It sounds like the driver just shut the train down and removed his
keys. The hissing noise would be the air venting to atmosphere when
the train is shut down, therefore locking the brakes on, and when the
keys were removed (or switched off) it cuts off the electrical
circuitry to the outside indicator lights.

The driver is supposed to shut down his train in this manner every time
he has to leave his cab for any reason.



wrote:
I was watiting at South Kensington at about 11pm and an outer rail
cirle line train arrived. A few minutes after it arrived, all the
amber lights on the outside of the train went off and there was a
loud
hissing noise. Some staff wandered up the train and it went back to
normal.

Was this a case of someone pushing the emergency button? Why did
*all*
the amber lights go off while the doors were still open

--
Chris