APU

If there is any conflicting information, your FCOM shall be the overriding reference.

Please read the footnote at the end of this page.

Q1. The APU shuts down almost immediately after coming up to speed and the shutdown is accompanied by a FAULT light in the Master switch P/B, an ECAM, and a single chime. What are possible causes for such shutdown?

A1.  The possible causes for such shutdown are:-

(a)   Fire (on ground only)

(b)   Air inlet flap not open

(c)    Over speed

(d)   No acceleration

(e)   Slow start

(f)    EGT over temperature

(g)   No flame

(h)   Under speed

(i)     Reverse flow

(j)     Low oil pressure

(k)   High oil temperature

(l)     DC power loss. (BAT OFF when aircraft on batteries only)

(m) ECB failure

(n)   Loss of over speed protection

Q2. In flight, a dual bleed fault occurs. The QRH procedure directs use of the APU for a bleed source. What is the maximum altitude for APU bleed operations?

A2.  FL200.

Q3. What are the altitude limits for APU generator?

(a)     What is the max altitude up to which electrical power from APU can be used?

(b)    What is the maximum altitude the APU can be used to run two packs?

(c)     What is the maximum ALT up to which APU can be used to run single pack?

(d)    What is the max altitude the APU can be used to start an engine?

A3.  (a)  FL250

For (b), (c) and (d) refer table below

MAXIMUM ALTITUDE FOR BLEED AIR AND GENERATOR LOAD IN FLIGHT

TEMP à

MAX ALT

ISA

ISA+20

ISA+35

ENG START UPTO 20,000 FT

92 %

64 %

45 %

ONE PACK UPTO 22,500 Ft

78 %

67 %

63 %

TWO PACKS UPTO 15,000 Ft

100 %

79 %

64 %

 

Q4. Can the APU be started and operated even if LOW OIL LEVEL ECAM advisory is displayed?

A4.  If there is no Oil Leak, the remaining oil quantity allows normal APU operation for about 10 hours.

Q5. What are the APU parameters that are shown on APU ECAM page?

A5.  Following parameters are shown on the APU ECAM page:-

(a)    APU Bleed air pressure

(b)   APU GEN load

(c)    APU GEN Voltage

(d)   APU GEN Frequency

(e)   APU N%

(f)    APU EGT

Q6. With the APU, can you use Wing Anti-ice?

A6.  No.

Q7. What are the differences between “APU fire on ground” and “APU fire in AIR”?

A7.  The difference between the two situations is that in the first case, the APU shuts down automatically.

Q8. With battery power only, if you do APU fire test, what are the indications?

A8.  The following are the indications:-

(a)    APU FIRE P/b illuminated RED

(b)   SQUIB and DISCH light illuminated

Q9. If EXTERNAL POWER were powering the aircraft, what indications would be seen during an APU fire test?

A9.  The following are the indications:-

(a)    APU FIRE P/b illuminated RED

(b)   SQUIB and DISCH light illuminated

(c)    Mater Warning comes on

(d)   CRC aural Chime

(e)   APU FIRE Warning on E/WD

(f)    APU Page on SD called

Q10. There are two types of ECAMS for APU shut down. One is APU AUTO-SHUTDOWN and other is APU EMER SHUT DOWN. What are the differences?

A10.  APU SHUT-DOWN ECAM comes on in case of Auto shut down of the APU for a reason other than an APU fire whereas an APU EMER SHUT-DOWN comes on in case of :-

(a)    An APU fire is detected on the ground

(b)   The ground crew shuts down the APU manually by pushing the APU SHUT OFF p/b on the nose gear interphone panel

(c)    Flight crew presses the APU fire P/b in the Cockpit

Q11. Will the APU Auto Shutdown for Low Oil pressure?

A11.  Yes.

Q12. When an APU auto shut down has occurred, what other indications are received in addition to the ECAM procedure?

A12.  In addition to the ECAM procedure, the FAULT light on the APU Master S/w comes on.

Q13. How many APU fire extinguisher bottles are installed?

A13.  One.

Q14. After depressing the APU MASTER p/b, the START p/b is pressed. At this time the START p/b illuminates Blue. What does that mean?

