Page
GENERAL ..................................................................................................... 7-3
SYSTEM LOGIC......................................................................................... 7-3
CONTROLS and ANNUNCIATIONS .......................................................... 7-3
OPERATION ................................................................................................. 7-4
STALL WARNING SYSTEM....................................................................... 7-4
STALL IDENTIFICATION SYSTEM ........................................................... 7-4
Figure 1 - Stall Valve Annunciators ........................................................ 7-4
Figure 2 - Variation of Stall Identification Angle With
Rate of Increase of Vane Angle ............................................. 7-5
THIRD STALL IDENTIFICATION CHANNEL ............................................. 7-6
Figure 3 - Stall Warning and Identification.............................................. 7-6
Figure 4 - Stall System Pitot Static Block Diagram................................. 7-7
SYSTEM FAULTS and ANNUNCIATIONS .................................................. 7-8
Figure 5 - System Fault Annunciators .................................................... 7-8
FLAP ASYMMETRY ................................................................................... 7-9
WEIGHT-ON-WHEELS ASYMMETRY....................................................... 7-9
SSU SELF TEST ........................................................................................ 7-9
SYSTEM ANNUNCIATORS........................................................................ 7-10
Table 1: Summary of Annunciators ...................................................... 7-10
SYSTEM POWER SUPPLIES..................................................................... 7-10
Table 2: Power Supplies....................................................................... 7-10
STALL WARNING and IDENTIFICATION LOGIC ..................................... 7-11
Figure 6 - Stall System Flow Logic ....................................................... 7-11
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STALL WARNING/IDENTIFICATION
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Hawker 800XP Pro Line 21
Section III - SYSTEMS DESCRIPTION
NOTE: This section applies to 800XP Pro Line 21 airplanes prior to Serial No. 258675.
For airplanes Serial Nos. 258675 and subsequent, refer to Section VIII SUPPLEMENTS for
Supplement P/N 140-590032-0041.
A stall warning and identification system is provided to emphasize the airplane’s natural cues available at the point of stall.
The system functions are
• Stick shaker (warning)
• Stick pusher (identification)
The system consists of
• Two sensing channels, each utilizing an airflow angle sensor vane.
• Two Signal Summing Units (SSUs).
• Two stick shaker motors.
• A hydraulic operated actuator with two electro-hydraulic valves.
• A third sensing channel, which utilizes pitot pressure from the right pitot head, static pressure from the forward static plates and stall vent pressure from the left and right stall vents.
• A stall identification sensor.
• Annunciators and test switches.
SYSTEM LOGIC
1. It is impossible for a stick push to occur before a stall warning (stick shake).
2. No single active fault of an SSU or relay can cause the operation of a stall valve or the associated red STALL VALVE annunciator.
3. The autopilot is disengaged when a stall warning signal is initiated. This prevents the autopilot from attempting to counteract the resulting stick shake operation or a subsequent stick push.
CONTROLS and ANNUNCIATIONS
System faults are indicated on two groups of amber annunciators, one per pilot.
Three STALL switches are located in the TEST section of the overhead roof panel. Anti-icing heating of the airflow sensor vanes is controlled from the PITOT/VANE HEAT switches.
Indication of failure of the vane heaters is provided by the two amber L and R VANE HTR FAIL annunciators also located on the overhead roof panel and by the ICE PROT repeat annunciator on the
MWS panel.
There are no control switches, the stall warning part of the system becomes armed on takeoff
(no weight-on-wheels), while the stall identification part of the system becomes armed 6 seconds after takeoff.
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Section III - SYSTEMS DESCRIPTION
STALL WARNING SYSTEM
The stall warning system uses an electrically driven stick shaker on each control column to provide a physical warning of an approaching stall to the pilots.
Angle of attack is derived from two electrically heated airflow angle sensor vanes mounted one on each side of the forward fuselage. Electrical signals proportional to vane angle are sensed in the associated
Signal Sensor Unit which also receives inputs relating to flap angle. From the flap angle signal, the SSU calculates the point of stall warning. When the vane angle corresponds to that point the SSU provides an output to operate the stick shaker motor on each control column.
The stall warning system is inhibited while the airplane is on the ground with weight-on-wheels to prevent wind gusts triggering false stick shaker operations. At takeoff, the system is armed and begins monitoring the pitch attitude of the airplane.
STALL IDENTIFICATION SYSTEM
The stall identification system uses a hydraulic stick pusher to force the control column forward (pitch down) at the calculated point of stall. The stick pusher is powered by main hydraulic system pressure
(backed by the main accumulator), the rate of operation being controlled by a fluid restrictor.
Control of the hydraulic pressure to the stick pusher is via two independent stall valves (A and B), connected in series and mounted integral with the stick pusher. Both stall valves must be open to activate the unit.
M6950_0
HA00C
017045AA.AI
Figure 1
Stall Valve Annunciators
The output from one SSU energizes one stall valve, and an associated red STALL VLV (A or B) OPEN annunciator is illuminated to indicate that the valve is being signalled to open (reference Figure 1).
