Sad but true story.....
CH-47C slinging a O1-E Bird Dog airplane. Bird Dog duly rigged with a 4"x4" by 8' piece of lumber on top of each wing as spoilers. Chinook crew being chased by the Recovery crew Huey. Despite radio calls from the Huey crew....the Chinook accelerated to about 110 knots. At that point the Bird Dog despite the wooden spoilers began to fly.....oscillated behind the Chinook....swung forward up in front of the Chinook....and on the second oscillation swung into the rotor blades forward.....Chinook shed all its blades and came apart in the air....fell 2500 feet into the jungle below.
I have recovered three airplanes....an O1-E Bird Dog, a Beaver, and a Cessna A-37.....oddly enough the Army used the sling harness designed for the Bird Dog to lift the Air Force A-37. Half way home with the A-37....one of the four point connection points broke....and the aircraft rolled over on its side with the nose pointing upwards. We got it down on the ground and only damaged one of the tip tanks by bending the wee small wing looking thing on the tip tank.
The Beaver haul was good until one of the wooden spoilers departed....then the ol' Beav got all squirrelly.
Fort Rucker used to have a derelict Lockheed T-33 for a practice sling load.....carried that around quite a bit too.