The downwash produced by the CSAR-X (PRV), at mid-mission gross weight, in and around the recovery vehicle during a hover in all operational environments must not impede safe and successful recovery of isolated personnel. These environments include, but not limited to, heavily forested steep mountainous, smooth-level, rough-level, smooth-sloped, and roughsloped terrain in calm and high crosswind conditions. Loose particles such as tree limbs, sand, snow, water or rocks in the hover zone at mid-mission gross weights with SCL in Appendix G must not prevent the Recovery Team or injured and un-injured isolated personnel from conducting safe AIE operations (providing emergency life saving measures to isolated personnel, placement of a non-ambulatory personnel in a hoist recovery device, overland movement, self protection, communication, and swimming). (Emphasis added)

According to POGO Defense Investigator Nick Schwellenbach, however, The Air Force seems to have ignored its own requirement when it picked the Chinook.”

Despite the rotor downwash requirement, the initial competition picked a helicopter—Boeing’s  Chinook—that produces significant downwash, and is prone to accidents due to brownout (swirling sand and dust caused by downwash).  The May 2005 article “Brownout on the Battlefield,” in FlightFax, a magazine by the U.S. Army Combat Readiness Center,

In the past 5 years, there have been 11 Class A, B, and C aviation accidents involving Chinook aircraft with brownouts being the trigger event.  These mishaps have resulted in 16 non-fatal injuries and equipment damage costs in excess of $37 million.

All aircraft will kick up dust, but the Chinook produces the largest dust because of the size of its rotor system and its weight.  (Emphasis added)

A look at data compiled by the U.S. Army shows that the Chinook disproportionately suffers from brownout, and other mishaps and accidents when compared to the overall U.S. helicopter fleet.