Could a quite spectacular speculative bubble pop in the next few years? Most of the world's airlines are ordering a lot of commercial transports, perhaps more than they need. If this is the case, cancellations may not be far behind, to be followed by a serious industrial crisis. In light of overcapacity, manufacturers would have to slash production rates. Such a worst-case scenario is said to be a hot topic behind closed doors in Toulouse and Chicago because both major manufacturers are selling significantly more aircraft than they currently produce.

Their backlog is impressive, to say the least—more than 5,000 aircraft each—while last year they delivered a combined 1,274 “next-generation” single-aisles and widebodies. Most industrial segments can only dream about enjoying such a bounty.

But is everything as rosy as financial analysts claim? This key question must remain shrouded because both Airbus and Boeing zealously guard details into the inner workings of their backlogs. This much in known. Last year, an estimated 650 aircraft were definitively parked.

Although the ongoing financial upturn has led to slightly increased production rates—mostly for the A320 and 737 series—the two rivals do not plan to expand beyond that. They certainly fear the damage a global downturn could inflict to their industry. And they also believe some customers, including startups and low-fare players, are excessively optimistic when devising long-term fleet planning and could face serious difficulties when it comes to paying for their orders. Manufacturers are experts in overbooking and most probably sell some aircraft to more than a single customer to avoid the risk of having to park white tails in front of their final assembly lines, where they'll gather dust for who knows how long.

The key question, today, is to try to determine if the airline industry will continue to be dominated by economic cycles—as it has been in the past several decades—or will instead enjoy a long-lasting stability. The International Air Transport Association's recent robust financial forecasts indicate its 240-member airlines will post nearly $20 billion in combined annual profits after achieving disappointing results over the past several years. However, again, this does not mean airlines are insulated from financial losses farther down the path, which could force them to cut capacity and cancel aircraft orders.

Contrary to the projections of other experts, Paris-based ID Aero—a noted consultancy covering the airline industry, including in-depth traffic analyses—does not see a downturn materializing later in the decade. Chief Executive Jacques Delys is adamant that if a downturn were to occur in the next three years it would be of limited scale. Since the 1970s, he says, airlines routinely entered into a series of downturns—of limited duration—about every 8.5 years. During those periods some aircraft deliveries had to be delayed and rescheduled, usually by two years.

Based on past experience, Delys adds, the next downturn could in theory begin in late 2015 or early 2016, and some aircraft deliveries could be put on hold starting in 2017. But this is not the most probable scenario, he says. After all, in the next 20 years, airlines will need to take delivery of an estimated 23,000 aircraft, either to replace the aircraft that age out of their fleets or to create additional capacity. Traffic growth is expected to average about 5% per year—less than 2% in mature markets such as the U.S. and significantly more in the Pacific Rim and other burgeoning regions. This year, traffic growth is spiking above predictions, at 6.6%, while seat-load factor in the last few weeks increased 0.8% to 78.5%, according to ID Aero's calculations.

Delys, like other dependable economists and analysts, acknowledges that there is no concrete information available regarding Airbus's and Boeing's backlog management plans. However, cancellations, including regional twinjets, last year covered 346 aircraft at the most. Cancellations peaked at 467 in 2011, at the end of a serious crisis.

To maintain flexibility, airlines also could begin to favor medium-size twin-jets, which are easier to adapt to various types of routes. This use of twin-jets explains why average capacity is increasing more slowly than previously expected—to no more than 170-180 seats—a market segment that may encourage Boeing to develop a successor to the 757. Airbus has no such plans afoot.

In other words, the situation is and will remain fluid.