Five decades after jets wiped out large Western propeller airliners, the turboprop is pushing back. Until the arrival of the much-heralded propfan, it will not recover the trunkline ground it occupied until the 1960s, but pressure is building to expand the turboprop in the role that it has held since then as a fuel-efficient, short-haul passenger aircraft.

By the 1970s, the largest Western turboprop airliners surviving in production carried only about 50 passengers at modest speeds and over short ranges. A move back up to 70 seats in the 1980s and 1990s was confronted by renewed jet development in that size range and even in the 50-seat category. Around the turn of the century, when aviation kerosene dipped to $37 a barrel, the turboprop airliner looked just about dead.

What a difference an eightfold rise in fuel prices makes. ATR is now straining to meet demand for the 70-seat ATR 72, which, more than its high-performance competitor, the Bombardier Q400, is optimized for fuel economy. And, amid a general upward drift in airliner sizes, ATR's engineering team is one of five that are looking closely at building turboprops with at least 90 seats. The Franco-Italian company reckons the world will buy 1,340 such aircraft over the coming 20 years and says all its major customers want 90-seaters.

Despite the general similarity in appearance of turboprop airliners, at least four of the designs have crucial differences in cross-section, power and multi-version seating. Whichever of the five proposed types go to market—and it is unlikely that all will—they should be well-differentiated products, supporting the manufacturers' pricing power.

The proposals also vary in timing and probability of launch. Ranked roughly by those criteria, the five projects are the Avic MA700; the Regional Transport Aircraft (RTA) of India's Hindustan Aeronautics Ltd. and the National Aerospace Laboratories; an aircraft from ATR; a possible stretch of the Bombardier Q400; and, least defined, the Korea Aerospace Industries DRA, backed by parts of the South Korean government.

Avic Aircraft's MA700 is due to go into service in 2018, but so far only with 78 seats. A longer version, the exact size of which is not yet fixed, will probably follow in the early-to-mid-2020s, if development is smooth. China's record in developing commercial aircraft is not reassuring. The ARJ21 regional jet by Avic spin-off Comac is seven years behind schedule, and the timetable for the successor C919 is close to missing its delivery target. But, having built the Antonov An-24 under license and then updated it twice as the MA60 and MA600, the Avic engineers have learned to crawl and walk before trying to run.

India's RTA is due for program launch in September, but it also would compete with current aircraft at first, beginning with a 70-seat version planned to enter service in 2020. The first stretch version is set to have 90 seats and, again, would probably not appear until well into the 2020s, even if the 70-seater is delivered on time. Seven years is a generous schedule, but the Indian team has less experience than the Chinese in commercial aircraft and Indian aircraft programs tend to be late. The development budget is 43.55 billion rupees ($726 million).

ATR thinks it can develop its proposed aircraft in five years for $2 billion but does not expect shareholder approval this year. One of its two owners, Finmeccanica, is keen to proceed, but the other, EADS, is withholding permission, reluctant to send engineers from its busy Airbus subsidiary to help develop the aircraft. Airbus believes in the concept, however, and Finmeccanica subsidiary Alenia Aermacchi has said it will build a 90-seat turboprop without EADS, if necessary. So the prospects for a launch, whether Franco-Italian or just Italian, look very good, although the timing is less certain.

While waiting to launch a design that is ready to go, ATR is still working on refinements, because an aircraft's costs are determined early in its development, stresses Chief Executive Filippo Bagnato. Once the preliminary design is adopted, the opportunities for improvement are much more limited.

Meanwhile, Bombardier is studying a stretch version of the Q400. “We do believe the Q400 NextGen aircraft is an excellent baseline platform for a future 90-seat turboprop aircraft, as it already has the best seat-mile economics in the turboprop segment,” says a company spokeswoman. “There continues to be a strong interest for a 90-100-seat turboprop and it's an aircraft that customers are asking us about.” The engineering and financial pressures presented by the CSeries suggest that Bombardier will not move early to stretch the Q400, if ever. Notably, however, in this field only the Canadian company can derive its aircraft from a current production type.

