Category Archives: AircraftTroubleshooting

F50 N373RR

removed failed #1RTU. INSTALLED SERVICEABLE UNIT.

PARTS OFF: P/N.     S/N

REMOVED FAILED FCP AND INSTLLED REPAIRED UNIT.

PARTS OFF:  P/N 822-0353-02     S/N 166

PARTS ON:  P/N 822-0353-02     S/N

 

 

 

………………….N383RR 12 24 36………………..

 

Hrs 7931.3  Cyc 5385

1. STANDBY STATIC COVER SCRATCHES PAINT, FOAM IS MISSING, M.

 

2. LIGHTS:  L AVIONICS, L MASTER WARN., L MASTER CAUTION ASTRA73, #2 FUEL XFER, R MAP LIGHT,  ANN BELOW LEFT EGPWS, , FSB/NS ALL DA

 

3. SHIELD LIGHT POTENTIOMETER HAS DEAD SPOTS.

 

4. INVALID AC DB. TS MAINTENANCE COMPUTER, RELOAD ACDB.  PROLINE 4 EFIS SYSTEM WILL NOT ENTER TEST MODE.

 

5.  NO AURAL WARN, NO FIRE BELL, TRIM CLACKER, AP DISCONNECT TONE. CHECK TO BE SURE BOX IS PLUGGED IN. WORKS ONLY WHEN SPKR SELECTED ON AUDIO PANEL.

6. 0 CREW TEMP AMPLIFIER FAN NOT RUNNING.  SWAP WITH PAX FOR TROUBLESHOOTING.

7. FSB/NS ALL DARK. NS HAS NO CHIME.

 

 

8. LEFT E-EXIT LIGHTS DEAD

 

9. RIGHT E EXIT FLOUESCENT DEAD.

10. READING LIGHT FWD OF LEFT E EXIIT INOP.

11. VANITY MIRROR HANGS ON FWD DOOR. AFT MIRROR DOOR SLIDES DRAG.

12. LAV BACKREST BLOCKS MIRROR SWINGOUT DOOR.

 

13.  BULB MISSING AT R SIDE VSNITY

14. 1L SEAT NO FOR/AFT TRACK

 

15. FWD VIDEO SELECT INOP, ALWAYS DVD1, AFT VIDEO SELECT INOP, ALWAYS AIRSHOW.

 

16. COPILOTS SEAT LOCK PINS DO NOT LOCK SEAT IN POSITION, REFERENCE SB, AD.

 

17.  RH O2 MASK MISSING TEST BUTTON.

18. IR UNIVERSAL REMOTE FAILED, BATTERIES? REMOVE FROM AC?

19. 3L SEAT ENTERTAINMENT CONTROL FACE PLATE LOOSE, PHONE JACK LOOSE.

20. AFT LEFT AND RIGHT  FUEL SWINGDOWN PANEL DAMAGED BY FLAP FAIRING

21. NOSE TAXI LIGHT MOUNTED OUTSIDE OF BRACKETS, CAUSED TEARS IN RIGHT SIDE NOSE GEAR DOOR SEAL.

 

22. LNLG LATERAL DOOR BONDING STRAP BROKEN

 

23.  RED RUST ON BELLY PANEL HARDWARE ADJACENT TO WING L.E.

24. LEFT WING ROOT FUEL DRAIN WEEPS.

25. RH WHEEL WELL BOLT MISSING ON FWD UPPER TIRE BURST SHIELD

 

26. GRIME COATS ALL THREE LOWER STRUT BARRELS.

27. LEFT FLAP CANOE DRAGS and scratches FLAP  TRACK, SCRATCHING NOISE WHEN FLAP IS EXTENDING. CANOE RIDES ON TRACK FOR THE LAST 1 INCH OF TRAVEL.

 

28. LH RTU  DISPLAYS ATC MODE A CODE, RH RTU DISPLAYS FLIGHT ID.  TEST BOTH DURING FAR CHECKS.

29. PILOT RIGHT RUDDER PEDAL PLASTIC NOT GLUED.

30.  CHECK ECTM, MEMORY FULL.  DOWNLOAD DEECS WHILE ENGINE COWLS ARE OFF?

31.  COPILOT SIDE WINDOW SUNSCREEN UNGLUED AT THE TOP.

 

32.   LISTEN TO AUDIO QUALITY AT CABIN P.A. WHEN HAND MICS IN USE.

 

35. PILOT AND COPILOT EXTENDED SUN SCREEN HAVE NO TRAVEL STOPS.  THEY EASILY PULL FREE FROM THE TRACKS.

 

36. 3RD CREW SEAT NO LATERAL TRACK.

