Embraer has paused the flight test program on its KC-390 medium-lift, multi-mission aircraft after an unplanned upset in early October. The twin-jet was performing tests on its slow flight characteristics with simulated ice formation at 20,000 feet, according to the company. In attempting to recover to cruise flight, Flightradar24 data shows the KC-390 prototype losing 17,000 feet before ADS-B coverage was lost, at one point reporting a vertical speed of -31,000 feet per minute.
Source: avwebScary Stall Halts KC-390 Test Flights