(g)
Low acceleration rate: When the APU speed fails to maintain 0.1% per second rate of acceleration, acceleration failure will only be invoked after 5% speed and combustor light off has been achieved.
(h)
Deceleration during start sequence: This occurs during engine speed deceleration at a rate greater than or equal to 1.6% per second for 3 consecutive seconds.
(i)
Surge/Reverse Flow Reverse flow APU shutdown occurs when the load compressor delta P/Ps drops below the minimum acceptable limit when the surge control algorithm has commanded the bleed control valve to the maximum surge free position.
(j)
Generator high oil temperature APU shutdown occurs when the generator oil temperature RTD detects an oil temperature above 365 deg.F (184.99 deg.C)
(k)
Loss of DC power APU shutdown occurs when a voltage of less than 15.5VDC for more than 230 m secs is detected at the ECB power supply.
(l)
Underspeed APu shutdown occurs when the APU speed drops below 95% after establishing a ready to load condition.
(m)
Loss of speed
APU shutdown occurs if both speed sensors fail.
(n)
Sensor failure
APU shutdown occurs after the following failures:
both thermocouples, or
both oil temperature RTDs, or
low oil pressure switch and oil level RTD, or
low oil pressure switch and low oil level.
(o)
Air intake not open APU shutdown occurs if the air intake actuator (4015KM) fails with the air intake flap in the not fully open position.
(p)
ECB failure APU shutdown occurs when the following failures in the ECB are detected. Backup overspeed circuit failure, both speed injection test failure.
(2) Alternate values for failed sensors The ECB 59KD programmes alternate values for certain failed LRUs to keep the APU availiable. The LRU failures and alternate actions are listed as follows: ------------------------------------------------------------------------------
FAILED LRU ACTION ------------------------------------------------------------------------------Gearbox oil temperature For high oil temperature shutdown a generator
oil temperature greater than 320 deg.F (160 deg.C) has to be detected.
Generator oil temperature In the event of sensor failure, the generator is still protected by the gearbox high oil temperature limit.
Inlet air temperature For fuel adjustments, the following default values are used: Max fuel limit: T inlet = -65 deg.F (-54 deg.C),
P inlet = 14.7 psia. Min fuel limit: T inlet = 50 deg.F (10 deg.C), P inlet = 3 psia. For acceleration and EGT set point: P inlet = 3 psia.
PID control gains at steady state speed control: P inlet = 7.3 psia. T inlet = 70 deg.F (21 deg.C).
Cold junction RTD The last cold junction is used if the ECB is powered after failure and no valid cold junction value is available. Default value is 70 deg.F (21 deg.C).
7. Operation/Control and Indication:
_________________________________
(Ref. Fig. 005)
A. APU Start
(1)
Energize the 28VDC battery busbar 301PP and close the subsequent circuit breakers:
-
the ECB SPLY 1KD,
-
the APU CTL 2KD.
(2)
Set the MASTER SW pushbutton switch 14KD to the ON position.
-
the ON legend in the switch comes on,
-
the ECB energizes through the relay APU MAIN 4KD,
-
the ECB starts the power-up test,
-
the APU fuel LP valve actuator 3QF energizes and opens the APU fuel LP valve 14QM,
-
the APU fuel-feed pump element 4QC and control is armed,
-
the air intake flap opens,
-
the start system is energized.
(3)
When the APU START pushbutton switch 2KA is pushed to ON, the ON legend in the switch comes on. The automatic start cycle starts (Ref. 49-42-00).
(4)
When the automatic start cycle ends, the engine reaches governed speed and is ready to load. The ECB transmits an 'AVAIL' signal to the related aircraft systems. When this occurs the ON legend in the APU START switch goes off and the AVAIL light comes on.
(5)
The fine-speed circuit in the ECB and the proportional governers, keep the speed constant at the correct speed. The fine-speed circuit sends a signal to the fuel control unit which increases or decreases the fuel flow as necessary.
Starting - Acceleration Closed Control Loop
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