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GENERAL ENGINE BLEED Fokker 50 - Bleed Air System Page 1

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					                              Fokker 50 - Bleed Air System




GENERAL

Bleed-air is used for airconditioning, pressurization, airframe and engine air intake de-icing,
and for pressurizing the hydraulic tank. Bleed-air is supplied by the engines.

For aircraft equipped with APU
On the ground bleed-air can be supplied by the APU for air conditioning.



ENGINE BLEED

Tappings
Bleed-air is obtained via tappings on each engine, referred to as Low-Pressure (LP) bleed
and High-Pressure (HP) bleed. LP-bleed is normally in use during flight. HP-bleed will be
used at idling and low engine speeds, when LP-bleed is insufficient. The HP-bleed valve will
open automatically provided the BLEED push button, located at the AIR CONDITIONING
panel, is blank. Bleed-air from the HP-Bleed is prevented from flowing into the LP-bleed by a
check valve.

Duct leak detection
A duct leak between the engine tappings and the firewall, resulting in a significant leakage of
bleed-air, is monitored by the engine fire detection and warning system.

Distribution
Bleed-air from both engines is used to supply the following services:
• Airframe, and engine air intake de-icing, see ICE AND RAIN PROTECTION
• Hydraulic tank pressurization, see HYDRAULIC SYSTEM.
• Airconditioning and pressurization, see below.
• If mentioned in aircraft system deviation table:
  Watertank pressurization, see AIRCRAFT GENERAL.




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                              Fokker 50 - Bleed Air System




BLEED AIR FOR AIRCONDITIONING

Supply
Controls and indicators are located at the AIRCONDITIONING panel. Bleed-air is available
when the engines are running and the BLEED push buttons are blank. When a BLEED push
button is depressed to OFF, the Pressure Regulating/Shut-Off valve (PR/SO) and the HP-
bleed valve close. At flight altitudes up to 10.000 feet the supply of bleed-air ceases
completely when the propeller of an engine autofeathers. The above also applies when an
engine has been shut down manually, provided that:
• The POWER lever of the operative engine is at take-off position, and
• Either - TO or GA is selected at the Engine Rating Panel (ERP), or the landing gear is
   extended.

NOTE:           • When a PR/SO valve is closed, a VALVE CLOSED light illuminates
                  independent of BLEED push button indications.
                • FLEX (FLX) is either not used or not installed.

Pressure control
There are three modes of pressure control:
• Normal
• Economy (reduced pressure)
• Augmented (increased pressure)

Normal and ECONOMY can be selected manually. However, for reasons of performance the
economy mode is activated automatically when take-off power is selected and both
airconditioning packs are operative. The augmented mode is activated automatically when
one of the airconditioning packs is switched off manually.

Bleed faults
• Overpressure
  If either PR/SO valve should fail in the open position, the rise in pressure may be sufficient
  to activate a pressure switch. Consequently the relevant BLEED FAULT light illuminates.
• Overheat
  The ducts downstream of the PR/SO valves incorporate temperature switches. An
  activated switch will result in the closure of the relevant HP-bleed and PR/SO valves. In
  addition, the relevant BLEED FAULT light illuminates.
• Bleed-air leakage
  A duct leak between the PR/SO valve and the airconditioning packs is detected by
  temperature switches. An activated switch will result in the closure of relevant HP-bleed
  and PR/SO valves. In addition, the relevant BLEED FAULT light illuminates. If leakage of
  bleed-air is detected around the common duct to the airconditioning packs, the HP-bleed
  and PR/SO valves in both bleed-air systems close.

NOTE:           When either of the PR/SO valves is closed, the supply of bleed-air is
                adequate for continued normal operation.




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                             Fokker 50 - Bleed Air System




FOR AIRCRAFT EQUIPPED WITH APU

APU Bleed

APU bleed-air will be available approximately two minutes after stabilized APU operation; the
AVAIL light at the APU BLEED push button will illuminate.

Depressing the push button from AVAIL to ON will open the APU PR/SO valve to provide
bleed-air to the airconditioning system.

The APU bleed-air airflow can be reduced by depressing the ECONOMY push button at the
AIRCONDITIONING panel to ON.

At lift-off, the APU shuts down (if running) and the APU PR/SO valve will close automatically.
If bleed-air leakage is detected the APU PR/SO valve closes and the AVAIL light goes out. If
an APU PR/SO valve failure is detected an APU FAULT is presented and the APU shuts
down.




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                                Fokker 50 - Bleed Air System




Functional diagram




Functional diagram - For aircraft not equipped with APU




                                              Page 4
                               Fokker 50 - Bleed Air System




For aircraft equipped with apu




Functional diagram - For aircraft equipped with APU




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                          Fokker 50 - Bleed Air System




Controls and indicators




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                          Fokker 50 - Bleed Air System




For aircraft equipped with APU




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                           Fokker 50 - Bleed Air System




 ALERTS



CONDITION(S) / LEVEL         AURAL    MWL/MCL         CAP   LOCAL




 ENGINE BLEED FAULT                                          FAULT
                      1




                                                             BLEED



 ENGINE BLEED FAULT                                          FAULT
 + OTHER ENGINE       2
 PR/SO VALVE CLOSED
                                        CAUTION




 For aircraft equipped with APU



 APU PR/SO VALVE
 FAILURE               2
                                                             FAULT
                                        CAUTION




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