be uploaded to a hosted tool. That constraint was why the logs had never been analysed properly in the first place.
Sorted by grade, the fleet split cleanly. Eight aircraft sat at B or better. Four sat at D or F. Not random — four specific tail numbers, every flight, for six weeks.
Read what the recap already said
Every failing flight carried the same ranked anomaly at the top: Z-axis vibration over threshold, followed by altitude-hold drift a few seconds later. The debrief stated the relationship in one line — the drift was downstream of the vibration, not a separate control problem.
This mattered because the team had spent two weeks tuning the altitude controller. They were correcting a symptom.
Sustained Z-axis vibration precedes every altitude excursion by 4–7 s. The barometer is reading airframe resonance, not altitude. Investigate rotor balance before retuning the altitude controller.
Diff a good aircraft against a bad one
Overlaying TAIL-07 against TAIL-03 — same corridor, same day, same wind — showed the two aircraft tracking together on the ground and diverging the moment the rotors loaded up. TAIL-07 sat three to four times higher on VibeZ for the whole cruise, then fell back in line the instant it descended.
Vibration that scales with rotor loading and disappears at idle points at the rotor rather than the mount. Per-arm current draw was even across all four motors, which ruled out a failing motor or ESC. The four aircraft shared exactly one thing: a propeller batch fitted during the same maintenance window.
Confirm the fix with the same measurement
Props were swapped on all four aircraft and each flew the same corridor. The peak went with the props. Grades moved from F and D to B on the first flight back, and the altitude-hold warnings stopped appearing.
The controller tuning was reverted to fleet standard — those two weeks of changes had been compensating for a mechanical fault, and keeping them would have left four aircraft mistuned.