WASHINGTON — Trepidation from parts dealers over a value-sapping glut of used spares has eased in the last year as key metrics, including general economic trends and industry-specific figures like lease rates, have shifted in favorable directions, an ICF SH&E analyst says.

"Last year, we detected more concern about a surplus parts bubble," Richard Brown said Monday at the jointly held Aviation Suppliers Association and Aircraft Fleet Recycling Association annual gathering. "This year, there is more calm."

Brown, emphasizing that his view is shaped by empirical data and not a dedicated survey or project, cited several factors that could account for the change. The largest one is the gradual global economic uptick that is driving passenger demand. International Air Transport Association (IATA) figures show revenue passenger kilometers up 6% in the first four month of 2014 compared to 2013.

The uptick, combined with stable fuel prices, means demand for productive mid-life aircraft—such as Airbus A320s—is rebounding, driving lease rates up. This leads to more follow-up leases on older airframes and pushes part-outs into the future.

Avitas Senior VP Adam Pilarski suggests that values still have room to rise in the current economic rebound. Pilarski says that so-called "base values"—what an aircraft is worth in a stable marketplace in a non-distressed sale—have not fully recovered in the 56 months since the 2008 recession bottomed out.

Despite the general industry rebound, Brown underscored that surplus parts demand, while climbing, remains product-dependent. Boeing 737 Classics offer little of value beyond green engine time, for example, while landing gear are plentiful virtually across the board.

ICF sees the surplus market rising at a 5.5% compound annual growth rate through 2022, climbing from $3.5 billion in 2013 to $6.2 billion in a decade, excluding transactions between dealers. Brown calls this ICF’s "medium growth" scenario, which assumes a slight uptick in interest rates, a slight dip in fuel prices, run-of-the-mill delays in new aircraft programs, and no major disruptive tactics from original equipment manufacturers.

One set of figures that won’t change, Brown says: the general mix of surplus parts types. Engines account for 65% of the market and will continue to drive surplus demand, while components have 35% and will keep it. Airframe parts, always a laggard, will continue to hold a small share.