The other day, I was viewing the GA activity at Pontiac Oakland International Airport in Michigan, USA.  A very interesting Jet taxied up, it was a Falcon or Rockwell twin engine BizJet. 

The strange thing was that attached to the Verticle Fin was a cable or line, about 75 feet or 25 meters in length with a small pod or device at the end. The jet took off with this trailing behind.

About 30 minutes later, the jet landed with the line and pod trailing behind. As soon as the jet turned off the active runway, several men in a van came up and picked up the pod and line and placed the pod in the van, then followed the jet to where it parked.

What Was It?

Thanks for your thoughts.