Safety interlock mechanism for aircraft ground power units

A safety interlock mechanism for use on a ground power unit of the type providing electrical power to an aircraft by means of an electrical cable having an electrical plug at one end thereof, the power unit being carried by a trailer having a tow bar for attachment to a motor vehicle for moving the trailer for one location to another, said mechanism comprising

• a tow bar catch mounted on said towing arm,
• a box mounted on the trailer, said box having an opening positioned to receive said tow bar catch and a receptacle for receiving said electrical plug,
• a hinged plate mounted in said box and having tabs at one end for engaging and preventing said electrical plug from being removed from said box when said tow bar catch is not fully in said box, and a locking pin for engaging said tow bar catch when said electrical plug is not fully in said receptacle,
• means for biasing said hinged plate to move said locking pin into position to prevent removal of said tow bar catch when said electrical plug is not fully in said receptacle,
• a trip arm for moving said locking pin out of engagement with said tow bar catch upon insertion of said electrical plug fully into said receptacle, and
• a latch mechanism for preventing said hinged plate from moving clear of said electrical plug when said tow bar catch is not fully in said box, whereby either the electrical cable or the tow bar catch may be removed from said box, but not both at the same time.