United Airlines to retire its Boeing 747 jumbo jets in 2017

United Airlines plans to fly its last Boeing 747 jumbo jet late this year, retiring its largest planes a year ahead of schedule as the iconic aircraft glides into the sunset.

The decision marks the end of an era for US airlines, which have relied on the humpbacked 747 to bring jet travel to a mass consumer market since the plane debuted in 1970. United flew its first jumbo between California and Hawaii that year.

It's also a reminder of the tough task Boeing faces as it tries to keep its newest 747 model, the -8, aloft amid waning demand for four-engine aircraft. The Chicago-based planemaker has just 28 unfilled orders, after closing 17 sales of the freighter version of the jet last year. Boeing has said it would end production if more orders don't materialise.

"It's a bittersweet milestone -- this jumbo jet with its unmistakable silhouette once represented the state-of-the-art in air travel," United President Scott Kirby said in a letter to employees Wednesday.

The Chicago-based carrier flies 20 of the 747-400 passenger model, which Boeing manufactured from 1988 and 2009. Delta Air Lines, the other US operator, is also parking the jumbo jets this year. Cathay Pacific Airways, ANA, Singapore Airlines and Air France are among carriers that have retired their 747-400 jetliners this decade amid a shift from four-engine aircraft.

See: Cathay's last jumbo jet makes its final flight

See: Singapore Airlines' last jumbo jet makes final visit to Australia

Twin-engine wide-bodies like Boeing's 777 and the Airbus A350 can haul almost as many people over vast distances as aviation's behemoths, the 747 and Airbus A380 superjumbo. United's jumbos burn about 20 per cent more fuel per seat than its newest 777s and require special handling from maintenance technicians. Sourcing spare parts is becoming a headache as more airlines retire their jumbo fleets, according to the airline.