TM  1-1500-204-23-1 NOTE Precautions  should  be  taken  to  ensure  that these parking area extinguishers are periodi- cally inspected and adequately marked to ensure high visibility (for ease of location in the event of an emergency and to prevent accidents during aircraft movement). Due to the smaller size of the Halon 1211 portable- type extinguishers, these bottles should be secured in a permanent location to facilitate recognition and prevent damage to the extin- guisher. i.  Ground  Receptacle  Testing. Test ground recep- tacle using the following procedures: (1) Using an ohmmeter, check resistance from the receptacle to a point on the aircraft skin adjacent to the receptacle. Contact point used must be free of paint and  corrosion  and  cleaned  for  good  electrical  contact.  An ordinary ohmmeter set on R x 1 scale, will read a direct short or not more than 1 ohm. (2) If resistance reading exceeds requirement of paragraph (I), receptacle must be removed and air- craft skin around it must be cleaned of paint and corro- sion and treated per TM 55-1500-345-23. Reinstall the receptacle in accordance with MIL-C-83413/ MIL-C-8349. Nut must be tight. (3) Recheck ohmmeter reading as in step(1). If it does not meet requirement, repeat procedures (4)   Retouch   paint   as   required   per   TM 55-1500-345-23. g. Aircraft Fuel Port Testing. Test aircraft fuel port ground using the following procedures. (1) Use multimeter, TS352B/U, to check the resistance of aircraft fuel port to the skin adjacent to the fuel port. The contact on the fuel port and aircraft skin should be free of paint and corrosion for a good electrical contact. (2) Set the multimeter on the RX1 scale. If the measured resistance is greater than 1 OHM, the aircraft fuel port must be removed. The aircraft skin around the fuel port must be cleaned of paint, corrosion and then treated  in  accordance  with  TM  55-1500-345-23.  Rein- stall  fuel  port  in  accordance  with  the  applicable  TM 55-1500-345-23 aircraft maintenance manual. (3) Recheck  OHM  reading  as  stated  in  para- graph  3-4g(1).  If  it  does  not  meet  requirement,  repeat procedure. (4) When  a  satisfactory  measured  resistance has been reached, touch-up paint as required per TM 55-1500-345-23. 3-5. Aircraft Refueling. Servicing  aircraft  with  fuel and  defueling  aircraft  requires  the  utmost  precaution  due to  the  highly  flammable  characteristics  of  fuel.  Personnel performing fueling and defueling operations must be thoroughly familiar with FM 10-68, Aircraft Fueling, and FM 10-69, Petroleum Supply Point Equipment and Operations. Personnel must also be completely familiar with the aircraft being serviced. NOTE Aircraft shall have all fuel cells fully serviced prior to being parked or stored in a hangar. All fuel cells should be full in order to minimize the presence of flammable vapors within fuel cell (for safety purposes) and additionally to minimize  water  condensation  and  subse- quent microbiological growth which results in contamination of the fuel. This procedure should be adhered to at all times;  except  when  impending  mission requirements  shall  necessitate  a  reduced  fuel load or when an aircraft shall require mainte- nance to the fuel system. a. Open-Port Refueling. Open-port refueling is refueling  by  inserting  an  automotive-type  nozzle  into  a  fill port  of  larger  diameter.  Most  of  the  Army  fueling  nozzles are designed for open-port refueling and must be used until  enough  FARE  systems  are  deployed  to  make  open- port aircraft refueling an obsolete practice. Because the port  is  larger  than  the  nozzle,  fuel  vapors  can  escape through the fill port during open-port refueling opera- tions. Airborne dust and dirt, as well as rain, snow, and ice can get into the fill port during refueling, thus lowering the quality of the fuel in the tanks and endangering the aircraft. Spills from overflowing tanks are possible in open-port refueling. Spills can also be caused by the sudden pressure surge that comes when pumping from another nozzle in the system is completed, throwing the whole pressure of the pump to the operating nozzle. Because  of  these  dangers,  hot  refueling  by  the  open-port method is restricted to combat or vital training or testing use. Refer to FM 10-68. Change 2 3-9