LAS VEGAS (AP) — Pilots with a Nevada glider team have flown to new heights above the Andes Mountains in Argentina using only wind as their engine.

The Las Vegas Review-Journal reports an experimental sailplane built by a Perlan Project team set an unofficial world altitude record for engineless flight on Sunday, then broke that record by more than a half-mile two days later.

Pilots Jim Payne and Miguel Iturmendi flew the Perlan 2 aircraft to 63,776 feet on Tuesday, 3,107 feet higher than Sunday's flight by Payne and Morgan Sandercock.

That's about 3 miles above the highest altitude used by commercial flights.

Payne says "the sky is starting to get dark" at that altitude and the curve of the Earth is visible.