TM 55-1510-219-10 5-9. AUTOPILOT LIMITATIONS. a. An  autopilot  preflight  check  must  be  conducted and  found  satisfactory  prior  to  each  flight  on  which  the autopilot is to be used. b. A  pilot  must  be  seated  at  the  controls  with  the seat belt fastened when the autopilot is in operation. c. Operation  of  the  autopilot  and  yaw  damper  is prohibited  during  takeoff  and  landing,  and  below  200 feet    above    terrain.        Maximum    speed    for    autopilot operation is 247 knots/0.47 Mach. d. During  a  coupled  ILS  approach  do  not  operate the propellers in the 1750 to 1850 RPM range. 5-10.  FUEL SYSTEM LIMITS. NOTE Aviation gasoline (AVGAS) contains a form of lead which has an accumulative adverse effect on gas  turbine  engines.    The  lowest octane AVGAS available (less lead content)  should  be  used.    If  any AVGAS is used the total operating time must be entered on DA Form 2408-13. a. Operating Limits.  Operation with FUEL PRESS light on is limited to 10 hours.  Log FUEL PRESS light on time on DA Form 2408-13.  One standby boost pump may  be  inoperative  for  takeoff.  (Crossfeed  fuel  will  not be available from the side with the inoperative standby boost   pump.)   Operation   on   aviation   gasoline   is   time limited   to   150   hours   between   engine   overhaul   and altitude  limited  to  20,000  feet  with  one  standby  boost pump  inoperative.    Crossfeed  capability  is  required  for climb, when using aviation gasoline above 20,000 feet. b. Fuel  Management.    Auxiliary  tanks  will  not  be filled for flight unless the main tanks are full. Maximum allowable fuel imbalance is 1000 lbs.  Do not take off if fuel quantity gages indicate in yellow   arc (less than 265 lbs.    of  fuel  in  each  main  tank).  Crossfeed  only  during single engine operation. c. Fuel System Anti-Icing. Icing inhibitor conforming   to   MIL-I-27686   PRIST   will   be   added   to commercial fuel, not containing an icing inhibitor, during fueling operations, regardless of ambient temperatures. The   additive   provides   anti-icing   protection   and   also functions as a biocide to kill microbial growth in aircraft fuel systems. 5-11.  BRAKE DEICE LIMITATIONS. The following limitations apply to the brake deice system: a. The brake deice system shall not be operated at ambient temperatures above + 15°C. b. The  brake  deice  system  shall  not  be  operated longer   than   10   minutes   (one   timer   cycle)   with   the landing gear retracted. If operation does not automatically  terminate  approximately  10  minutes  after gear retraction, turn the brake deice switch OFF. c. Maintain  85%  NI  or  higher  during  simultaneous operation of the brake deice and surface deice systems. If adequate pneumatic pressure cannot be provided for simultaneous  operation  of  the  brake  deice  and  surface deice systems, turn OFF the brake deice system. d. In   order   to   maintain   an   adequate   supply   of systems  pneumatic  bleed  air,  the  brake  deice  system shall be turned OFF during single engine operation. 5-12.  PITOT HEAT LIMITATIONS. Pitot  heat  should  not  be  used  for  more  than  15 minutes while the aircraft is on the ground. 5-13.  PNEUMATIC SURFACE DEICE SYSTEM LIMITATIONS. The pneumatic surface deice system shall not be operated at ambient temperatures below -40'C. 5-5