The other day I was spotting at Miami International (MIA/KMIA) and noticed something hanging out of the fuselage.
A man with a green jacket is holding a device attached to a cable. Can somebody determine what that is?
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The ground crew has connected a headset to the communication jack outsiede for flight pushback communication with the flight crew. from b737.org.uk:
The External Power Hatch is located beneath the F/O's DV window. It is used by groundcrew to connect the Ground Power Unit and headset for pushback communications with Flight Interphone.
The service interphone is used by engineers to communicate with the service interphone stations inside the aircraft.
Here is a closeup of the connection point
Image from b737.org.uk
About flight interphone System
The flight interphone system is an independent communication network. Its primary purpose is to provide private communication between flight deck crewmembers without intrusion from the service interphone system. The ground crew may also use the flight interphone through a jack at the external power receptacle.
And here is a nose section of 737-200, showing it from a not so close angle.
Image from rigger.smugmug.com