Where can I find more about a cargo pickup technique that doesn't require landing the plane? A number of years ago, I read about a technique for cargo pickup and recovery at remote sites using a low-and-slow-flying plane.  The plane would enter a slow orbit around a point on the ground and lower a bag to the ground on a long (hundreds of feet?  A thousand feet?) line.  Once the bag was down, the plane would maintain its turn around a point so that the line stayed slack and the bag stayed in position.  Cargo (perhaps mail?) could be retrieved from or placed in the bag, then once the transfer was complete, the plane exits the circle and lifts the bag.  I'm a lot less clear on that part.

However, I don't have any idea where I read about this, and haven't been able to find any more descriptions of this.  Can anyone tell me if this technique is real, what it's called, where/when it's been used?
See the notes on this page under the "Delivery" section. Looks like its formally called " long-line loiter". There is a brief note on it here and a US Patent here and this manual from the 70's that seems to show how to do it and some related research on it. 

Here is a nice image of the maneuver