For many years, turboprops were thought of in the past tense: noisy, old-fashioned, uncomfortable, rickety and a world away from the glamour promised by the jet age.
In that dim and distant age of low fuel prices - the 1990s - it seemed as if turboprops would become extinct as Embraer, BAE Systems, Fokker and Saab abandoned the technology and airlines embraced regional jets. But the future is becoming increasingly bright for the two remaining turboprop manufacturers - Bombardier and EADS.
With the -600 series ATR has revamped its product line
The reason for the turboprop resurgence is clear: the rise in fuel prices and the expectation they will remain high. Flightglobal's Ascend Online database shows that in 1998, global jet-fuel prices averaged $0.41 per gallon; 10 years later, they peaked at $3 per gallon. With prices approaching that level once more, turboprops - with their far greater fuel efficiency - start to look a lot more attractive. The move towards tighter environmental regulations, such as the EU's Emissions Trading System, is also driving demand.
"Advanced turboprops will continue to play an integral role in the regional airline marketplace as carriers confront the dual pressures of rising fuel costs and increasingly restrictive environmental regulations," says Bombardier. Of approximately 5,900 aircraft to be delivered in the 20- to 99-seat segment between 2012 and 2031, the company forecasts - based on oil at an average $126 per barrel - that 48% will be modern turboprop airliners, the first time this product category has achieved that degree of market penetration.
"The key advantage of turboprops when compared with regional jets is the low operating and maintenance costs," says Filippo Bagnato, ATR chief executive. "An ATR burns up to 50% less fuel than an equivalent-sized regional jet, and costs much less to buy and to maintain. A fleet of 20 ATR 72s, compared with an equivalent fleet of regional jets, may bring annual fuel savings over $30 million."
Propeller engines have a lower cruising altitude - spending less time on the fuel-thirsty climbing phase - and have slower degradation, explains Rob Morris, senior analyst at Ascend. However, "beyond about 400 knots, turboprops lose their efficiency advantage over jets", he adds.
This means turboprops are used mainly on routes less than 500nm, where time lost by slower flight speed is insignificant compared with fuel savings. In the 50-90 seat regional market, they are building a dominant position. "Only in the last couple of years, turboprops have represented some 90% of the total sales in this category," says Bagnato.
Airframe manufacturers have stopped making 50-seat jets and sales of 70- and 90-seat aircraft are also dropping which, he adds, brings substantial potential for a future 90-seat turboprop. "We estimate a demand in the next two decades for more than 3,100 turboprops within 50 and 90 seats."
Tim Varga, GE Aviation's programme manager for advanced turboprops says he is "getting a lot of interest about working on a 90-seater from airframe manufacturers around the world", although he declines to name them. "I think it will happen. It's just a question of timing." Nor is there any technological barrier to even larger aircraft, although Varga says a 90-seater will have to prove itself commercially before anyone considers a turboprop with more than 100 seats.
More than 100 aircraft have been delivered every year for the past four years, notes Morris. Given that in 2003 only 22 turboprops were delivered, this is quite a renaissance. Engine maker GE Aviation, which is returning to the market with its CPX-38 engine, believes demand could increase dramatically if oil prices continue to rise.
As for the accusation that turboprops are relics of a bygone age, both Bombardier and ATR stress that their aircraft have modern, fully equipped cockpits and cabins. Active noise and vibration suppression technology means flying in a turboprop is not so different to a flight in a regional jet.
"ATR -600s are equipped with the newest Armonia cabin, developed by Italian designer Giugiaro, as well as with a full-glass cockpit avionics suite developed by Thales," says Bagnato. "Regional operators, and passengers, are substantially changing their minds about turboprops." This may be true, but the fact he feels compelled to point it out perhaps suggests there is still some work to do in changing perceptions, particularly in North America.
Nonetheless, Varga says any new generation of aircraft adds to comfort and fuel economy. "The new advanced turboprops will have the same creature comforts as current regional jets in terms of noise and cabin space."
Indeed, the rehabilitation of the turboprop appears so complete, ATR and Bombardier are both considering offering a 90-seater aircraft, while a number of other manufacturers are pondering whether to start building turboprops. There is speculation that Embraer could return to the technology, while Chinese airframers Xian Aircraft and Shaanxi also want to sell 70-seat turboprops by the end of the decade. The Economist has reported that Xian - which has a strong presence in the African market - intends to become the world's number-one turboprop maker by 2020.
"I would not be surprised to see more competition," says Philippe Poutissou, vice-president of marketing at Bombardier's commercial aircraft division. "It's clear there have been other manufacturers interested in turboprops. All we can do is to welcome that competition."
One development that could undermine the turboprop market is the open rotor, which will give turboprop-like fuel economy at jet-engine speeds, if noise problems can be solved. However, turboprop companies seem relaxed. "We do not have open rotor technology on any programme and we are not looking at using it," says Poutissou, while Bagnato says "open rotor technology mainly focuses in reducing fuel consumption while keeping a jet-like speed, but speed is not a key-driving factor in turboprop operations". Open rotor is a complicated technology that creates new issues around noise and vibration, and adds extra cost at a time when jet and turboprop engines are already providing substantial reductions in fuel consumption, he adds.
Turboprops will also become more fuel efficient, says Varga. "The efficiency of the engines is getting better, the propellers are getting better and the process of integrating the two is also being advanced. I see there being incremental improvements in all areas."
Given that turboprops operate in the short-haul market, another possible competitive barrier could be the growth of high-speed rail. Poutissou is unconcerned, despite Bombardier also manufacturing trains: "High-speed rail is a great solution for travel between cities but to make it work, you need a massive investment in infrastructure, so you need very high demand between two points, such as Paris-London. Regional turboprops obviously have a much lower capacity than a high-speed train so they are ideal for smaller markets."
As Bagnato puts it: "The jet mania years are definitely over and due to the substantial advantages in terms of operating costs, fuel efficiency and comfort, airlines and leasing companies are increasingly investing in turboprops."