MD-80 parte 7 - Schemi tecnici 4 - Auxiliary Power Unit (APU)

APU:
Operational limit FL 250
Max temperature 760 C (During start, for 30 Sec)
Max cont. load 630 C
Max transient 663 C
RPM norm 95 - 105 %

RPM caution 105 - 110 % Auto shut off rpm >110 % or oil press <2 Psi
Duty cycle 50 - 70 Sec
Oil Temp Light on 124 C
APU Generator 40 Kva
APU ac load on ground 1,25 (50 Kva)
APU maximum regulation pressure for ac packs 31-40 Psi

Started by dc pwr, bttr switch must be on
On ground: APU supplies ac packs. If pneumatic pressure is below 12 Psi, only one pack operation is allowed
APU is supplied by dc pump (Right Wing), every ac pump of right or centre tank, every pump of left tanks if CROSSFEED open

If in flight no left/right ac pwr is available, open ram air door for windmill start

Tip: Pull CB X 40 and you have pwr from bttr.
On ground no cross tie possible when APU is online
Pull Sensing CB (Behind Cpt.) CB K+L34

In flight: (APU)
Master Caution and Fire Detection Loop Light (Annunciator Panel) illuminated

Quick RHB, TAB 23 ENG/APU FIRE DETECTOR LOOP LIGHT AND LOOP A OR B LIGHT ON WITHOUT FIRE WARNING ...point "TEST INDICATIONS OBSERVE"

Following indications are mandatory:

1. APU Fire Light (Annunciator Panel)
2. Fire detection Loop Light (Annunciator Panel)
3. Master Caution
4. Master Warning
5. Loop Lights (3*) (Overhead Panel)
If all indications are observed, the test is "Satisfactory", further Quick RHB.
If one does not come on, the test is "Unsatisfactory", further Quick RHB.
APU don't have an aural warning. ( one Loop)
Source: System description, Section 4, 8-1-0, Code 3, Page 1/2
When you select the other system (A/B) no visual or acoustic warning has to come on. Otherwise the test failed. The warning bell rings only 3 times

Tip
Situation:
APU doesn't supply any pwr after RESET !

Solution:
Switch of APU . Pull the APU Control CB / Overh. Panel. Push APU Starter and hold.
Reset CB, release APU Starter.
If it doesn't work: wait until one engine is off, RESET APU

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