(g)
Examine the upper fuselage structure at Body Stations 1000, 1241, and 1480.
C. Put the Airplane Back to It's Usual Condition
S 422-009
(1) Install the components you removed or install replacement
components.
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747-400 MAINTENANCE MANUAL
EXCESSIVE CABIN PRESSURE LEAKAGE CONDITION - MAINTENANCE PRACTICES
__________________________________________________________________ (CONDITIONAL INSPECTION)
________________________
1. General
_______
A. This procedure gives steps to do a leakage test to the airplane fuselage. This leakage test is done to make sure the fuselage pressurized areas are tight and there are no large leaks. The test is not a structural integrity test.
TASK 05-51-08-702-001
2. Excessive Cabin Pressure Leakage Test
_____________________________________
A. General
WARNING: OBEY ALL SAFETY STANDARDS FOR COMPRESSION AND DECOMPRESSION
_______ WHEN PERSONS ARE IN A PRESSURIZED AREA. SUDDEN PRESSURE CHANGES WILL CAUSE PAIN AND INJURY AND MUST NOT BE DONE. WHEN YOU DO NOT OBEY THE PRECAUTIONS, INJURY TO PERSONS WILL OCCUR.
(1)
When persons are in the airplane during this test, they must be in a good physical condition. When a person feels pain during a pressure change, you must lower the pressure or make it stable immediately. Do this to make sure the person can make the pressure equal in their ears. Also, do this to remove the person from the airplane.
(2)
The primary pressure source is the APU. You can also use the engine bleed air, or an external ground source.
NOTE: The external ground source must supply 2500 cfm of air at a
____
pressure of 10 psig.
(3)
It is recommended that an Airspeed Indicator (ASI) be used for this test in place of a pressure gage. However, you can use the standby ASI in pilots' instrument panel.
(4)
Figure 201 shows how to get a correction factor used in connection with the test data. Figure 202 shows the straight line curves for satisfactory airplane leakage rates.
B. Standard Tools and Equipment
(1) Airspeed Indicator (ASI)
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MAINTENANCE MANUAL
HOW TO USE CURVE:
EXAMPLE: (A) 14.15 PSIA, AND TIME THREE MINUTES. ASSUME AVERAGE CABIN TEMPERATURE OF 80`F, AMBIENT PRESSURE OF
(B) PRESSURE CORRECTION FACTOR IS 1.02. THE PRODUCT OF THE TWO FACTORS FROM CURVES BELOW: TEMPERATURE CORRECTION FACTOR IS 0.99, AND
PSIA AVERAGE CABIN TEMPERATURE OF 70`F AND 8.6 PSIG DIFFERENTIAL = IS 1.01. THUS, TIME CORRECTED FOR AN INITIAL AMBIENT PRESSURE OF 14.7
3/1.01 = 2.97 = 2 MINUTES 58 SECONDS.
160
16
120
14
CABIN TEMPERATURE - `F
AMBIENT PRESSURE - PSIA
80
12
40
10
0
8
6
-40
-80
4
THE CORRECTION FACTOR TO BE APPLIED TO THE BLEED DOWN TIME WHEN THE AMBIENT PRESSURE DOES NOT EQUAL 14.7 PSIA AND/OR THE CABIN TEMPERATURE DOES NOT EQUAL 70`F.
Pressure Leakage Test Correction Factor
Figure 201
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MAINTENANCE MANUAL
4
3.5
DIFFERENTIAL PRESSURE - PSI
3
2.5
2
1.5
0 60 120 180 300 360 420 480
TIME - SEC
747-400 PASSENGER (4 PSI LEAKDOWN)
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