The local T-18 guru used to perform first flights for new T-18s, with the builder along to monitor the gauges/engines/radios etc. Worked very well. Lost the engine on one such flight. He shoved the nose down and established a glide back to the nearby airport. "Hey, we've lost the engine!" he told his builder/co-pilot.
The builder tapped the tach..."No, we didn't," he said, pointing at a the tach, showing the RPM of the *windmilling* engine.
All landed OK.
I like the concept of the program, but it's fraught with danger. I'd like to see specific qualifications required of the second person (e.g., X hours in the same make/model, involvement in ground testing, etc.) and have them listed in the Phase 1 Flight Limitations by name.
Ron Wanttaja