 

37. LEFT WINGTIP STATIC WICK BENT, ALLEN SCREW MISSING?

 

38.  SCREW FWD OF LEFT INBOARD GEAR DOOR SHANKED.

39. SURFACE CORROSION AT RH WINGTIP COMPASS ACCESS DOOR.

40.  LEFT E EXIT SIGN INOP.  NO POWER AT THE WIRES CONNECTED TO PLACARD.

 

41 MAP LIGHT FWD OF LEFT E EXIT BULB HAS BEEN REMOVED.  ADJACENT LIGHT HAS GE305 BULB INSTALLED, SEEMS TOO LONG.

42. NOSE RADOME BOOTY IS ERODED ALL THE WAY TO THE PAINT+ PAINT HAS CRACKS

 

43. Lh aileron SURFACE CORROSION

44. EMERG LIGHT BATTERIES DUE.

LEFT FWD: P/N 60/2505-5 S/N 977

LEFT AFT. P/N D743-02-001 S/N 4370/06-2013

 

RIGHT AFT. P/N D743-02-001 S/N 4368/06-2013

47.  ONE SCREW MISSING AT ANNUNCIATOR PANEL.

48.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

When is the friction check due on a Falcon 50 H stab

 

For F50 N98DH, the fwd H-Stab, (Normal) motor is P/N 1234-2, S/N 206, monted on Stab Jack P/N 021121-09.    S/N 332.

 

Normla motor is p/n 1234-2

 

That means the stab jack is compliant with SB F50-267, and SB F50-247.

So, brake current check and instpect and clean are not due at the 12 month check.

 

Here is some of the early analysis.

PRE SB

you have Stab Jack P/N 021121-01 or 021121-05 or 021121-05 AND Normal motor P/N 1234.

Brake holding check and Check is due at the 12 month AND check and clean is due at the 12 month.

 

POST-SB 147

 

you have any stab jack with stab normal motor p/n 1234-1.Drop out current check  is not required. inspectand clean  is due at every 12 month check.

 

POST S/B F50-267

you have any P/N 021121-09 stab jack, with normal motor 1234-2,  Check and cleaning not required, drop out current not required.

F50 items N98DH

pilot report.

HRS 9950.3

CYC  5311

Yellow HDG miscompare at rotate, and sometimes descent.  Both HDG seem identical, even when HDG CMPRTR warn is present.  Verfied. Rplced #1 ahrs.

#2 AHRS CB pops. Previous troubleshooting found a grounded , burned in two, power wire near fwd RH card cage in the nose. Possibly verified.  Slave control free switch contact burned.  Smoke evedence. (Picture). Repaired wire.

 

Repaired wire at #2 AHRS slaving control panel switch.  #2 AHRS system ops test good I.A.W AMM 34-21-00710

 

Pilot and copilot tx sidetone very loud, cabin sidetone, ics sidetone normal.  Verfied.

 

Adjusted pilot  Audio control box P/N M1045-fbaa-hj7f S/N 9010358, and copilot s/n ,  headphone level, speaker sidetone level, ICS level, and ICS sidetone level I.A.W. AMM 23-50-01-820-801.  Crew ICS system ops checks normal.

 

Ectm 1, needs  download

Number 2 RMI flag flickers into view.  Troubleshot by AHRS swap and STIM. Failure is now pilot RMI.   order AHRS collins AHC85E, P/N 622-6190-204 , failed S/N 726( causes RMI flag to flicker into view.

AHRS swap detail: Units are now swapped to:

#1 unit, Aft. P/N.622-6190-204    S/N 957

#2 unit, Fwd. P/N.622-6190-204    S/N 726 (causes RMI flag to come in view)

Removed failed AHRS computer #1.  Installed overhauled unit.  Unit recieved on Duncan W/O 4K0Y6,  from Regional Avionics Repair WO.    2020-9726.

