• MCP Altitude Locked:

  Indications that the Digital Flight Control System is locked-up are as follows:

  
  

  –Aural warning comes on for 2 seconds then off for 8 seconds and continues this sequence.

  
  

  –Altitude alert flashes.

  
  

  –The altitude that shows on the MCP altitude display is 50,000 feet.

  
  
  50,000 feet Lock-up Possible Causes

  Before replacing any component perform BITE if available. (DFCS/Extended Maintenance/MCP Test/Channel?) or library test 16 for the MCP Interface.

  
  

  1.Mode Control Panel (MCP).

  
  

  2.Flight Control Computer (FCC).

  
  

  3.Air Data Inertial Reference Unit (ADIRU).

  
  

  4.Data bus communication breakdown between MCP and/or FCC’s and/or ADIRU (try resetting the CBs for above LRUs).

  
  

  5.Both FCC’s are powered off.

  
  

  6.DFCS BITE test 62 (AP warning circuitry test) active.

  
  

  7.FCC A and FCC B part number do not match.

  
  
  MCP Altitude Locked:

  

  
  

  

  
  Circuit Breakers:

  AFCS SYS A FCC (DC): P18-1 = D2.

  AFCS SYS B FCC (DC): P6-2 = B3.

  AFCS MCP DC1: P18-1 = D5.

  AFCS MCP DC2: P6-2 = C3.

  ADIRU Left (AC): P18-1 = E7.

  ADIRU Left (DC): P18-1 = E5.

  ADIRU Left EXC: P18-2 = E8.

  ADIRU Right (AC): P6-1 = C14.

  ADIRU Right (DC): P6-1 = C17.

  ADIRU Right EXC: P6-1 = C15.

  
  
  Applicable deferrals None

Training Only