Image courtesy of Pratt & Whitney

One of the Hartford area’s biggest employers is making a major investment in its East Hartford factory: a 313,000-square-foot office building.

Jet engine maker Pratt & Whitney, a subsidiary of defense giant RTX – formerly known as Raytheon Technologies – plans to tear down an existing, 250,000-square-foot office building at 400 Main St. and replace it with a new, 5-story structure and 1,347 employee parking spaces.

The East Hartford Planning & Zoning Commission unanimously approved Pratt & Whitney’s site plan application Wednesday night.

The idea for a new office building was spelled out in the company’s 2005 master plan for its Rentschler Field campus. The campus dates to the 1920s and whose runways and other aviation facilities are being redeveloped, most recently into a pair of huge warehouses being built by Boston firm National Development.