Parts off:   P/N. 622- 6190-204. S/N 726. (Causes HDG flag to flicker)

Parts on:   P/N. 622- 6190-204. S/N 866.

Unit installed I.A.W. AMM 34-22-01-900-801.  AHRS system #1 ops checks normal.

P.brake bleed down.  Needs troubleshooting.

TERRAIN DISPLAY button inop.

Lh main brace leak, needs troubleshooting.

2 hyd pump bad,2000 psi replace pump. done.

Busstied ann  and other anns , needs bulb.

Crew temp valve resistor dead, passenger has rough spots near full cold. Needs crew dual temp valve.

Wednesday early am.  L ahrs displayfail with original in aft postion, and rh rmi flag in view. R rmi card shakes. Center MFD shows red DRV. This ended up being….AHRS will not STIM with STBY battery breakers in.

 

MFD Red DRV is a problem.  Rerack MFD solved this.

No ALIGN light on MSU.  Replaced with serviceable.

Parts Off.

MSU p/n CG1042AB03. S/N 1084 (align light inop)

 

Parts on:

MSU p/n CG1042AB03. S/N 461 (removed from inservice aircraft, see Pollard Spares LLC  SO5857.  Init ops test good refrence AMM 34-21-00-710-801

 

 

 

 

 

Ann bulbs

#2 hyd qty

Panels at pylon

Window seal

Cabin floor.

Low fuel light

Number 1 dme ind dead.

Left closet avionics fan loud

Terrain display inop.

Why is number 2 dpu 622-9009-001, #1 is -002

 

?——————————–

Week starking June 9

New items:

Left pylon leak

Aft compartment leak

Skin temp thetmostat at rh wheelwell not bonded.

Air check valve left side f4 tape

dv window has jumped the rack and pinion, needs reseal.

#1 and 2 mlg tire condition.

Fuel sample bottle clip brocken.

BATT 1 amps blue lamp inop.

Pilot and copilot window shades need rewind, small glue repair.

Low fuel light on

Hyd qty low

Number 2 transfer light will not go out.

Red CABIN light  rigged on the edge,

MED overserviced, upper fwd seal area gap., fwd side mid to fwd upper corner.  Check rigging also.

 

Dv window jumped off teeth, check stripped bolt.

 

No terrain display.

Ectm 1

 

 

 

 

Pilot reports 30 degree heading split.

98dh left alpha, then 13

Copilot seat no springback in seat lock. Also rocks for/aft

IRU will sometime start with FAN FAIL.

 

 

 

 

July 20, 2020

 

How does the DEEC / Power Increase / Start latch work on a Falcon 900 B?

 

 

DeecSymbolic1

DeecSymbolic2

DeecSymbolic3

f900 Deec 2

F900B 1

ITT Gages with power increase

Start Logic Symbolic

How does the Falcon 900 Start latch work?

 