The SSU uses the vane sensor and flap angle inputs to calculate the point of stall. The rate of increase of vane angle may also modify the calculation, i.e. the point of stall being advanced when the rate of increase is high dynamic stall (reference Figure 2).
When the vane angle agrees with the calculated point of stall, the SSU produces an output
(stall identification) to energize the associated stall valve and annunciator.
When a SSU produces a stall warning output, which is then followed by an identification signal, the warning signal latches the stall identification relay for the same channel (reference Figure 3). A warning signal from either channel will disconnect the autopilot and operate the stick shaker. The latch is removed when the warning output ceases. This makes sure the stick push is maintained until the airplane has reached a nose-down attitude well below the stall point.
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Section III - SYSTEMS DESCRIPTION
28
26
FLAP 0
°
IDENT
FLAP > 0
°
IDENT
24
22
FLAP 0
°
WARN
FLAP 15/25
°
WARN
20
FLAP 45
°
WARN
18
16
14
0 1 2 3 4 5 6
VANE RATE - DEGREES/SECOND
7 9
NOTE: HFD is the Horizontal Fuselage Datum.
Figure 2
Variation of Stall Identification Angle with Rate of Increase of Vane Angle
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Section III - SYSTEMS DESCRIPTION
THIRD STALL IDENTIFICATION CHANNEL
A third channel for stall identification is provided by a pitot/static system which uses pitot pressure (P2) from the right pitot head, static pressure (S6) from the forward static vents and a vent pressure (V) from left and right stall vents. The stall vents are located on the under-side of the left and right wings
(reference Figure 4).
These pressures are sensed by a capsule operated stall detector, which is set to produce an output at a point between the settings for the stall warning and identification signals from the SSUs.
The output from the third channel sensor energizes a relay which connects the stall identification output from one channel’s SSU to the stall valve of the other channel. Thus, with the third channel output activated, both stall valves A and B will open following a stall identification output from only one SSU, thereby ensuring system integrity should a SSU fail.
VANE
ANGLE
SENSOR
I
N
P
U
T
SSU
WARN
IDENT
FLAP
ANGLE
VANE
ANGLE
SENSOR
I
N
P
U
T
IDENT
WARN
SSU
3rd CHANNEL
STALL VENT
LEFT and
RIGHT
STICK -
SHAKER
MOTORS
3rd CHANNEL
STALL VENT
PITOT
PRESSURE
3rd
CHANNEL
STATIC
PRESSURE
HYDRAULIC
PRESSURE
STALL
VALVE A
STALL
VALVE B
STICK PUSHER
Page 7-6
Figure 3
Stall Warning and Identification
Sub-section 7
STALL WARNING/IDENTIFICATION
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Hawker 800XP Pro Line 21
Section III - SYSTEMS DESCRIPTION
Left
Stall
Vent
V1
Left Forward
Static Vent Plate
6
Stall Ident
(Autopilot Disconnected)
V
Stall
Detector P
S
Pitot
Isolation
Valve
V
Stall
Detector P
Stall Ident
3rd Channel
S
P2
S6
S6
Right Forward
Static Vent Plate
6
Right
Pitot
Head
P2
Right
Stall
Vent
V2
LEGEND
= Pitot Pressure
= Static Pressure
= Stall Vent Pressure
= Pitot Drain
= Static Drain
= Stall Vent Drain
Pilot’s Operating Manual
Revision A2: Nov, 2004
Figure 4
Stall System Pitot Static Block Diagram
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STALL WARNING/IDENTIFICATION
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Hawker 800XP Pro Line 21
Section III - SYSTEMS DESCRIPTION
SYSTEM FAULTS and ANNUNCIATIONS
The duplication of the stall warning system makes sure a single passive fault cannot prevent a stick shake occurring. Should an active fault develop, the faulty system can be isolated via the appropriate circuit breaker.
The remaining good system will still operate both stick shaker motors. The stall identification system is designed that a single active fault cannot give an inadvertent stick push, while making sure a single passive fault would not prevent a push operation occurring, when required.
All annunciator warnings in the stall warning and identification system will also cause a repeater STALL
IDENT annunciator on the MWS panel to illuminate (reference Figure 5). The power to energize a stall valve is routed via the identification relay of one channel and the warning relay of the other channel.
A monitoring circuit will cause an IDENT 1 or IDENT 2 annunciator (depending on the channel at fault) to be illuminated after a 4 second time delay, if an identification signal from one SSU has been triggered without a warning signal from the other SSU.
The IDENT 1 or IDENT 2 annunciators are part of the IDENT/INHIB switches provided for both pilots.
When an IDENT annunciator illuminates, either pilot can push the associated switch to inhibit the faulty channel. The INHIB annunciator part of the switch will then illuminate. The third channel sensor, together with the remaining SSU would provide a stick push operation when required.
