The Paris air show is performing to plan: Airbus, Boeing and Embraer accumulating airliner orders, and Boeing launching the stretched 787-10 as expected on the second day. But the real story developing at the show is the heated exchange of words between engine manufacturers over whose powerplant is the most technologically advanced.

The aircraft that are making the news at the air show are largely enabled by advances in propulsion technology that allow their manufacturers to offer big reductions in fuel burn over the previous generation – the reductions of 15% or more are what is driving the orders.

Whether it is the Airbus A320NEO with the CFM International Leap-1A or Pratt & Whitney PW1100G, Boeing 737MAX with the Leap-1B, Bombardier CSeries with the PW1500G, Embraer E-Jet E2 with the PW1700/1900G or Mitsubishi MRJ90 with the PW12000G, the engines are critical.

But lower fuel burn comes at a price, and the war of words between CFM (and General Electric) and Pratt & Whitney, in the short term, is more about the impact on maintenance cost of their technology choices. In the long term, it is about their ability to continue to drive down fuel burn.

CFM opened fire at Paris by showcasing the advanced composite blades, ceramic matrix composites, advanced alloys and manufacturing technologies that it says will allow the Leap to beat P&W’s geared turbofan (GTF) on fuel burn and maintenance cost.

Pratt responded by arguing the GTF “is about more than the gears”, and that the core technologies in the PW1000G family are as advanced as makes economic sense in an engine of this class, allowing the GTF to run cooler than the Leap, which should reduce maintenance costs.

It is an argument airlines will continue to make bets on through the air show – and beyond – as they place orders for new aircraft based on manufacturers achieving the fuel-burn and cost savings largely promised by the new engines. As GE and Rolls-Royce have illustrated on the 787, it is hard to meet targets out of the box. And the newly launched 787-10 will benefit from significant improvements that had to be made to the GENx and Trent 1000 to meet the originally specified targets and provide for future growth.

It remains to be seen whether CFM will respond during the show to Pratt’s charge that the Leap’s “exotic” technology will incur a substantial penalty in component prices and repair costs. But the arguing is far from over.

If there are wars of words brewing on the defense side of the show, the protagonists are skirmishing quietly. Italy’s plan to buy Piaggio Avanti-based Hammerhead medium-altitude, long-endurance unmanned aircraft is a significant development. So, potentially, is the grouping of Dassault, EADS and Alenia Aermacchi to pursue a European MALE UAV program – but only if they can get their governments to fund such a thing.

Another sector to keep an eye on is special missions, particularly maritime patrol and surveillance, whether it is Beechcraft’s unveiling of a Baron G58 piston twin with an ISR package or Lockheed Martin’s continued efforts to launch a maritime patrol version of the C-130J. Those at the show, if they can take time to walk around, will see a wide array of special-mission aircraft and system packages on offer.