1.
General
The purpose of the fuel regulation system is to control the quantity of fuel injected into the combustor as a function of the volume of air passing through the engine, whatever the flight conditions (speed, altitude, pressure, temperature, etc…), while maintaining operational safety.
The system comprises:
• the hydromechanical fuel control unit which processes commands received from the electronic engine computer in the normal mode of operation and responds to the power lever position in manual mode,
• the digital electronic computer,
• the surge bleed valve controlled by the computer.
2.
Description
Refer to fig. 3 and fig. 4
A.
Hydromechanical fuel control unit (FCU)
The unit is installed on the same shaft as the fuel pump. Either component can be replaced separately.
The FCU mainly consists of:
• an overspeed governor driven by the pump drive shaft and measuring the speed of the HP spool,
• the power lever shaft which controls a potentiometer and the fuel shut-off valve,
• a P3 pressure limiter (HP compressor outlet pressure),
• a flow regulator receiving P3 pressure and a signal from the computer,
• a torque motor for fuel flow regulation,
• an operating mode selector electric valve (normal/manual),
• an overspeed fuel shut-off valve,
• a maximum thrust adjustment screw for manual mode,
• a sight window for observation of the graduated FCU quadrant.
B.
Digital electronic computer (N2 control) without SB F900-320-R1
Refer to fig. 6 and fig. 5
engine 2 computer is installed in the rear compartment; engine 1 and 3 computers are in the baggage compartment.
The computers are supplied with 28 V DC power, controlled by the “CMPTR” switch (2EP1)/(2EP2)/(2EP3), for A/C < 179) or (L2EP)/(M2EP)/(R2EP), for A/C ? 179) on the overhead panel:
• engine 1 computer is supplied from primary bus “A” (bus “A1”).
• A standby power supply for engine 1 computer is available from bus “B” (bus “B1”).
• engine 2 computer is supplied from primary bus “B” (bus “B1”).
• engine 3 computer is supplied from primary bus “A” (bus A2″).
When a computer is not in operation, indication is given by a “CMPTR” light on warning panel (2WW).
The “CMPTR” switch has three positions: “AUTO”, “MAN” and “OFF”. The normal position is “AUTO”.
In the event of a failure (illumination of “CMPTR” light on warning panel), the “MAN” position can be selected in order to maintain computer power supply and the N1 and N2 overspeed safety systems in manual mode. In this case, the corresponding “CMPTR” light remains on.
NOTE:
On A/C ? 179, the illumination of the “CMPTR 1”, “CMPTR 2” or “CMPTR 3” light causes the illumination of the “MASTER CAUTION” amber lights (L4WW) and (R4WW) simultaneously.
In the “OFF” position, the power supply to the computer is cut off.
Each computer receives the following data:
• power lever position (supplied by the potentiometer),
• air intake pressure and temperature (Pt2-Tt2),
• LP and HP spool speeds (N1 – N2),
• T5 temperature,
• flight/ground signal,
• “PWR INC” at take-off signal.
In addition, each computer can receive signals from the following optional systems:
• N1 or N2 synchronizer,
• APR (Automatic Power Reserve): power increase at take-off if one engine is inoperative,
• PWS (Power Management System): optimization of engine speed in flight through a cruise computer.
Each computer supplies the following signals:
• fuel schedule,
• manual operating mode electric valve control signal,
• overspeed safety electric valve control signal,
• surge bleed valve control signal (two electric valves),
• “CMPTR” warning light triggering signal,
• end-of-starting phase signal.
The front panel of each computer includes the following components:
• Pt2 air intake pressure tube coupling,
• air filter,
• test connector (J2),
• wiring harness connector (J1),
• 11-position function selector switch,
• 4-digit liquid crystal display,
• a panel listing the 12 failure codes which can be displayed,
• a guarded spring-loaded calibration switch.
C.
Digital electronic computer (N1 control) with SB F900-320-R1
Refer to fig. 7 and fig. 5
engine 2 computer is installed in the rear compartment; engine 1 and 3 computers are installed in the baggage compartment.
The computers are supplied with 28 V DC power, controlled by the “CMPTR” switch (2EP1)/(2EP2)/(2EP3), for A/C < 179) or (L2EP)/(M2EP)/(R2EP), for A/C ? 179) on the overhead panel:
• engine 1 computer is supplied from primary bus “A” (bus “A1”).
• A standby power supply for engine 1 computer is available from bus “B” (bus “B1”).
• engine 2 computer is supplied from primary bus “B” (bus “B1”).
• engine 3 computer is supplied from primary bus “A” (bus A2″).
