(c)
Make a record of these parameters on the data sheet.
1) Cabin rate of change
2) Bleed source
3) Duct pressure
4) N2%
(d)
Inspect the right side of the airplane for air leakage while the left engine is in operation.
(10)
Do this check of the left pack capability to pressurize the passenger cabin with left engine at 65% N2:
(a)
Advance the left engine throttle to 65% N2.
(b)
Make a record of these parameters on the data sheet.
1) Cabin rate of change
2) Bleed source
3) Duct pressure
4) N2%
(c)
Adjust the aft outflow valve to stabilize the cabin pressure to 4.0 PSID.
(d)
If 4.0 psid cannot be maintained, refer to the troubleshooting to determine if there is a pack (air inflow) problem and/or an air leakage problem.
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C. Airplane Leak Down Check
(1) Do this check of the leakage of the cabin pressure:
(a)
Make a record of the cabin temperature.
(b)
Adjust the aft outflow valve to stabilize the cabin pressure to 4.5 PSID.
(c)
When 4.5 psid on the DIFF PRESS gauge has been achieved and stabilized, fully close (manually) the aft outflow valve. 1) Make sure that the indication on the gauge above the CLOSED/OPEN switch on
the pressurization control panel shows that the valve is fully closed.
(d)
Set the L PACK switch to OFF.
(e)
Set the BLEED 1 switch to OFF.
(f)
Shut down the left engine.
CAUTION: THE APU MUST BE KEPT IN OPERATION IN THE EVENT A BLEED SOURCE IS NEEDED IF A VERY HIGH RAPID CABIN DEPRESSURIZATION OCCURS OR IF ELECTRICAL POWER IS NEEDED AND A GROUND SOURCE IS NOT USED. FAILURE TO KEEP THE APU IN OPERATION COULD POSSIBLY RESULT IN EQUIPMENT DAMAGE.
(g)
Continue to operate the APU
(h)
Make a record of the pressure differential indications during the cabin pressure leak down: 1) Start the check at 4.0 psid (time zero). 2) Make a record of the pressure differential indications at 10 second intervals for
120 seconds of time.
(2)
Depressurize the airplane and restore it to its unpressurized condition (Ref 5-51-91 MP).
(3)
Remove pneumatic pressure.
(4)
Remove the nose and main landing gear safety locks (Ref 32-00-01 MP).
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D. Performance Summary
(1)
Best performance of the air conditioning packs and airplane structure is as follows:
(2)
If the test data agrees with the best performance data for the packs (inflow) and the airplane structure (outflow), you can be very sure that cabin pressure can be maintained at cruise (FL250) on a single pack.
(3)
Compare the data that you recorded on Figure 202 with the listed best performance data to find the condition of the packs and the airplane.
(4)
If the test data does not agree with the best performance data for the packs and the airplane structure, refer to troubleshooting analysis and steps to correct the problems.
SYSTEM BEST PERFORMANCE
Single Pack - Ground Idle Able to maintain or increase cabin differential at 4.0 PSID and cabin rate of change of 0 or negative value (cabin pressurizing).
Single Pack - 65% N2 Able to maintain or increase cabin differential at 4.0 PSID and cabin rate of change of -500 feet/minute or greater (cabin pressurizing).
Cabin Leakage Rate (4.0 psid down to 2.5 psid) Greater than 100 seconds required for cabin bleed down to occur.
