Pre-owned business jet and turboprop inventories eased further in April with more sales transactions thinning the herd, according to the latest data from business aviation market information firm JetNet.

Inventory of used business jets fell to 13.6 percent in April, down by 0.7 percentage points year-over-year. Business jet sales transactions rose 4.1 percent in the first four months of 2012 versus a year ago, while asking prices remained nearly flat, eking out a 0.1 percent gain to an average of $4.22 million. Average number of days on the market for a business jet dropped to 340 days, down 70 from the January to April period last year.

Meanwhile, turboprop inventory fell to 9.2 percent–1.3 percentage points below April last year. JetNet thus considers the turboprop segment a seller’s market, since it has moved below the 10-percent mark. Turboprop sales transactions climbed by 3.1 percent in the first four months of this year, while average asking prices rose by 1.7 percent, to $1.28 million. However, number of days on the market for used turboprops ticked up by 46, to 345.

JetNet said inventory of used turbine helicopters also decreased in April to 6.2 percent, down 0.5 points from a year ago. Asking prices for turbine helicopters fell by 4.9 percent to an average of $1.43 million, however.