A computer not in operation is indicated by the illumination of a “CMPTR” light on warning panel (2WW).
NOTE:
On A/C ? 179, the illumination of the “CMPTR 1”, “CMPTR 2” or “CMPTR 3” light causes the illumination of the “MASTER CAUTION” amber lights (L4WW) and (R4WW) simultaneously.
In the “OFF” position, the power supply to the computer is cut off.
Each computer receives the following data:
• power lever position (supplied by the potentiometer),
• air intake pressure and temperature (Pt2-Tt2),
• static pressure (Ps0) connected to engine 1 and 3 computers (which are located in pressurized areas),
• LP and HP spool speeds (N1 – N2),
• T5 temperature,
• flight/ground signal,
• “PWR INC” at take-off signal.
In addition, each computer can receive signals from the following optional systems:
• N1 or N2 synchronizer,
• APR (Automatic Power Reserve): power increase at take-off if one engine is inoperative,
• PWS (Power Management System): optimization of engine speed in flight through a cruise computer.
Each computer supplies the following signals:
• fuel schedule,
• manual operating mode electric valve control signal,
• overspeed safety electric valve control signal,
• surge bleed valve control signal (two electric valves),
• “CMPTR” warning light triggering signal,
• end-of-starting phase signal.
The front panel of each computer includes the following components:
• Pt2 air intake pressure tube coupling,
• Ps0 static pressure,
• test connector (J2),
• wiring harness connector (J1).
D.
Surge bleed valve
Refer to fig. 2
This electropneumatic valve enables air bled from the LP compressor outlet to be discharged into the fan duct.
The valve has three positions: “closed”, “1/3 open” and “fully open”. The position is controlled by two solenoid valves (1/3 open, fully open) located in the fan duct shroud and controlled by the electronic computer.
3.
Operation
Refer to fig. 1
A.
Normal engine operation (N2 control) without SB F900-320-R1
The computer performs the following functions:
• conversion of analog input signals into digital signals in order to calculate output parameters, then conversion of these parameters into analog signals corresponding to fuel schedule and the position of the surge bleed valve,
• during starting, regulation of fuel flow, limitation of T5 temperature and automatic starting sequence interruption,
• holding ground or flight idle, when the power lever is set to “idle”,
• limitation of maximum thrust, when the power lever is set to “full power” (in particular, regulation of the “flat rated” thrust according to Pt2/Tt2 conditions),
• N2 power setting regulation, either directly at take-off or idle, or through a T5 regulation loop at intermediate power settings,
• establishing acceleration and deceleration fuel flowrates or schedules,
• N1 limitation to 100% stabilized with compensation (LP fan/compressor power setting),
• limitation of transient N1 overspeed during slam acceleration,
• protection against compressor surge,
• protection against N1 or N2 overspeed,
• protection against overheating (maximum permissible T5 temperature),
• monitoring of peripherals and computer internal circuits,
• power increase at take-off (at high altitudes or in warm weather conditions).
(1)
General operating principle
The computer determines the N2 power setting to be held for a given power lever position, from idle to full power, and for given Pt2/Tt2 conditions.
(2)
Power lever set to “full power” position
Regulation calculations are made directly in terms of N2 speed. The computer is programmed for maximum N2 as a function of T2 temperature. This basically corresponds to operation at a constant maximum T5 turbine temperature, producing an increasing thrust when the T2 temperature decreases.
Below a “flat-rating” T2 temperature (as a function of P2 pressure), a second N2 program limits the thrust to a constant value.
N2 is only held at the value computed by one of these two programs if the engine is not limited by the maximum N1 speed circuit (100% – with compensation) or the maximum T5 turbine temperature circuit (952°C (1745°F) or 978°C (1792°F) after SB F900-100 ).
(3)
Power lever set to “idle” position
Regulation calculations are made directly in terms of N2 speed. The computer is programmed for N2 power setting as a function of P2 pressure to produce the idle setting necessary to comply with the requirements of 5-second acceleration test bench performance. This program is used during flight. It corresponds to 350 lb test bench thrust.
A second program produces a reduced idle setting, corresponding to 220 lb test bench thrust. This program is used on the ground. Acceleration time from this idle setting is longer by about 1.8 seconds.
