TM 1-1510-218-10 5-16 Following  decompression,  the  cabin  pressure  altitude is considered to be the same as the flight altitude. c.   When  flying  at   altitudes  above   25,000 feet, one mask per occupant must be coupled to the oxygen outlet and immediately available C . d.  Oxygen  system  data/duration  tables  may  be found in Chapter 2. 5-36.  CABIN PRESSURE LIMITS. Maximum  cabin  differential  pressure  is  6.1  psi C D T1 6.6. psi  T2. 5-37.  CRACKED CABIN WINDOW/WINDSHIELD. If a crack occurs in a single ply of cabin exterior window, the aircraft is limited to unpressurized flight.  If a  crack  occurs  in  both  outer  and  inner  plies  of  the cabin  exterior  window,  the  aircraft  shall  not  be  flown unless     proper     authorization     is     obtained     for     an unpressurized ferry flight.  If a crack occurs in an outer ply windshield, no action is required in flight.  If a crack occurs in an inner ply windshield or if a crack occurs in either/both plies of a cabin window, refer to emergency procedures in Chapter 9. Section VIII.  OTHER LIMITATIONS 5-38.  PASSENGER SEATS. The  cabin  passenger  seats  may  be  used  in  the forward or aft positions.  The headrest and seat back, when occupied, must be in the fully upright position for takeoff and landing. 5-39.  ILS LIMITS. During   an   ILS   approach,   do   not   operate   the propellers in the 1750 to 1850 RPM range. 5-40.  INTENTIONAL ENGINE CUT SPEED. In-flight  engine  cuts  below  the  safe  one-engine inoperative speed of V_sse, 104 KIAS are prohibited. 5-41.  LANDING ON UNPREPARED RUNWAY. CAUTION Operation  on  unimproved,  soft,  or  rough surfaces  is  recommended  only  for  aircraft equipped with high floatation landing gear. CAUTION Except in an emergency, propellers should be moved out of reverse above 40 knots to minimize     propeller     blade     erosion,     and during     crosswind,     to minimize stress imposed on propeller, engine and airframe. Care shall be exercised when reversing on runways  with  loose  sand  or  dust  on  the surface. Flying gravel will damage propeller  blades  and  dust  may  impair  the pilot’s   forward   visibility   at   low   airplane speeds.      The   aircraft   has   demonstrated landings on hard, smooth surfaces and dry sod  runways.    Hard  braking,  i.e.,  skidding tires while operating on other than smooth surfaces,    can    result    in    damage    to    the landing gear.  When landing on other than dry   surfaces,   use   discretionary   propeller reverse     to     stop     the     airplane     on     the available runway. 5-42.  MINIMUM    OIL    TEMPERATURE    REQUIRED FOR FLIGHT. CAUTION Anti-icing additive must be properly blended with the fuel to avoid deterioration of the fuel cell.  The additive concentration by volume shall be a minimum of .06% and maximum  .15%.    Approved  procedure  for adding  anti-icing  concentrate  is  contained Chapter 2, Section XII.