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Out Of Service (xXK/xXZ)


This mnemonic changes the block in question on the dispatchers display to blue, marking the track as "Out Of Service". For example, this is used in situations where the Dispatchers will give a track and time to a work crew. This is also called a Track Block Stick, or Blocking Device Applied.


The mnemonic for Out Of Service blocks is similar to approach blocks, however, you replace the "A" with an "X". For example, if the block in TrackBuilder is labeled U:WA, the MCP indication mnemonic to light this track as occupied (red) would be WAK. The Out Of Service mnemonic for this block would be WX, making the indication mnemonic WXK, and the control mnemonic WXZ. If in TrackBuilder the block was labeled U:2EA, then the Out Of Service mnemonics would be 2EXK and 2EXZ. Control mnemonics also exist for the Out of Service to be off (In Service, you could say). One convention for these controls would be 2EXZ for "on" and 2EXOZ for "off".

Note that Out of Service information is sent to/from certain field devices and is not used on all railroads.

  • nnXZ bit in a control instructs the plant to apply a lock, e.g. 2EXZ;
  • nnXK bit in an indication confirms block has been applied, e.g. 2EXK;
  • nnX0Z bit in a control instructs plant to release the lock, e.g. 2EXOZ.

There's no separate indication bit for confirming release of a block; any indication without the xxXK bit is adequate for that purpose.

-- Main.BrianSwan - 25 Oct 2006 -- Main.JAlexLang - 21 Mar 2008