The computer automatically selects either idle setting as a function of a ground/flight signal. The ground signal is obtained only when the two main landing gear shock absorbers are compressed.
The power lever has a positive idle stop.
(4)
Power lever set to a position between idle and full power
Reduction of the power lever angle from full power produces a reduced power setting by comparing two calculation channels:
• N2 reduction in relation to full power N2 by means of a differential N2 correction program as a function of the power lever angle,
• T5 reduction in relation to full power T5 by means of a differential T5 correction program as a function of the power lever angle.
For cruise and climb power settings, the T5 loop has priority.
This makes climb possible with constant power lever position and constant T5.
Should the T5 signal fail or there be a short-circuit, the T5 loop is broken and regulation remains in terms of N2.
For power settings lower than cruise, regulation is by the N2 channel.
(5)
Starting
During the starting sequence, the fuel schedule is programmed at a constant fuel ratio of 6, up to a corrected N2 of about 20%, then increases with N2.
In the initial phase, the fuel schedule is increased by a fuel ratio of 5 by an enrichment system, which is automatically inhibited as soon as T5 temperature exceeds 400°F (204°C).
A T5 loop monitors the turbine temperature and reduces the fuel schedule if T5 reaches a maximum of 1350°F (732°C). This loop becomes inoperative as soon as the idle setting is reached.
The computer has an integral circuit enabling automatic interruption of the starting sequence at N2 = 50%.
(6)
Acceleration
Fuel flow during acceleration above the idle power setting is limited so as to avoid excessive T5 temperature. The corresponding program is a function of T2 temperature and N1 speed.
The fuel flow can also be limited by the surge protection system. This system includes a maximum fuel flow program as a function of N1 and N2 speeds with reduction factors for increased altitude or for acceleration following a deceleration.
(7)
Deceleration
The fuel flow reduction corresponding to the power lever position can be limited by the circuit which computes the minimum required flow.
At low power settings, this circuit determines the fuel flow required to avoid lean blow-out as a function of T2 temperature and N2 speed.
Moreover, it also determines a minimum fuel flow as a function of N1 speed and the position of the surge bleed valve.
These two flow calculations are compared with the minimum required fuel flow: the greatest of the three values is selected as the minimum required fuel flow.
(8)
Normal mode protections
(a)
Surge protection
Refer to the above paragraphs (Acceleration – Deceleration).
(b)
Overspeed
N2 regulation limits the HP spool power setting to 100% stabilized or 100.8% after SB F900-100 , although a transient setting of 103% is possible.
The N1 limiter keeps the LP spool power setting at 100% – maximum stabilized compensation, with the possibility of transient settings of 103%.
The overspeed governor (hydromechanical element) prevents the HP spool power setting from exceeding 104% by commanding modification of the fuel flow regulator valve position in response to P3 pressure received.
A computer circuit controlling the overspeed safety fuel shut-off valve can completely cut off fuel supply should the LP spool power setting reach 107% or the HP spool 109%. The control circuit has two branches, one digital, the other analog: any discrepancy between the two prevents action being taken against overspeed.
(c)
Overheating
Maximum T5 temperature limiter (952°C or 978°C (1745°F or 1792°F) after SB F900-100 ) and fuel flow limiter during acceleration (refer to above paragraphs). This limit is extended to 974°C or 996°C (1785°F or 1825°F) after SB F900-100 during a take-off with power increase.
(d)
Internal pressure
The hydromechanical fuel control unit P3 pressure limiter (limiting HP compressor discharge pressure) prevents excess pressure in the combustor by commanding P3 pressure leakage, thereby causing modification of the flow regulator valve position.
(9)
Monitoring
(a)
General
The digital electronic computer incorporates a number of circuits monitoring the principal internal and peripheral functions: these circuits make up the “BITE” (Built-in Test Equipment).
The occurrence of a failure causes a switch to the manual mode of regulation and illumination of the “CMPTR” light in the cockpit.
The computer memorizes transient failures for post-flight analysis if required.
(b)
Monitored circuits
Peripheral circuits
CODE ON COMPUTER FRONT PANEL

