Saturday 15th June 2013:

A Gulfstream IV jet carrying former US President George W Bush en-route Philadelphia-Dallas made a precautionary landing at Louisville, Kentucky after pilots reported smelling smoke in the cockpit.

After a short period on the ground, the aircraft continued to Dallas with no further incident.

The Gulfstream IV is a early generation Gulfstream jet, with the series entering service in the early 1980’s (see file pic attached). The type evolved into the current iteration jet known as the G450.

Links:
http://www.philly.com/philly/news/George_W_Bush_flight_out_of_Philadelphia_forced_to_make_emergency_landing.html
http://www.foxnews.com/politics/2013/06/16/plane-carrying-george-w-bush-makes-emergency-landing/