United Airlines has ordered 100 of Boeing's future 737 MAX 9 aircraft and 50 next-generation Boeing 737-900ERs in a deal worth $14.5 billion.

United Airlines has ordered 100 of Boeing's future 737 MAX 9 aircraft and 50 next-generation Boeing 737-900ERs in a deal worth $14.5 billion.

US giant Boeing clawed back ground in its battle to overtake European rival Airbus as the world's biggest planemaker on Thursday, unveiling a mega aircraft order from United Airlines.

In an announcement made to coincide with the Farnborough airshow near London, US carrier United revealed a firm order for 150 Boeing upgraded 737 single-aisle aircraft worth $US14.7 billion ($A14.5 billion) at list prices.

The order comprised 100 of Boeing's future 737 MAX 9 aircraft and 50 next-generation Boeing 737-900ERs.

Boeing's 737 MAX is an upgraded and more fuel-efficient version of the 737, the world's best-selling commercial airplane, with first delivery due in 2017.

Airbus says its rival A320neo, due to enter service in late 2015, will use 15 percent less fuel than its current best performing A320 model.

"Boeing has not just clawed back ground against the A320neo, but it also puts Airbus on notice that there are going to be more 737 MAX orders as Boeing firms up the commitments it has secured this week," independent aviation analyst Saj Ahmad told AFP.

The United deal brought to more than $US37 billion the value of Boeing's firm orders and commitments it secured for various types of commercial aircraft models over the past seven days, trumping massively Airbus.

"Over the past week, customers have announced orders and commitments for 396 planes, valued at more than $US37 billion," Boeing said on Thursday.

Excluding a deal with Virgin Australia on the eve of the Farnborough event near London and which began on Monday, Boeing secured orders totalling around $US35.5 billion.

Airbus earlier on Thursday said that it had secured a much smaller 115 firm plane orders and commitments valued at $US16.9 billion during the week-long Farnborough event.

"We negotiated to be what we believe to be the best airplanes with the best engines at the best price," explained United Airlines chief executive Jeff Smisek for the reason behind its decision to snub the European manufacturer.

Boeing was playing catch-up after Airbus came out on top at last year's Paris airshow thanks to big orders for its neo series.

Airbus has so far won 1439 firm orders for its neo while Boeing has 649 for the MAX.

Airbus unveiled orders worth a potential $6.35 billion on Thursday in the run-up to the Boeing-United announcement that was made from Chicago.

France-based Airbus said Russian airline UTair had placed a firm order for 20 of its single-aisle A321 passenger jets worth $US2 billion at list prices.

Latin American group Synergy Aerospace meanwhile firmed up a provisional order for nine long-haul Airbus A330 aircraft worth $US1.9 billion.

Irish leasing company Avolon committed to buy 15 A320neos worth $1.45 billion and Lebanese airline MEA proposed to buy 10 of the planes for $US1 billion.

"The market is a little bit slower but (our) target is still the same," said Airbus chief commercial officer John Leahy, who had downplayed the planemaker's chances of big orders at Farnborough ahead of the show.

The biennial Farnborough gathering is a key event in the civilian and military aviation calendar and typically sees Airbus and Boeing battle it out for orders.

This year's event has been a relatively quiet affair compared to other recent major airshows given the backdrop of a weak global economy and government cutbacks to military spending.

"The mood during this year's Farnborough air show was notably more subdued than the mood last year at Paris," analysts at Barclays Capital summed up in a note to clients.

The bulk of Boeing's deals at Farnborough were with leasing companies -- it also secured a $US7.2-billion firm order from Air Lease Corporation and a $US9.2-billion commitment from GE Capital Aviation Services.

Airbus' most prestigious contract was for a firm order of future long-haul A350 planes to Hong Kong airline Cathay Pacific costing $US4.2 billion.

The A350 is a response to Boeing's 787 Dreamliner, which is now flying after long technical delays. But Airbus chief executive Fabrice Bregier conceded at Farnborough that there could be new delays to the delivery of its new long-haul carrier that is due to enter service in mid-2014.

British tycoon Richard Branson meanwhile stole the show on Wednesday, announcing that he and his family would be on Virgin Galactic's first trip into space.

AFP