Spirit Wing Aviation of Guthrie, Okla., has begun the final phase of flight-testing the Spirit-Lear, a re-engined and modified Learjet 24/25. Extensive testing of all SpiritLear systems was ongoing at press time, with STC approval now expected by the end of this summer–a delay from previous estimates of the first quarter.

The required FAA testing includes hundreds of items, many of which were never performed in the original Learjet 24/25 certification. With the SpiritLear modification, which replaces the Learjet 24/25’s pair of original GE CJ610 turbojets with two Williams FJ44-2C turbofans, virtually all of the aircraft systems are updated to the latest configuration as specified under FAR Part 25. According to Spirit Wing, even those systems not affected by the modification have been upgraded to the latest standard.

As Spirit Wing incorporated these changes, it has seen associated improvements in performance. Some of the notable performance specifications include a max cruise speed of 482 knots; a 430-knot long-range cruise, coupled with a 772-pph fuel burn; and max range of 1,808 nm.

The SpiritLear also incorporates full-time engine inlet de-icing and heating of the wing’s leading edges, which Spirit Wing claims will virtually eliminate the possibility of undetected ice accumulation. It also has a triple-redundant pressurization system, complete with automatic emergency pressurization that can be operated independently from either engine. Additionally, in the event of a major duct failure, air from the separate wing and windshield de-ice system can be diverted into the cabin to provide emergency cabin pressurization.