Bombardier is facing "serious concerns" and is likely to rein in production of its flagship passenger jets in Belfast after it was revealed that the plane maker will deliver just half the number of planned CSeries aircraft this year.
The wings and part of the fuselage are made in Belfast, where the Canadian-owned firm employs around 5,000 staff.
But the company has now said it will deliver only seven aircraft this year, instead of 15, due to delays with engine maker Pratt & Whitney.
Former top Bombardier official Martin J Craigs said: "You can't take it as anything but a concern".
"You radically reduce volume, which means the unit price is more, and it doesn't mean good news for the bottom line."
"But it doesn't mean that their aircraft has become fundamentally bad."
He added the "only logical conclusion" was to rein back production in Belfast.
Bombardier had landed several much-needed orders for its CSeries planes - a programme that has run billions of dollars over-budget.
The manufacturer received $1bn from the Quebec regional government in a recent bailout.
This year, Bombardier signed a deal with Air Canada to sell it up to 75 of its CSeries passenger jets, while US firm Delta also ordered 75.
"(Cutting back production in Belfast) is the only logical conclusion that you could come to," Mr Craigs explained. "What's also troubling is that they are also cutting back production of other jets."
The ex-chief executive of the Pacific Asia Travel Association said that CSeries rivals, such as the Airbus A320 and Boeing 737, were backed up with trying to fulfil orders.
He also claimed Bombardier needed "more innovative marketing to niche users", targeting other airlines and other buyers, aside from big-name airlines.
"(Bombardier needs to) stop depending on getting traffic from established hubs - don't depend on just the usual customers," he said.
"Unfortunately, the components are so expensive, there is no way they are going to build at this rate."
He claimed Bombardier should look at diversifying more in order to quell the impact of an issue like this.
"For reasons out the control of the hard work and expertise in Belfast, it would be a good time to have a good look at more diversification," he said.
Bombardier has said it has adjusted its "CSeries delivery forecast from 15 to seven aircraft as a result of delays by supplier Pratt & Whitney".
Fred Cromer, president of Bombardier commercial aircraft, said: "We are very pleased with the performance of the CSeries during its entry into service with our launch customer SWISS.
"The aircraft is meeting all expectations and clearly demonstrating that it is the best performing and most efficient aircraft in the 100 to 150-seat class.
"The CSeries engine is performing very well in service. We are working very closely with Pratt & Whitney to quickly address this supplier ramp-up issue and to ensure we have a strong supplier base to support long-term growth objectives.
"We are very confident in our production ramp-up plan, including our ability to meet our production goal of 90 to 120 aircraft per year by 2020."
Last month the manufacturer said it was bringing forward 95 planned redundancies.
More than 700 staff are due to go this year, with some 1,080 planned by 2017.
Last month, the Belfast Telegraph revealed Bombardier was moving some of its operations from Northern Ireland to cheaper countries, including Mexico and Morocco.