NOTE: The alternate static system drain fitting is found on
____ the right side of the E1 rack.
 (c)  Open the static cut off valve.
 D. The Alternate Static System (Low-Range) Leak Test
 S 865-283
 CAUTION: MAKE SURE THAT THE PITOT LINE PRESSURE IS EQUIVALENT OR MORE
_______ THAN THE STATIC LINE PRESSURE. KEEP THE STATIC PRESSURE CHANGE BELOW 5000 FEET FOR EACH MINUTE. MAKE SURE THAT THE DIFFERENTIAL PRESSURE STAYS BETWEEN 0 AND 10.00 INCHES OF MERCURY. YOU CAN CAUSE DAMAGE TO THE PITOT-STATIC SYSTEM.
 (1)  Apply a vacuum to the alternate static system equal to 5,000 feet of altitiude above field elevation (ambient pressure minus
 5.25 |0.25 in. Hg).
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737-300/400/500MAINTENANCE MANUAL
 S 865-285 CAUTION: HOLD THE VACUUM, AS AN ALTERNATIVE, BEHIND THE CUTOFF VALVES
_______ DURING THE CUTOFF TIME. YOU CAN CAUSE DAMAGE TO THE EQUIPMENT WHEN YOU OPEN THE CUTOFF VALVES WITHOUT THE VACUUM.
 (2)  
Close the static cutoff valve to the system when the necessary altitude is reached.

 S 865-287

 (3)  
Stop for 5 to 6 minutes to permit the system to become stable. S 865-288

 (4)  
Write the altitude.
 S 865-289

 (5)  
Stop for one minute and read the altitude again.
 S 865-290

 (6)  
Make sure that the altitude does not decrease by more than 80 feet

 (0.07 in. Hg).
 S 865-291 CAUTION: MAKE SURE THAT THE PITOT LINE PRESSURE IS EQUIVALENT OR MORE
_______ THAN THE STATIC LINE PRESSURE. KEEP THE STATIC PRESSURE CHANGE BELOW 5000 FEET FOR EACH MINUTE. MAKE SURE THAT THE DIFFERENTIAL PRESSURE STAYS BETWEEN 0 AND 10.00 INCHES OF MERCURY. YOU CAN CAUSE DAMAGE TO THE PITOT-STATIC SYSTEM.
 (7)  Open the static cutoff valve and return the alternate static system to ambient pressure.
 NOTE: You must release the vacuum from the cutoff valves slowly.
____
 E.  Put the Airplane to Its Usual Condition
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 S 085-294 CAUTION: DO NOT DISCONNECT THE PNEUMATIC TEST SET WHEN THE PITOT-STATIC
_______ SYSTEM IS NOT AT AMBIENT PRESSURE. YOU CAN CAUSE DAMAGE TO THE EQUIPMENT.
 (1)  Disconnect the pneumatic test set from the drain fitting.
 S 085-345 WARNING: FAILURE TO REMOVE VINYL ADHESIVE TAPE FROM STATIC PORTS BEFORE
_______ FLIGHT MAY CAUSE LARGE ERRORS IN AIRSPEED SENSING AND ALTITUDE SENSING SIGNALS, WHICH MAY LEAD TO LOSS OF SAFE FLIGHT.
 CAUTION: MAKE SURE THAT YOU REMOVE ALL OF THE PIECES OF TAPE FROM EACH
_______ STATIC PORT. THE SYSTEM WILL NOT OPERATE CORRECTLY WHEN THE TAPE IS IN ITS POSITION.
 (2)  
Remove the vinyl adhesive tape from the left and right alternate static pressure ports.

 S 215-298

 (3)  
Examine the alternate static ports for unwanted materials and rough locations on the inner and outer surfaces (Ref 34-11-11/601).

 S 865-299

 (4)  
Remove electrical power if it is not necessary (Ref 24-22-00/201).

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737-300/400/500MAINTENANCE MANUAL
 PITOT-STATIC SYSTEM - DESCRIPTION AND OPERATION
_______________________________________________
General
_______
 A.  The pitot-static system provides dynamic (pitot) and ambient (static) air pressures to connected airplane equipment and instruments. These pressures are used to determine airplane altitude, airspeed and mach number.
　
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