(Adds more orders, details, background)
* Qatar Airways finalises $19 bln order for 50 Boeing 777X
* Airbus ahead in air show race, but Boeing closes gap
* Airbus shares fall on projected dip in A330 production
* Airbus seeks to reassure on A380 door upgrade
FARNBOROUGH, England, July 16 Airbus and Boeing climbed close to the $100 billion mark for plane deals at the Farnborough Airshow on Wednesday, demonstrating demand for new passenger jets despite concerns raised by their already record full order books.
Recent profits warnings from airlines such as Lufthansa and Air France-KLM have stoked fears of a sharp slowdown in demand for new aircraft or even cancellations.
However, shares in Airbus closed down 2.5 percent after the company told analysts it may have to cut output of its best-selling twin-aisle A330 passenger jet to get through a three-year transition towards an upgraded model launched at the show.
Airbus Chief Executive Fabrice Bregier acknowledged on Monday that his company's demand forecast implied that average production over the expected lifespan of the revamped jet project would be lower than the current 10 a month.
Airbus gave further indications to analysts at a meeting on Wednesday that production would slip, participants said.
Reflecting the flurry of activity in the first three days of the show, the biennial event has already outsold the 2012 show, which saw $72 billion of orders and commitments. The tally hit $135 billion at last year's Paris Airshow.
Such deals range for provisional letters of intent to firm orders, and can include the announcement of transactions that may have been listed in order books to unidentified buyers.
Europe's Airbus has racked up over $60 billion in orders and commitments, boosted by demand for its re-engined and more fuel-efficient A330.
However, its U.S. rival fought back on Wednesday.
Gulf carrier Qatar Airways finalised a $19 billion order for 50 Boeing 777-9 X planes and added options to buy a further 50, potentially doubling the size of the deal.
China's Hainan Airlines also announced plans to order 50 Boeing 737 MAX 8 planes worth $5.1 billion at list prices.
Prior to the air show, Boeing had a comfortable lead in orders over Airbus this year, with 649 net orders as of July 8 versus 290 for Airbus.
Late in the day, Airbus sought to reassure participants after a German broadcaster reported the planemaker's plans to upgrade the doors on its A380 superjumbo could mean the programme breaking even later than expected.
A spokesman said Airbus was testing improvements to the doors after incidents mainly involving noise during flights and that it expected the upgrade to be approved in the autumn, and fitted to all planes rolling off the production line from 2015.
He said it was unclear how much the upgrade would cost but that Airbus was "well on track" to reach breakeven on the A380 in 2015, as planned.
Also on Wednesday, Canada's Bombardier reached the 500 mark for deals for its Q400 turboprop model and for its CSeries airliner, as it announced three contracts involving 20 aircraft. (Additional reporting by Sarah Young, Andrea Shalal and Jack Stubbs; Editing by Jason Neely and Mark Potter)