A14.  The Blue light in the START P/b indicates that the APU is starting.

Q15. What is the significance of an illuminated FAULT on the APU MASTER SW?

A15.  The illuminated FAULT light on the APU MASTER S/w indicates that an automatic APU shutdown has occurred.

Q16. When would the APU MASTER SW p/b FAULT light illuminate?

A16.  The APU MASTER S/w FAULT light will illuminate in the following cases :-

(a)   Fire (on ground only)

(b)   Air inlet flap not open

(c)    Over speed

(d)   No acceleration

(e)   Slow start

(f)    EGT over temperature

(g)   No flame

(h)   Under speed

(i)     Reverse flow

(j)     Low oil pressure

(k)   High oil temperature

(l)     DC power loss. (BAT OFF when aircraft on batteries only)

(m) ECB failure

(n)   Loss of over speed protection

Q17. What happens when you select APU MASTER SW to ON?

A17.  The following happens when the APU MASTER S/w is selected ON:-

(a)    The blue ON light comes on.

(b)   Electric power goes to the APU system; the ECB performs a power-up test.

(c)    The APU air intake flap opens

(d)   The APU fuel isolation valve opens

(e)   If no fuel tank pump is running, the APU fuel pump operates.

(f)    If the aircraft has ground power or main generator power, the APU page appears on the ECAM display.

Q18. What happens when you select the APU MASTER SW to OFF?

A18.  The following happens when the APU MASTER S/w is selected OFF:-

(a)    The ON light on the MASTER SW P/b S/w, and the AVAIL light on the START P/b, go out.

(b)   The APU keeps running for a cooling period of 120 s at N 100 % speed

(c)    At 7 % the air inlet flap closes.

Q19. When does the START switch ON light extinguish?

A19.  The ON light on the START S/w extinguishes 2 s after N reaches 95 %, or when N is above 99.5 %.

Q20. What is the meaning of the green AVAIL light in APU START p/b?

A20.  The green AVAIL in the Start p/b shows that the APU is available for use and power is OK. It comes on when N is above 99.5 % or 2 s after N reaches 95 %.

Q21. What is the max altitude to start the APU on batteries?

A21.  FL250.

Q22. You arrive to parking stand after landing and start APU but it gets auto shutdown and you need to start it again. What is the APU Starter limit? How many start attempts can be made?

A22.  The APU starter Limitations state that after 3 starter motor duty cycles, one has to wait for 60 minutes for 3 more cycles.

Q23. After landing, during “Securing the Aircraft” Checklist, the APU is shut down and SOP asks you to wait until APU flap is fully closed before switching BAT 1& 2 to OFF. Why?

A23.  Switching the batteries off before the APU flap is closed may cause smoke in the cabin during the next flight. Moreover, the batteries provide APU Fire extinguishing while the APU is running.

Q24. How long will it take for the APU flap to fully close?

A24.  The air intake flap closes fully in approximately 20s.

Q25. If batteries are off while APU is running, what happens to APU FIRE protection system?

A25.  If the batteries are off while the APU is running, APU Fire extinguishing is not available.

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6 thoughts on “APU”

  1. Q2) FL 200 for APIC 3200 and Garrett (Honeywell) GTCP 36-300 APU and FL 225 for Allied Signal(Honeywell) 131-9 APU

    Q16) A16 list is correct for APIC 3200 APU.

    In case of Honeywell 131-9 in addition to the list given in A16 the following will also lead to fault light : Oil system shutdown, Inlet overheat, Clogged oil filter and Loss of EGT thermocouples.

    Garret GTCP 36-300 : A16 list and Overcurrent, Sensor failure and IGV failure.

    Q18) Cooling period is 120 sec at 100% N for APIC 3200 APU. For Honeywell 131-9 it is 60 sec and for Garret GTCP 36-300 it is 60-120 sec at 75% N.

  2. If APU FIRE BOTTLE DISCHARGE THEN WHAT COLOR APPEAR ON DISK?

  3. Abhishek Singh said:

    Can anyone clarify me the case when master switch of APU is left on with BAT 1 & 2 OFF and aircraft is dead.

  4. THE DISK IS RED

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