Crew on an Embraer KC-390 requested an early return to base after the aircraft completing a stall test earlier this month, the Brazilian manufacturer says.

As part of Embraer’s flight certification efforts, a prototype KC-390 transport aircraft conducted a stall speed test on 12 October. But decreased lift force caused an altitude loss that would prematurely call the KC-390 crew back to base, Embraer tells FlightGlobal in a 23 October email.

The crew landed safely at Embraer’s manufacturng and flight test centre at Gavião Peixoto, Brazil, an Embraer spokesman says.

Embraer declines to answer additional questions about the circumstances of the test flight on 12 October or the aircraft's status since then. The flight tracking website has not logged a new flight by the KC-390 prototype, PT-ZNF, since 12 October.

Including aircraft PT-ZNF, Embraer has flown two KC-390 prototypes.

The tactical transport and tanker aircraft are slated to enter service in 2018 with plans to deliver the first two production aircraft to the Brazilian air force that year. The air force plans to take on 28 aircraft total, with two deliveries in 2019 and three deliveries in subsequent years.