CIRCUIT

01

Tt2 sensor

02

Surge bleed valve solenoid A

03

Surge bleed valve solenoid B

04

Torque motor

05

Power lever potentiometer

06

T5 wiring harness

07

Manual mode selector solenoid

08

Overspeed safety valve solenoid

09

N1 monopole

10

N2 monopole

(c)
Internal circuits
Computer internal failures are indicated by code 11.
Settings outside maximum tolerances are indicated by code 12.
B.
Normal engine operation (N1 control) with SB F900-320-R1
The computer performs the following functions:
• conversion of analog input signals into digital signals in order to calculate output parameters, then conversion of these parameters into analog signals corresponding to fuel schedule and the position of the surge bleed valve,
• during starting, regulation of fuel flow, limitation of T5 temperature and automatic starting sequence interruption,
• holding ground or flight idle, when the power lever is set to “idle”,
• limitation of maximum thrust, when the power lever is set to “full power” (in particular, regulation of the “flat rated” thrust according to Pt2/Tt2 conditions),
• N1 power setting regulation, either directly at take-off or idle, or through a T5 regulation loop at intermediate power settings,
• establishing acceleration and deceleration fuel flowrates or schedules,
• N1 limitation to 100% stabilized with compensation (LP fan/compressor power setting),
• limitation of transient N1 overspeed during slam acceleration,
• protection against compressor surge,
• protection against N1 or N2 overspeed,
• protection against overheating (maximum permissible T5 temperature),
• monitoring of peripherals and computer internal circuits,
• power increase at take-off (at high altitudes or in warm weather conditions).
(1)
General operating principle
The computer determines the N1 power setting to be held for a given power lever position, from idle to full power, and for given Pt2/Tt2 conditions.
(2)
Power lever set to “full power” position
Regulation calculations are made directly in terms of N1 speed. The computer is programmed for maximum N1 as a function of T2 temperature. This basically corresponds to operation at a constant maximum T5 turbine temperature, producing an increasing thrust when the T2 temperature decreases.
Below a “flat-rating” T2 temperature (as a function of P2 pressure), a second N1 program limits the thrust to a constant value.
N1 is only held at the value computed by one of these two programs if the engine is not limited by the maximum N1 speed circuit (100% – with compensation) or the maximum T5 turbine temperature circuit (952°C (1745°F) or 978°C (1792°F) after SB F900-100 ).
(3)
Power lever set to “idle” position
Regulation calculations are made directly in terms of N1 speed. The computer is programmed for N1 power setting as a function of P2 pressure to produce the idle setting necessary to comply with the requirements of 5-second acceleration test bench performance. This program is used during flight. It corresponds to 350 lb test bench thrust.
A second program produces a reduced idle setting, corresponding to 220 lb test bench thrust. This program is used on the ground. Acceleration time from this idle setting is longer by about 1.8 seconds.
The computer automatically selects either idle setting as a function of a ground/flight signal. The ground signal is obtained only when the two main landing gear shock absorbers are compressed.
The power lever has a positive idle stop.
(4)
Power lever set to a position between idle and full power
Reduction of the power lever angle from full power produces a reduced power setting by comparing two calculation channels:
• N1 reduction in relation to full power N1 by means of a differential N1 correction program as a function of the power lever angle,
• T5 reduction in relation to full power T5 by means of a differential T5 correction program as a function of the power lever angle.
For cruise and climb power settings, the T5 loop has priority.
This makes climb possible with constant power lever position and constant T5.
Should the T5 signal fail or there be a short-circuit, the T5 loop is broken and regulation remains in terms of N1.
For power settings lower than cruise, regulation is by the N2 channel.
(5)
Starting
During the starting sequence, the fuel schedule is programmed at a constant fuel ratio of 6, up to a corrected N2 of about 20%, then increases with N2.
In the initial phase, the fuel schedule is increased by a fuel ratio of 5 by an enrichment system, which is automatically inhibited as soon as T5 temperature exceeds 400°F (204°C).
A T5 loop monitors the turbine temperature and reduces the fuel schedule if T5 reaches a maximum of 1350°F (732°C). This loop becomes inoperative as soon as the idle setting is reached.
The computer has an integral circuit enabling automatic interruption of the starting sequence at N2 = 50%.
(6)
Acceleration
Fuel flow during acceleration above the idle power setting is limited so as to avoid excessive T5 temperature. The corresponding program is a function of T2 temperature and N1 speed.
The fuel flow can also be limited by the surge protection system. This system includes a maximum fuel flow program as a function of N1 and N2 speeds with reduction factors for increased altitude or for acceleration following a deceleration.
(7)
Deceleration
