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Every time I deplane a Virgin America A320, I notice that they grab something from the jet bridge, and stuff it between the jump seats. I haven't seen any other commercial airlines with things like this.

item in square

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    $\begingroup$ It may be part of this $\endgroup$ – Dave Oct 6 '15 at 22:44
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    $\begingroup$ It's possibly some part of the bridge control mechanism that, once removed, disables any movement of the bridge. All the time it's on the aeroplane the bridge can't be pulled back, so there's no risk of a gap opening up that passengers might fall through. $\endgroup$ – user11516 Oct 6 '15 at 22:54
  • $\begingroup$ Is the black spiral cable part of the device? If it is, do you know where it is plugged? $\endgroup$ – mins Oct 7 '15 at 7:11
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    $\begingroup$ Looks like someone forgot his umbrella... $\endgroup$ – FreeMan Oct 7 '15 at 15:51
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    $\begingroup$ @mins Loading bridges have key locks on them to prevent unauthorized operation. Agents are supposed to lock them when left unattended. And you're right, the bridge auto-leveler simply uses a sensor wheel at the door. $\endgroup$ – newmanth Oct 12 '15 at 5:08
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It is a temperature probe for the preconditioned air (PC air) unit.

Bleed air is required in order to operate the air conditioning packs on an aircraft*. Thus, either an engine or the auxiliary power unit (APU) must remain running, burning jet fuel. PC air pumps heated or cooled air into the aircraft and allows the pilot to shut down the engines and APU to conserve fuel.

This is what the system looks like from the outside:

enter image description here

A probe (located in the passenger loading bridge) is inserted into the cabin to regulate the air temperature while PC air is hooked up and running.

Upon parking, ground crews will typically hook up both ground electrical power and PC air, especially if the aircraft will be parked for any length of time. Since the air hose takes some time to unroll and roll, PC air may not be used if the flight is a "quick turn" and the APU will be left running.

* Except for the Boeing 787, which has a no-bleed system.

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    $\begingroup$ Of course! An image of the cabin probe on the bridge (source). $\endgroup$ – mins Oct 12 '15 at 7:08
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    $\begingroup$ Nice! Thank you, I learned something new today. $\endgroup$ – DeltaLima Oct 12 '15 at 17:52

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