The Q400 stretch could also have been the Korea Aerospace Industries (KAI) project, but talks with Bombardier are over or almost over, and the South Koreans, sure they need a partner, are still looking for one, says a non-Korean industry official who has discussed opportunities with them. Details of an indigenous South Korean design, the DRA, have been published by the Korea Institute of Science & Technology Evaluation and Planning. Korean Air would also take part in the program, but KAI, with its larger design office, would surely be the leader.

Ideally, the development of the DRA or an alternative will be predominantly South Korean, so the local authorities can use it to achieve FAA endorsement of their certification capabilities. If South Korea cannot partner with a current manufacturer, then it may conceivably look for a former turboprop builder to consult and another country to share in development. The project's distance from launch undermines its chances, since the market will look less attractive to KAI and any co-investor as competing programs move ahead. On the other hand, the South Korean determination to have experienced foreign help augurs for a dependable schedule.

In terms of design, there are great differences among the proposed concepts. ATR, most radically, wants to build its aircraft with a five-abreast cross section, the widest for a Western turboprop since the 98-seat Lockheed Electra and 139-seat Vickers Vanguard left production in the early 1960s. ATR has made the choice because its 70-seater, the ATR 72, which is based on the 50-seat ATR 42, cannot be stretched much further. The height of the landing gear would limit takeoff rotation too much if the ATR 72 were stretched by more than another seat row or two, so ATR could provide at most 74 or 78 seats with a derivative aircraft.

The large ATR turboprop must therefore be an all-new type and its initial passenger capacity of 90 would be that of its smallest version. Commercial aviation regulations may lead to later versions being quite a lot bigger: Airlines must employ a third cabin attendant when seating exceeds 100. Operating a one-class aircraft with 101 seats is therefore uneconomical. Efficiency returns as the seating rises beyond 101, but a four-abreast fuselage then becomes heavy, because a long and skinny tube needs heavy reinforcement. That explains why ATR is going for five-abreast seating. Moreover, a five-abreast fuselage can be stretched as far as 172 economy seats, DC-9 experience shows.

One might think Airbus would look askance at ATR laying the groundwork for an aircraft seating more than 100 passengers, and potentially a lot more than 100. But the commercial jet builder is studying the regional market and sees new and bigger turboprops as likely, says Kiran Rao, ATR chairman and Airbus executive vice president of strategy and marketing. An Airbus proposal for the concept is called NRA, presumably standing for New (or Next) Regional Aircraft, says an industry official from outside of the program. Alenia Aermacchi also has a concept design.

The design that ATR presented to its shareholders last year and is still refining is likely similar but worked out in greater detail. When it is eventually revealed, such details as the engine, wing area and landing gear height will show how far the joint company expects to stretch its aircraft without major changes. Provisions for growth well beyond 100 seats could add greatly to the production and operating cost of the first version, however, in contrast to the ATR 72's penny-pinching design. The problem appears in the Alenia Aermacchi concept, the 90-seat version of which would weigh a hefty 32.9 metric tons on takeoff, albeit also offering high speed. Penalties will be minimized if the first version of ATR's aircraft has closer to 100 seats.

The exact width of the ATR five-abreast fuselage is unknown, but the company very probably intends to hold weight and drag down by staying close to its current seat-back width of 44 cm (17.3 in.). If the aircraft is optimized for relatively short flights, spacious seating would not be a great selling point. But ATR's choice of a five-abreast cross-section also offers plenty of space for an under-floor freight compartment, which could be attractive to airlines. The inevitably high-mounted wing will not obstruct it.

Drawings published by Avic suggest that its program managers aim to provide a freight compartment in the MA700 by giving its circular cross section a diameter of 3.0 meters (118 in.), unusually large for its four-abreast seating. The compartment may be shallow, but there will also be baggage stowage at the rear of the cabin.

Thanks to the MA700's great diameter, seat backs and the aisle will be 46 cm wide, and the designers have found room for 1.95 meters (6.4 ft.) of standing height in the aisle, compared with 1.91 meters in the ATR 72. Moreover, the floor is positioned for maximum width at the height of the armrests. The result is that, at the expense of fuselage weight and drag, the MA700 should offer considerable comfort for a turboprop. The design does not seem wide enough for optional five-abreast seating.