MWS Panel
M6949_0
HA00C
017044AA.AI
Figure 5
System Fault Annunciators
The pilots may attempt to reset the failed channel by operating an INHIBIT RESET switch located on the stall diagnostic panel (forward side of the Pilot’s bulkhead).
Should the channel fail again after reset, it should be inhibited and left in that condition for the remainder of the flight.
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Section III - SYSTEMS DESCRIPTION
FLAP ASYMMETRY
If asymmetry between the left and right flap positions exists for more than 2 seconds, then the FLAP annunciator (Pilot’s group only) will illuminate.
WEIGHT-ON-WHEELS ASYMMETRY
If asymmetry between the positions of the left and right weight-on-wheels relays exists for more than 4 seconds, then a SQUAT annunciator (Copilot’s group only) will illuminate.
SSU SELF TEST
A built-in test within the SSU detects the following faults:
• Loss of 26 VDC supply
• Loss of internal power or short circuit
• Loss of airflow angle sensor excitation
• Loss of flap position input
• Airflow angle sensor transformer winding open or short circuit
If any of the above occur, an external relay causes a SSU annunciator to illuminate. If the weight-on- wheels switch is in the flight condition, a magnetic indicator associated with the faulty SSU will display white. The magnetic indicators are located on the stall identification diagnostic panel.
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Section III - SYSTEMS DESCRIPTION
Table 1: Summary of Annunciators
Function Annunciator
Airflow angle sensor left or right vane heating malfunction
VANE HTR FAIL
L (R)
# VANE
HTR FAIL
Flap position asymmetry FLAP
FLAP
Stall identification
channel 1 (2) (3) fault
IDENT 1 (2) (3)
IDENT #
Signal Summing Unit fault SSU SSU
Weight-On-Wheels asymmetry
SQUAT
SQUAT
MWS Panel
ICE
PROT
STALL
IDENT
Stall valve A (B) operating
STALL VLV
A (B) OPEN
STALL
VLV #
OPEN
Table 2: Power Supplies
Panel Location
Row/Column
DA-D
B/1
DA-D
B/4
DA-D
B/6
DA-D
B/2
DA-D
B/5
DA-D
B/7
DA-D
B/3
Circuit Breaker Circuit or Equipment
STALL IDENT 1 26 VAC input to SSU 1
STALL VLV A
STALL WARN
MOTOR 1 (LH)
28 VDC to stall valve 1 and annunciators
28 VDC to stick shaker motor 1
STALL IDENT 2 26 VAC input to SSU 2
STALL VLV B
STALL WARN
MOTOR 2 (RH)
28 VDC to stall valve 2 and annunciators
28 VDC to stick shaker motor 2
STALL IDENT 3 28 VDC to SSU 3
Page 7-10 Sub-section 7
STALL WARNING/IDENTIFICATION
Busbar
XS 1
PS1(a)
PS1(a)
XS 2
PS2(a)
PS2(a)
PE
Pilot’s Operating Manual
Revision A2: Nov, 2004

ANGLE OF ATTACK MONITORED BY
AIRFLOW ANGLE SENSOR
STALL WARNING TRIGGER POINT &
STALL IDENTIFICATION TRIGGER
POINT MODIFIED BY FLAP ANGLE
ANGLE
OF ATTACK
INCREASING?
NO
YES
Channel 1
SSU 1 CALCULATES APPROACHING
STALL AND INITIATES A WARNING
SIGNAL
WARNING SIGNAL FROM EITHER CHANNEL
DISCONNECTS AUTOPILOT AND OPERATES
THE STICK SHAKER
Channel 2
SSU 2 CALCULATES APPROACHING
STALL AND INITIATES A WARNING
SIGNAL
ANGLE
OF ATTACK
INCREASING?
YES
NO PREVENTIVE
ACTION TAKEN
BY PILOT
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Sub-section 7
STALL WARNING/IDENTIFICATION
ANGLE OF ATTACK
CONTINUES TO INCREASE
Hawker 800XP Pro Line 21
Section III - SYSTEMS DESCRIPTION
STALL IDENTIFICATION TRIGGER POINT
MODIFIED BY RATE OF INCREASE OF
ANGLE OF ATTACK. SSU 1 AND/OR
SSU 2 INITIATE IDENTIFICATION SIGNAL
WHEN THE AIRPLANE IS AT POINT OF STALL
Channel 3
APPROACHING STALL SENSED AT
UNDER-WING PRESSURE VENTS
3rd CHANNEL SENSOR IS ACTIVATED
BOTH SSU IDENT
SIGNALS OPERATED
ONLY ONE SSU
IDENT SIGNAL
OPERATED
3rd CHANNEL RELAY ENERGIZES
TO CONNECT ACTIVE SSU OUTPUT
TO BOTH STALL VALVES
NEAR
TO STALL?
YES
NO
OR
STALL VALVE A
OPEN
AND
STALL VALVE B
OPEN
STICK PUSHER ACTIVATED
Figure 6
Stall System Flow Logic
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