Inventories of business jets, turboprops and turbine helicopters continued to deflate in January, business aviation market information firm JetNet said today in its latest market update.

According to JetNet, pre-owned business jet inventory in January landed at 13.2 percent of the in-service fleet, down 0.5 points from a year ago. Retail business jet sales, however, fell by 1.8 percent year-over-year, “only the second time since January 2009 that it showed a decline in full retail sale transactions,” JetNet said.

The number of business turboprops for sale continued further downward, with this inventory now at 7.9 percent, down 1.4 points from January 2012. Sales transactions increased by 5.7 percent, JetNet said.

Meanwhile, turbine helicopter inventory descended to 6.1 percent in January–0.3 percentage points from a year ago. But turbine helicopter full retail sale transactions fell by 33 percent, from 100 to 67. “This is the lowest number of [turbine helicopter] transactions since January 2007,” JetNet said.