The South Korean DRA has a circular, four-abreast fuselage and an under-floor cargo compartment, suggests a published drawing. Accordingly, something very close to the MA700 may be planned. But the project seems so fluid that quite a different aircraft could appear.

In India, the RTA's designers have also provided for an under-floor cargo compartment, but have held down frontal area by adopting an egg-shaped cross section, like a traditional double bubble but with smoothly changing radius. They have thereby kept width down to 2.8 meters, not nearly as wide as the MA700's; indeed, the RTA's fuselage width is even narrower than the ATR 72's 2.87 meters, but wider than the Q400's 2.7 meters. The fuselage depth should give the cargo compartment useful height.

Bombardier's stretched Q400, if it goes ahead, will likely have the narrowest cross section and will probably be the only aircraft in the category to rely on baggage stowage at the ends of the cabin, which complicates control of the center of gravity and presents the problem of a high loading position. The narrow fuselage would offer least drag but its weight advantages would be offset by reinforcement needed to support the length. Stretching a circular fuselage of that diameter as far as 100 seats would be quite unusual.

The cross-section choices of the five development teams alone offer considerable scope for marketers to pitch the various aircraft at airlines with the most suitable business model: for example, comfort for the MA700 and freight capacity for the RTA and ATR 90-seater. The ATR aircraft should be fundamentally larger, with at least one version seating more than the others, so it will eventually appeal to carriers that want more seating. But there will be other big differentiators between the competing types: power, speed and climb (see following article).

As to structure, the RTA is planned to have a composite wing, tail and even fuselage. While Indian industry is unlikely to have the expertise to build a fully composite fuselage, such light material as can be worked into the design will offset the weight imposed by the seemingly high aspect ratio of the wing. The ATR 72 has a composite wing, and its manufacturer is probably inclined to use the material for the body of its new aircraft, too. Alenia Aermacchi's concept apparently includes a composite fuselage.

A composite fuselage is controversial not only because of the challenges in production. A turboprop airliner, operating many short flights a day, is far more likely to be banged by ground vehicles than a Boeing 787, for example, and the methods for fixing aluminum structure are well established. Also, the fuel savings from costly light materials are lower for aircraft such as turboprops that spend less time in cruise.

The MA700 will have “at least 15%” composite material, which seems to mean that even its wing will be built of aluminum, while South Korean officials say the DRA would have extensive composite content. In stretching the Q400, Bombardier could make considerable structural changes to that mainly aluminum aircraft, depending on where it sees payoffs.

In addition, however well the products fit the market and the development programs are executed, the newcomers will lack the reputation and established customer base of ATR and Bombardier. Avic is ahead of its Asian competitors, since it has been selling the MA60 and MA600, though not to customers that demand certification recognized by Western authorities. Avic will probably also have the advantage of a protected home market. Not only does the Chinese government impose a hefty import tax on regional aircraft, it can also lean on state airlines to buy Avic's products and on state banks to finance them.

The RTA is similarly aimed at the Indian domestic market, where, unlike China, there is no massive high-speed rail system. KAI's domestic market would be tiny but, again, the South Koreans want foreign help.

Proposed 90-Seat Turboprops
MA700 RTA ATR 90-seater Q400 stretch DRA
Seating, initial 78 70 90 90-100 72
Seating, stretch About 90 90 N.A. 88
Fuselage width, meters (ft.) 3.0 (10)* 2.8 (9.2) 3.4 (11.2)* 2.7 (8.9) 3.0 (10)*
Fuselage height, meters (ft.) 3.0 (10)* 3.3 (10.8) 3.4 (11.2)* 2.7 (8.9) 3.0 (10)*
Under-floor cargo Yes Yes Yes No Yes
Max cruise, kph (kt.) 650 (351) 550 (300) 550 (300)* 680 (367)**
Status Launched. EIS 2018 Launch imminent. EIS 2020 Ready for launch but under study pending approval. Under study. Under study. Partner sought.
Sources: Manufacturers