Can anyone tell me what happens when these sets "lose air" as i was on one this morning that undershot the platform by 1 carriage, and guard just said he "lost air"
Sounds like the driver may have lost his/her air after tripping an intermediate trip at a station. Losing the air means once the trip is activated, the train dumps its air in order to bring the train to a stop as quick as possible.
This can happen at places like Central and Hornsby that require low speed in order for the train stop arm to lower.
I may be wrong but that's my take on it.