How NAVAIR isolated a flight-surface vibration fault in days — not weeks

When the crew of a US Navy C-2A Greyhound continued reporting excessive cockpit vibration despite no abnormal readings on the engine's built-in monitoring system, NAVAIR needed a way to instrument the entire aircraft quickly. enDAQ (formerly Slam Stick) vibration data loggers — requiring no wiring — enabled a single engineer to instrument nine locations across the aircraft in 30 minutes, dramatically reducing setup time and enabling rapid fault identification..

Persistent cockpit vibration with no obvious source

Vu Buu, Subject Matter Expert for Vibration Issues at the US Navy's Naval Air Station, North Island, faced a challenging diagnostic problem. The crew of a C-2A Greyhound continued reporting excessive vibration in the cockpit. Despite checking the aircraft's engine vibration monitoring system, no abnormal vibrations were detected—meaning the source was elsewhere and would need to be found through more extensive testing.

Isolating the source required instrumenting accelerometers throughout the entire aircraft over several days. Setting up such a test with traditional wired accelerometers would have been extremely time-consuming and costly—requiring multiple engineers and days of setup time before any useful data could be collected.

• Crew-reported cockpit vibration was not captured by the engine's built-in monitoring system.
• Multi-day, full-aircraft instrumentation was required to narrow down the vibration source.
• Traditional wired accelerometer setup would have required a 3-engineer team and 4 hours per day of setup.
• Some target locations (e.g., the aircraft exterior) were practically inaccessible with wired systems.

Nine enDAQs. One engineer. Thirty minutes.

The US Navy had recently funded development and procurement of Midé Technology's enDAQ (formerly Slam Stick) vibration data loggers. Because enDAQ require no external wiring, power supply, or laptop connection per trial, they were ideal for rapid field deployment across the aircraft.

The NAVAIR engineering team installed 9 enDAQ (formerly Slam Stick) with double-sided tape throughout the aircraft in a broad initial sweep to identify the vibration zone. Installation required just one engineer and took approximately 30 minutes across the three-day test period. A traditional wired accelerometer setup would have required a team of three engineers spending four hours per day—a total of 36 setup hours across the same period.

Once initial data indicated that excessive vibrations were concentrated in the rear of the aircraft, the enDAQ (formerly Slam Stick) were quickly relocated to the aft section for more targeted analysis. Crucially, one installation location was on the outside of the aircraft—a position that would have been nearly impossible to instrument using a traditional wired approach.

Faulty dampener identified, repaired, and aircraft returned to service

Vibration data from the second day of testing pinpointed a faulty dampener on one of the flight control surfaces. This dampener's role is to absorb vibrations from the flight control surface before they transmit to the yoke. The dampener was replaced and final testing confirmed the vibrations had been eliminated—allowing the aircraft to return to service.

Following this success, NAVAIR expanded their use of enDAQ (formerly Slam Stick). The Navy now prefers them for applications where wiring would be impossible, such as instrumenting aircraft landing gear. NAVAIR purchased an additional 280 units after already deploying nearly 200, with plans to acquire 600 units over the following years—projecting $3–5 million in vibration testing savings over four years.