TM 9-2320-279-10-1 Table 2-1. Preventive Maintenance Checks and Services for Models M977 thru M985E1 Item No. 51.1 Weekly WARNING 52 Weekly 52.1 Weekly Interval could  result. Pintle  Hook Location Item  to Check/Ser- vice Self- Guided Coupler M1977-CBT Crewmember Procedure Check  self-guided  coupler  (1) for  obvious  damage  and  pres- ence  of  the  indicator  lock  (2). (a) Disengage  swivel  lock  (3) and   swivel   self-guided   cou- pler  (1). (b) Engage  swivel  lock  (3). (c)   Open   safety   latch   (2) away  from  hook  lock  (4). (d)   Pull   out   on   hook   lock catch  (5)  and  pull  out  on  hook lock  (4)  to  release  hook  (6). (e) Push  up  on  hook  (6). Not Fully Mission Capable  If: Self-guided   coupler   is damaged  or  loose.  In- dicator  lock  is  missing. Self-guided   coupler does  not  rotate  freely. Keep  fingers  clear  of  top  of  lift-hook  or  injury  to  personnel Rear Spring/ Parking Brake Chambers (f) Close  safety  latch. Check  pintle  hook  for  looseness and/or   damaged   locking   mech- anism  or  locking  pin. Check rear spring/parking brake  chambers  to  ensure  dust covers  are  in  place  and  secure. Pintle  hook  is  loose  or locking   mechanism   and cotter  key  are  damaged and  equipment  is  re- quired  for  mission. Change 5 2-64.1