The Gulfstream G500 is entering the final stage of its flight-test and certification program, while its larger G600 sibling recently completed field performance testing, the Savannah, Georgia-based aircraft manufacturer announced on Monday. “Both programs remain on track and are methodically moving toward their respective type certifications,” said Gulfstream Aerospace president Mark Burns.

To date, five flight-test G500s have accumulated more than 4,250 flight hours over some 1,175 flights. The fourth flight-test G500, dubbed T4, is set to begin function and reliability (F&R) testing, which marks the capstone of the flight-test program. Over the FAA-mandated 300 flight hours of F&R testing, T4 will be used to evaluate how the aircraft behaves in conditions representative of normal in-flight operations, including hot, cold, and humid environments.

“Gulfstream has gone beyond what the FAA requires for certification by flying a fully outfitted production G500 more than 400 hours,” the company said. This aircraft is currently on a world demonstration tour and being displayed this week at the Singapore Airshow.

Meanwhile, the G600 has amassed more than 1,395 flight hours over about 360 flights. Next on the aircraft’s schedule is FAA certification testing for flyover noise.

G500 certification is expected by the end of the first quarter, with G600 service entry to follow later this year.