'We're having so much fun!"

Not what you expect to hear from the composer of a new evening-length ballet for which neither the music nor the choreography was complete only two weeks before its world premiere. But, despite long days of hard work and little sleep, New Zealand's Rosie Langabeer seemed utterly sincere, remarkably relaxed, and infectiously enthusiastic when she said this at a late-June open rehearsal of BalletX's Sunset, o639 Hours, opening Wednesday.

Inside the Performance Garage on Brandywine Street, while Langabeer rehearsed the musicians, choreographer Matthew Neenan worked with the company's dancers: 10 first-rate artists in shorts, tank tops, and pointe shoes. As though he had all the time in the world, Neenan calmly taught them new steps, adjusted and refined old ones.

Mind you, he had good reason to be confident. The 40-year-old resident choreographer for Pennsylvania Ballet and co-artistic director of BalletX routinely sees his own works performed alongside those of Christopher Wheeldon, Twyla Tharp, and George Balanchine. Neenan is a prolific and popular guest choreographer whom New York Times critic Alastair Macaulay has called "one of the most appealing and singular choreographic voices in ballet today."

Langabeer, 34, is no slouch, either: An award-winning creator of music for circus, dance, film, and theater, she plays an enormous range of instruments and thrives in multi-disciplinary, improvisational situations. In short, these people know what they're doing.

Yet, even after observing this rehearsal and interviewing both Neenan and Langabeer, it is difficult to imagine the ballet as a whole, because Sunset, o639 Hours is nothing if not ambitious. It was inspired by the true story of Capt. Edwin Musick, a pioneering Missouri-born aviator whose exploits for Pan American Airways led to his handsome face's appearing on the Dec. 2, 1935, cover of Time magazine, the most famous pilot in the world.

Among his many accomplishments, Musick inaugurated Pan Am's mail-delivery route between San Francisco and Auckland, New Zealand, via Hawaii and Samoa. On Jan. 11, 1938, his Samoan Clipper exploded in midair after taking off from Pago Pago, killing him and his six-member crew.

A plane crash doesn't immediately suggest ballet, and airmail seems awfully old-fashioned in today's digital world. But this story intrigued Langabeer, who has unruly dark hair, a warm smile, and a sense of endless possibilities.

Raised in Auckland, Langabeer didn't learn about Musick in her home country - despite the fact that for many years her mother attended a string-quartet workshop at Musick Point, a nature reserve named after the pilot. Instead, she first came across his story while doing Internet research in Philadelphia, where she had come in 2010 to perform with the Pig Iron Theatre Company in that year's Live Arts/Fringe Festival, through which she met Neenan.

She suggested he use the Musick material for BalletX in the 2013 Philadelphia International Festival of the Arts, whose theme was time travel, but the research and logistics proved too complex for that. Hence, the two-act, 15-scene work that premieres Wednesday at the Wilma Theater.

Zachary Kapeluck plays Musick; other dancers appear as his flight crew, Pacific Islanders, tropical birds, and - in a remarkable transformation - the plane itself, from engine to wings. Their movement complements Langabeer's rich, multilayered soundscape: a combination of traditional Samoan chants, 1930s-era cabaret songs, and many other kinds of music, plus a host of airplane sounds.

The score is played on conventional instruments (piano, guitar, ukulele) and on sound-producing sculptures with wonderfully odd names like magnapooter, thumbsnake, and anaplumb. There is also singing, by the gifted Andrew Marsh. And Sunset, o639 Hours makes skillful use of "fantasy letters" composed and read aloud by the performers; these represent the mail that was destroyed in the crash. Like every other aspect of this ballet, the letters are based on extensive research. They are also remarkably moving.

This new work fulfills the mission of BalletX: to promote the creation of original, experimental choreography that does not sacrifice the rigor of traditional ballet technique. But it does more than that, touching on such issues as courage, the evils of colonialism, and cross-cultural artistic influence.

It is also educational. As Langabeer pointed out, "Americans don't know much about the South Pacific islands." "There are more Samoans living in New Zealand than in Samoa," she noted. So it was important for her to create a piece honoring the indigenous cultures Musick visited on the several legs of his final flight.

Neenan described the three weeks he spent doing research in New Zealand last summer as "life-changing." But it was obviously impossible to bring Pacific Island performers here, or to spend the time needed to learn, and teach, traditional dances from these cultures. Instead, Neenan said, "We've created our own movement vocabulary for this piece," inspired by what he heard and saw on the other side of the world.

(By the way, that title - Sunset, o639 Hours - was the publicity-shy Musick's terse response when Pan Am's publicity director asked him to describe what he was seeing, during another flight over the Pacific.)


Sunset, o639 Hours

Wednesday to Saturday at the Wilma Theater, 265 S. Broad St. Tickets: $22-$40. 215-546-7824 or modonnell@balletx.org