(h) Descending 

When the ship is descending, air must be fed into the system to maintain the differential pressure between the inside of the envelope and the increasing atmospheric pressure. The scoops should be opened wide enough to per› mit adequate air flow. The air scoops, ducts, and damper valves can admit air into the ballonets at a sufficient rate to maintain a gas pressure of 1.25 inches of water when the ship is descending at a rate of 1200 feet per minute, at a forward speed of 50 knots. 

The air intake capacity naturally decreases as the forward speed is reduced so that the maximum permissible rate of descent is less than 1200 feet per minute when the forward speed is less than 5.0 lrnots. 

CAUTION: 1200 feet per minute is the maximum permissible rate of descent. The actual rate of descent should be kept well below this value. 

(i) Landing 

At the time of landing it _usually becomes necessary to throttle down the motors and the air scoop system can no longer supply the required pressure to the ballonets. An auxiliary blower is provided for such conditions. 

The blower is of sufficient capacity to maintain a gas pressure of 0.5 inches of water at the gas manometer 

