Boeing 501 Heavy (reg N747EX) lifts off for the first time. (Photo by Jeremy Lindgren)

The largest commercial aircraft ever built in the United States, the Boeing 747-8, took off on its maiden flight Monday afternoon, marking an important step forward for the manufacturer’s iconic—but aging—747 family of airliners. After lifting off from Boeing’s factory at Paine Field in Everett, Wash., Boeing Flight 501 Heavy flew loops around northwestern Washington for a few hours of tests before returning to Everett.

Powered by four of General Electric’s new high-tech GenX engines and fitted with a redesigned wing, the new 747-8 promises to fly further while burning less fuel and carrying more payload than earlier 747 models. (A different version of the GenX is also offered for the new Boeing 787, which completed its own maiden test flight this past December.) In addition to the the Freighter version which flew Monday, Boeing is also building a passenger version dubbed the 747-8 Intercontinental, which is expected to begin flight tests in the next few months.

Able to lift a maximum of 975,000lbs, the 747-8 is the most muscular American-built aircraft ever assembled, out-lifting even the gargantuan Lockheed C-5 Galaxy military transport—only the Russian-built Antonov An-225 Mriya and Europe’s Airbus A380 can carry more. When the passenger version of the 747-8 enters service, it will be the longest airliner in the skies, beating the pencil-esque Airbus A340-600 by about 3 feet.

After its introduction 40 years ago, the Boeing 747 was for decades the state-of-the-art of carrying large payloads of passengers and/or freight long distances. As airlines have sought to update their fleets in recent years, however, the 747 had fallen out of favor among airlines for all but the most specialized of missions, due mainly to the appeal of more efficient large dual-engined jets, including Boeing’s own 777 aircraft. Competition also emerged from Europe’s Airbus consortium, which designed and built its own entrant to the Very Large Aircraft (VLA) market, the double-decker Airbus A380.

The last major update of the 747 took place over 20 years ago, when Boeing introduced the 747-400 series. While the -400 was an outstanding success with over 450 passenger and cargo aircraft sold, orders dried up by the late 2000s, and the last 747-400 rolled off the assembly line in December 2009.

Expected to begin deliveries in late 2010, Boeing has received orders for 108 new 747-8 aircraft. Cargolux, a Luxemborg-based freight hauler, will receive the first 747-8F, while Germany’s national airline, Lufthansa, will fly the first 747-8I airliner.

Boeing 501 Heavy (reg N747EX). (Photo by Jeremy Lindgren)

One of the test pilots waves to the crowd before boarding. (Photo by Jeremy Lindgren)

Smoky startup. (Photo by Jeremy Lindgren)

Taxiing to the active runway. (Photo by Jeremy Lindgren)

T-33 chase plane follows the big Boeing down the runway during its takeoff roll. (Photo by Jeremy Lindgren)

A peek inside Boeing's massive assembly building, where two more 747-8s are under construction. (Photo by Jeremy Lindgren)