TM 1-1510-218-10 2-52 indicator  shall  display  "0"  on  both  the  digital  and  bar graph display. The  Fuel  Flow  Indicators  are  protected  by  0.5- ampere  circuit  breakers,  placarded   FUEL  FLOW  #1 and #2, located on the overhead circuit breaker panel. 2-40.  ENGINE TREND MONITOR. a.   General   Description.      The   Engine   Trend Monitor  (ETM)  is  a  monitoring  system  that  monitors and  records  data  on  engine  and  airframe  parameters, e.g.,  fuel  used,  cycle  counts,  total  hours,  and  engine and   airframe   exceedences.      It   provides   automatic cycle  and  engine  start  counting  and  automatic  data collection.  The ETM provides maintenance personnel with a complete, accurate, and detailed record of the engine    and    airframe    use.        At    the    time    of    first installation  of  the  ETM  in  the  aircraft,  the  data  in  the ETM   is   revised   with   the   current   pertinent   statistical data  concerning  the  airframe  and  engines.    The  ETM can   also   serve   as   a   log   that   will   contain   detailed records of each event in a flight from power on, engine starts to engine stops, and power off. NOTE When the ETM system is inoperative, pilots are    responsible    for    manually    recording engine trend data. b.  System and Related Components.  (1)   The   ETM   Processor.       The   processor contains the main computer, and is the collection point for data received from the various engine transducers. (2)   The    Airdata    Computer.        The    Airdata computer   provides   airdata   calculations   and   is   the interface to the KLN 90B GPS receiver. (3)   The    Display    &    Key    Recorder.        The Display and Key Recorder is a cabin mounted display that   houses   both   the   key   recorder   equipment   and display interface. (4)   Indicator Light.  An indicator light, labeled ETMS,  is  located  on  the  right  side  of  the  instrument panel below the stormscope.  The  ETMS indicator light illuminates  when  the  ETM  is  recording  data  and  for 10 seconds after the master switch is turned on. c.   Normal    Operations.        When    the    master switch   is   turned   on,   power   is   applied   to   the   ETM causing the  ETMS indicator light to illuminate and the ETM  to  perform  a  self-test.    It  is  vital  that  the  pilot follows    certain    procedures    when    starting    up    and shutting down the aircraft. (1)   When   starting   the   aircraft,   wait   a   full 10 seconds before starting the engines after turning on the  master  switch  to  allow  the  ETM  to  complete  its startup procedures. (2)   If the engines are started before the ETM has  completed  its  startup  sequence,  the  system  will not   record   any   engine   starts.      This   will   result   in inaccurate  cycle  counts,  engine  start  counting,  and trend analysis. (3)   When  shutting  down  the  engines,  wait until  the  gas  generator  speeds  of  both  engines  drop below 10% prior to turning off the master switch. (4)   During aircraft operation, the ETM monitors and records data on the engine and airframe parameters and notifies maintenance personnel when the     established     limits     of     those     parameters     are exceeded.    This  data  is,  in  turn,  used  for  later  trend analysis.  The ETM has a secure feature that prevents unauthorized  changes  to  the  retained  statistical  data being recorded. Section IV.  FUEL SYSTEMS 2-41.  FUEL SUPPLY SYSTEM. The   engine   fuel   supply   system,   Figure   2-18, consists of two separate, identical systems, connected by  a  valve-controlled  line,  that  share  a  common  fuel management panel.  Each fuel system consists of five interconnected  wing  tanks,  a  nacelle  tank,  an  engine driven    boost    pump    mounted    on    each    engine,    a standby  fuel  pump  located  within  the  nacelle  tank, a fuel  heater  (engine  oil-to-fuel  heat  exchange  unit),  a tank   vent   system,   a   tank   vent   heating   system   and interconnecting  wiring  and  plumbing.   The  aircraft  are equipped with auxiliary (inboard wing) fuel tanks with a fuel transfer pump located within each tank.