Off-shore oil drilling and production in regions such as the North Sea and Gulf of Mexico have been a key source of demand for helicopter makers including United Technologies' Sikorsky unit, Finmeccanica's AgustaWestland and Airbus Helicopters. Textron's Bell Helicopter could soon become a bigger player with a new helicopter.
The oil and gas industry now accounts for as much as 40 percent of the roughly $6 billion (4 billion pound) annual sales of helicopters for civil use, making it the biggest non-military segment, according to aerospace research firm Teal Group.
While manufacturers have not indicated that the plunging price of crude has led to cancelled orders or reduced production, some warning signs are emerging.
During United Technologies' annual outlook meeting last month, Sikorsky president Mick Maurer said falling oil prices would "put some short-term pressure on our commercial business." Oil and gas represents two-thirds of Sikorsky's non-military business, Maurer said last March.
The oil slide has already taken its toll on shares of helicopter transport firms, which along with leasing companies are major customers of the manufacturers. With their own fleets, these companies fly crews and material to offshore sites for oil companies. Their helicopters are also used for search-and-rescue missions and other purposes.
Since oil turned south in mid-2014, shares in the big transport firms have followed. CHC Group has dropped 70 percent, Era Group has slumped 29 percent and Bristow Group is down 24 percent. By contrast, the index S&P index has gained about 3 percent over that time.
"It’s a pretty unsettled time in our industry right now," said CHC spokesman T.R. Reid, adding that CHC remained optimistic about long-term demand. "The industry is moving further and further offshore," Reid said.
Bristow, in an emailed statement, said: "While our growth rate may be impacted by the current market environment, Bristow is in good position to weather the downturn in oil prices."
An Era Group spokeswoman declined to comment, citing "quiet period" rules.
While oil transport firms are more likely to be hit initially if exploration projects get cancelled, leasing companies could also suffer.
Leasing companies include Waypoint Leasing, Macquarie Rotorcraft Leasing and Milestone Aviation Group, which in October agreed to be bought by General Electric Co (GE.N) for $1.78 billion. All declined to comment.
Sales of rotorcraft for the oil and gas industry have more than doubled since 2006, outpacing growth in the broader non-military market, according to the Teal Group. Military helicopter sales are worth about $16 billion a year.
To be sure, helicopters are only part of the business for diversified aerospace and industrial manufacturers, and other product lines, including United Tech's aerospace parts unit and Textron's Cessna jet business, stand to benefit from cheaper fuel.
But the oil industry has been by far the biggest growth market for non-military helicopter sales and many new products have been developed for this market, said Richard Aboulafia, an analyst at the Teal Group. "If (oil) prices stay around $50, there could be some real damage to these programs," he said.
Brent crude LCOc1 traded at $48.69 a barrel on Wednesday, near six-year lows, despite a rare 4.5 percent spike.
Between 20 to 30 percent of the demand for off-shore helicopter crew transport is tied to drilling for exploration, while the rest covers traffic to already-producing facilities, said Amy Groeschel, an analyst at IHS Energy.
Exploration and development are more vulnerable to cuts, Groeschel said, because they are tied to projects that could be cancelled.
Helicopters that service oil and gas companies are generally larger and more expensive than those used for search-and-rescue missions or executive travel because they carry large crews and may need to make long trips out to sea.
"What we may see is a pause in new orders being placed," said Chris Seymour, head of market analysis for consulting firm Ascend Flightglobal.
Newly developed helicopters expected to serve the oil industry include Airbus' EC175, and Bell's 525 Relentless, which is due to make its first flight early this year.
Mike Suldo, oil and gas market specialist for Bell Helicopter, said in an email the company was not seeing any slowdown or expecting a marked dent in its business.
"We do not anticipate a significant letup, as many energy companies, operators and national governments are seeking more innovative and modern helicopters."
But analysts are more cautious. "Since a component of sales is to the oil and gas industry, it's unfortunate for the timing of the roll-out," said Brian Foley, an independent aviation consultant.
A United Technologies spokesman declined to comment when asked this week about the impact from low oil prices, citing the "quiet period" close to an earnings release.
Finmeccanica did not immediately respond to a request for comment.
Airbus, which says its helicopters represent about a fourth of the estimated 2,300 rotorcraft used today for oil and gas missions, is not seeing any cancellations as a result of falling oil prices, said Christopher Grainger, vice president for oil and gas sales at Airbus Helicopters.
Grainger said in an email that Airbus expected "things to remain relatively stable" in 2015, but remained in close contact with its customers and the oil companies. "We all have to adapt accordingly."