I.  If the 737 airplane exhibits excessive cabin to ambient leakage per MM 05-51-91, then it is recommended that the following tests or checks be performed.
NOTE:  Several small leakage areas may contribute to create an excessive fuselage leakage rate. Therefore, it is recommended that all sources of leakage be repaired.
(1)  
Perform forward outflow valve test per MM 21-43-11 par. 2.D.(1) through (6).

(2)  
Check the following areas for excessive leakage while the airplane is pressurized between 3 and 4 psid.

(a)  
Verify that the EE cooling automatic flow control valve is closed properly. Some EE valves close at approximately 2.5 ± 0.5 psid. Some EE valves close at approximately 0.9 ± 0.5 psid.

(b)  
Verify that the bilge drains located along the bottom centerline of the airplane are closed properly. The bilge drain valves close at approximately 2.0 psid.

(c)  
Check all door and hatch seals for leakage.

(d)  
Check the flight deck windows for leakage.

(e)  
Check the forward outflow valve for leakage.

(f)  
Check the cabin pressure outflow valve seal for leakage.

(g)  
Check the cabin pressure safety relief valves for leakage.

(h)  
Check the cabin pressure negative relief valve seal for leakage.

(i)  
Check the water service panel seals for leakage.

(j)  
Check all air conditioning and APU duct seals at pressure bulkhead penetrations (located in the A/C bay, aft pressure dome, right rear wheel well, and forward pack bays) for leakage.

(k)  
Check the structure in the forward and aft wheel wells for leakage.

(l)  
Check the control cable seals in pressure bulkhead penetrations for excessive leakage.

J.  Areas which are difficult to access may also exhibit leaks.
(1)  Structure hidden by the wing-to-body fairing and the APU bulkhead should be checked for potential structure and seal leaks.
5.  Do the Leakage Rate analysis
A.  Get the correction factor from Fig. 201 and correct the time data for each data point.
NOTE:  You want to use the correction factors with the bleed down time data when the ambient pressure does not equal 14.7 psi and/or the cabin temperature does not equal 70 degrees F.
B.  Plot each time-pressure data point onto the chart shown in Fig. 202.
C.  Draw a best fit straight line through the data points plotted in Fig. 202.
D.  If the plotted line is in the upper zone in Fig. 202, the pressure leakage rate is satisfactory.
6.  Restore Airplane to Normal
A.  Check the restored ASI system for leaks and correct operation if necessary (Ref Chapter 34, Air Data Instruments - Adjustment/Test).
B.  Upon completion of testing, systems and components subject to damage during pressure testing require reactivation or reinstallation and functional testing in compliance with applicable maintenance manual sections.
C.  Remove equipment cooling flow control valve locking device.
May 01/99 5-51-91 Page 202A/202B BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

H17866 T51445
500  Pressure Leakage Test Correction Factor 
May 15/80  Figure 201  5-51-91 
Page 203 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

Pressure Leakage Rate Check Chart  500 
5-51-91  Figure 202  Jun 20/93 
Page 204 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

BRAKE SEIZURE CONDITION - CONDITIONAL INSPECTION
1.  Brake Seizure Condition
A.  Examine main landing gear per the following: 
(1)  
Check axles and brake attachment flanges for cracks. 

(2)  
Check the shock strut for leaks and the drag strut bearings for damage. 

(3)  
Check cadmium plate on mounting flanges and lower torsion links for evidence of blistering and melting. 

NOTE:  On the brake mounting flanges, on the axles in the areas of the brake mounting flanges and on the sleeves, later airplanes have a heat-resistant coating instead of cadmium plate. If cadmium plating has apparently disappeared, it may have vaporized or melted away. Melted cadmium that has fallen off tends to ball up as does mercury. Cadmium that has melted and remained in place after cooling may be blistered, mottled, or wrinkled in appearance. The hydraulic fluid-resistant paint finish will have burned away in most cases. Undamaged cadmium plate has a silver gray color. The heat-resistant coating is recognizable by a greenish gray color. For application of the heat-resistant coating, refer to Chapter 51, Heat, Weather and Oil Resistant Inorganic Protective Coating - Cleaning/Painting.
　
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