Sheaves and Winches Generally  all  sheaves  should  be  free  running, have  no  indication  of  turning  of  the  lips,  or indication  of  jamming  by  terminals.  No  slippage  of the sheave on races should be evident, and any fault of  this  nature  should  be  corrected.  Winches  should be  checked  for  running  and  positioning.  Both sheaves and winches should be kept clean of debris or  foreign  matter,  and  be  regularly  lubricated. BELOW DECKS–THE ARRESTING ENGINE The greatest safety factor in the operation of the arresting engine is constant attention to inspection, maintenance, and overhaul. Preventive maintenance is   particularly   necessary. Daily  inspection, inspection after each arrestment, and depending on the  unit  involved,  inspection  and  maintenance  at regular intervals nullify many of the conditions that might  arise  to  endanger  operating  and  flight personnel. Always keep hands and body clear when engine   is   operating   or   in   a   condition   to   become operable. Weight Selector Settings The safe arrestment of incoming aircraft can be directly  attributed  to  proper  setting  of  the  aircraft weight   selector. Aircraft  weight  selector  settings should always be made according to current aircraft recovery  bulletins.  Maximum  efficiency  is  obtained from  the  arresting  engine  through  proper  weight settings.    There  is  one  distinct  error  in  arrestment that  can  be  directly  attributed  to  improper  weight settings  or  error  in  the  gross  weight  estimate.  This error  results  in  TWO-BLOCKING  the  engine. TWO-BLOCKING  is  a  condition  in  which  the weight  selector  is  set  too  light  for  the  incoming aircraft.  This  condition  causes  the  ram  to  ride forward into the cylinder until the crosshead bangs into   the   mouth   of   the   cylinder.   A   wooden   block assembly,  called  a  ram  block,  is  positioned  at  the crosshead end of the ram to act as a shock absorber by  preventing  metal-to-metal  contact  between  the crosshead  and  the  mouth  of  the  cylinder. BOUNCEBACK is the movement of an arrested aircraft  backward  and  is  caused  by  the  stretch inherent  in  the  purchase  cables.  Bounceback  is desirable  because  the  hook  is  disengaged,  allowing rapid  deck  clearance  for  future  landings.  Pilots  are instructed  to  allow  for  bounceback  before  braking. Control Valve Failure Prime   failure,   with   resultant   disastrous consequences,  could  be  failure  of  the  drive  system that  would  result  in  improper  opening  or  closing  of the  CRO  valve. Cam  alignment  is  equally important,  as  improper  alignment  would  result  in fluid  flow  through  the  CRO  valve  at  a  ratio different from that indicated on the aircraft weight selector  indicator.  Thus,  while  the  operator  would have  an  indication  of  a  proper  setting,  actual  flow control  would  be  different. Drive System Hazards Much  of  the  cable  system  is  contained  behind U-channels  to  protect  personnel  during  operation. This cable, with connections, is subject to wear and fatigue   and   should   be   checked   against   failure. Failure   of   the   drive   system   could   cause   serious injury  to  operating  and  aircraft  personnel. Excessive  Pressures The accumulator is built to take a 400-psi initial charge and such additional pressure as is developed during  arrestment. This  capacity  provides  for  an overloading  factor.    However,  it  is  most  important that   the   accumulator   blow-down   valve   on   the charging  panel  be  kept  open.  Should  leakage  occur from   high-pressure   piping   as   the   result   of inadequate  valving, this,   with   the   additional compression loading during arrestment, could cause an extremely dangerous accumulator pressure. One operating   indication   of   excessive   accumulator pressure  is  retraction  that  exceeds  normal  speed. Initial accumulator pressure must be held at 400 psi. A safety diaphragm is installed on the air side of the accumulator   to   eliminate   the   possibility   of   an accumulator  explosion. Fluid  Level  Indicator  Safety When  the  engine  is  in  BATTERY  position,  the fluid  level  indicator  must  read  BATTERY.  Should any other reading be indicated, the engine must not be  operated  until  a  battery  indication  is  effected. Malfunctions and Safety Personnel   must   always   be   certain   that   their method  of  operation  is  not  responsible  for  a malfunction.  Possible  malfunctions,  causes,  effects, and   remedial   action   are   listed   in   NAVAIR 3-66