The fuel flow reduction corresponding to the power lever position can be limited by the circuit which computes the minimum required flow.
At low power settings, this circuit determines the fuel flow required to avoid lean blow-out as a function of T2 temperature and N1 speed.
Moreover, it also determines a minimum fuel flow as a function of N1 speed and the position of the surge bleed valve.
These two flow calculations are compared with the minimum required fuel flow: the greatest of the three values is selected as the minimum required fuel flow.
(8)
Normal mode protections
(a)
Surge protection
Refer to the above paragraphs (Acceleration – Deceleration).
(b)
Overspeed
N2 regulation limits the HP spool power setting to 100% stabilized or 100.8% after SB F900-100 , although a transient setting of 103% is possible.
The N1 limiter keeps the LP spool power setting at 100% – maximum stabilized compensation, with the possibility of transient settings of 103%.
The overspeed governor (hydromechanical element) prevents the HP spool power setting from exceeding 104% by commanding modification of the fuel flow regulator valve position in response to P3 pressure received.
A computer circuit controlling the overspeed safety fuel shut-off valve can completely cut off fuel supply should the LP spool power setting reach 107% or the HP spool 109%. The control circuit has two branches, one digital, the other analog: any discrepancy between the two prevents action being taken against overspeed.
(c)
Overheating
Maximum T5 temperature limiter (952°C or 978°C (1745°F or 1792°F) after SB F900-100 ) and fuel flow limiter during acceleration (refer to above paragraphs). This limit is extended to 974°C or 996°C (1785°F or 1825°F) after SB F900-100 during a take-off with power increase.
(d)
Internal pressure
The hydromechanical fuel control unit P3 pressure limiter (limiting HP compressor discharge pressure) prevents excess pressure in the combustor by commanding P3 pressure leakage, thereby causing modification of the flow regulator valve position.
(9)
Monitoring
The N1 DEEC continuously monitors the necessary parameters and events, and periodically stores them in data buffers located within the N1 DEEC. These data buffers are then down-loaded through the ECTM system for evaluation of engine usage, updating of the engine log-book, and determination of required maintenance actions.
C.
Manual mode operation
(1)
General operating principle
Should the following failures occur:
• computer failure,
• computer power supply failure (voltage dropped below the 12.5 ± 0.5 V alert threshold, and not returned to the 15 ± 0.5 V nominal threshold),
the computer is automatically cut off and the “CMPTR” light illuminates on warning panel (2WW).
When the “CMPTR” light comes on, the computer control switch must be set to “MAN”. This maintains energization of the N1 and N2 overspeed safety circuit, which therefore remains operational as long as the failure is not a power supply failure, an N1 or N2 or overspeed circuit failure.
Should the regulation system function abnormally without the “CMPTR” light coming on, the pilot can also set the switch to “MAN” with the same result as in the previous case. If the switch were set to “OFF”, the overspeed safety circuit would be cut off.
In both cases, manual mode is adopted by closing of a fuel control unit electric valve (normally excited open by the computer). By means of a cam, the power lever drives a variable stop which shifts the overspeed governor threshold (set at 104% N2 in normal mode) and which, in manual mode, will limit N2 to lower values, in accordance with the power lever position.
The engine can be started in manual mode. Since T5 monitoring is no longer provided by the computer, the pilot must pay particular attention to this parameter. Fuel flow during starting in manual mode is greater than during normal starting. Moreover, there is no automatic starting sequence interruption at 50%. The pilot must manually interrupt the sequence by use of the “START STOP” switch located on the overhead panel.
(2)
Protections
Anti-surge: in the event of computer failure, the surge bleed valve adopts the “1/3 open” position. Sharp movements of the power lever should be avoided since the valve cannot open completely.
Maximum fuel flow during acceleration is also less in manual mode, which reduces the risk of surges.
Loss of T5 temperature monitoring: the pilot must pay attention to the T5 temperature indication, particularly in hot weather at high power settings.
Overspeed: as mentioned above, overspeed protection is generally maintained for N1 and N2 (107% and 109%) by setting the computer switch to “MAN”. At the same time, N2 is manually limited by the hydromechanical fuel control unit.
P3 pressure limiter: remains operative.
(3)
Aircraft performance
In manual mode, take-off thrust can be reduced by 20% (in hot weather).
Specific fuel consumption increases (by approximately 3% in average conditions) as a result of surge bleed valve opening.
Idle thrust is generally greater than thrust in normal “AUTO” mode (to be borne in mind when landing).

Figure 1: FUEL REGULATION SYSTEM – NORMAL MODE

Figure 2: SURGE CONTROL – LOCATION OF COMPONENTS – OPERATION

Figure 3: ENGINE COMPUTER – PRINCIPLE DIAGRAM

Figure 4: ENGINE COMPUTER CONTROLS AND INDICATIONS

Figure 5: WIRING DIAGRAM (A/C < 179)

Figure 6: N2 DEEC

Figure 7: N1 DEEC