Once again spy photographers have stumbled across the new 5-series-based BMW Progressive Activity Sedan (PAS), also known as V-Series or RFK, in the American desert and showing frameless doors for the first time.

In its early stages of development BMW's PAS was falsely pegged as Munich’s answer to the Mercedes R class, much in the same way the X6 was falsely pegged as a Mercedes CLS competitor. But now, these spy-shots of the PAS clearly show it’s a true fastback, allowing more headroom than in the X6 while being significantly smaller than the Mercedes R-Class. This car-like approach seen on this prototype seems better-suited to BMW’s values than a full-size van, and although these spy-photos do not reveal all of the car’s design, enthusiasts might be a bit disappointed by the car’s rational coupe like design.

The V-Series, PAS, RFK or whatever you want to call it, is expected to debut in September 2009 at IAA in Frankfurt.

In late 2007 BMW CEO Norbert Reithofer revealed plans for several all-new models including a design study called the Progressive Activity Sedan (PAS). Beyond an obscure design brief for the new concept, details have been relatively scarce. It appears the wait will soon be over as a concept version will reportedly be revealed in the next couple of months, with the production model to debut by the end of the year.

No name has been revealed, but everything from PAS, to V5, to 5-Series GT, has been suggested. Whatever it will be called, the new model has been spotted testing in prototype for more than a year now. Spy shots show that the car will pick up many of the lines from the X6, and it's expected to be available in both RWD and AWD configurations.

Also like the X6, the new model will only be a four-seater and feature individual bucket seats with full heating and massage functions. Other design details expected to feature include a hatchback rear with a split-gate rear portal. These new renderings preview the final car's expected appearance.

BMW will once again be stressing the car's coupe-like characteristics just as it did with the X6. Expect to see extremely short overhangs, flared fenders and optional 21in wheels. The wheelbase will stretch just over 3m with an overall length of at least 4.90m, making the new model slightly larger than the X6.

Powertrain options will initially include four different engines as well as the latest EfficientDynamics technology. The new range will kick off with a 245hp 3.0L turbodiesel, followed by a pair of 300hp 3.0L twin-turbo six cylinder engines, one diesel and the other petrol. The range topper will be a 400hp twin-turbo petrol V8.