EXCESSIVE CABIN PRESSURE LEAKAGE - CONDITIONAL INSPECTION
1. General
A. Pressure leakage testing is performed to determine the tightness of the pressurized areas of the fuselage and the rate of leakage from the structure.
B. If personnel are in the airplane during a test, they must be in good physical condition. If any person experiences pain during pressure change, the pressure should be immediately stabilized and lowered until the person can either ventilate his ears or be removed from airplane.
WARNING: OBEY ALL SAFETY STANDARDS FOR COMPRESSION AND DECOMPRESSION. WHEN PERSONS ARE IN A PRESURIZED AREA. SUDDEN PRESSURE CHANGES WILL CAUSE PAIN AND INJURY AND MUST NOT BE DONE. WHEN YOU DO NOT OBEY THE SAFETY PRECAUTIONS, INJURY TO PERSONS WILL OCCUR.
C. Miscellaneous Information
(1)
The APU will be used as the pressurization source for the test. Optionally, engine bleed air or external air source may be used for the pressurization.
(2)
The cabin pressure differential indicator is used for this test.
(3)
Refer to par. 3 for removal of certain system units.
(4)
Figure 201 shows how to obtain a correction factor used in connection with some test data. Figure 202 shows the straight line curves for acceptable airplane leakage rates.
2. Equipment and Materials
A. Stop Watch
B. Bar (suitable to lock the equipment cooling flow control valve)
C. Box end wrench/or common screwdriver
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May 01/98 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 5-51-91 Page 201
3. Prepare for Cabin Pressure Leakage Test
A. Physically lock equipment cooling flow control valve in fully closed position for entire test.
NOTE: Locking equipment cooling flow control valve may be done by using a box wrench to close valve and lockwiring box wrench to available airplane structure or a screwdriver for valves with a screwdriver slot.
B. Remove oxygen system continuous flow control units forward of forward cargo compartment bulkhead and oxygen diluter demand regulators in crew cabin (Ref Chapter 35, Oxygen).
NOTE: Removal of oxygen equipment is not required provided 20 psi absolute is not exceeded.
(1) Make sure you remove the oxygen masks from the stowage boxes.
C. Check pitot static systems for integrity and test pitot static systems per Chapter 34, Pitot Static Systems - MP. All spare air data units and air data units with disconnected pitot static lines must be removed from the airplane and the pitot static lines must be capped. No pressure leakage test should be conducted on an airplane which has not been tested for pitot static systems leaks or blocks unless all air data equipment is removed.
D. Start APU (Ref Chapter 49, Airborne Auxiliary Power Unit).
E. Turn on air conditioning pack (Ref Chapter 21, Air Conditioning). Operate pack in auto at approximately 70°F (21°C).
NOTE: Either the left or the right air conditioning pack may be used.
F. Verify that outflow valve position indicator shows valve to be wide open. FLIGHT/GROUND switch in ground position. Select MAN DC on mode selector switch of pressure control panel selector.
4. Test Cabin Leakage
A. With air conditioning system stabilized, toggle main outflow valve closed. Monitor valve position indicator to see that valve closes. Allow outflow valve to close completely. With forward outflow valve closed, blue light should be on.
B. Record rate of climb indicator reading.
C. Continue pressurizing at maximum or lower rate as desired until cabin pressure differential reaches 4.0 psi on differential indicator.
NOTE: Differential indicator reading should not exceed 4.0 psi during normal test.
D. Turn off the air conditioning pack (Ref Chapter 21, Air Conditioning).
E. Switch off APU (Ref Chapter 49).
F. Make a record of the pressure differential and the time during the cabin bleed down. Start the test at 4.0 psi differential (time zero). Stop the test at 2.5 psi differential.
G. Record a minimum of 4 sets of measurements for each of the following:
(1)
The time on the stopwatch.
(2)
The cabin differential pressure.
H. If the test is to be run again, do a 20 minute cool-down time.
(1) Do this with the equipment cooling fans operating at zero differential pressure.
NOTE: This will make sure the fans will not overheat.
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