37 Questions
What is the purpose of the Stab Primary Trim Fail CAS message?
To alert the crew that the HSTS is in Backup mode.
In what scenario does the HSTS enter Backup mode?
When both FCCs are not available on power up.
How does the HSTS transition from Normal mode to Backup mode?
When no valid input is received from either FCC for more than one second.
What triggers the HSTS to transition from Backup mode to Normal mode?
When either FCC provides three consecutive frames of valid data.
When does the HSTS operate in Maintenance mode?
When all interlocks are valid.
What are the components of the HSTS system?
Horizontal Stabilizer Control Unit (HSCU)
How many control channels does the HSCU have?
Two
How does the HSCU operate in terms of configuration?
Active/Standby
What are the two states of the HA (Hydraulically Active) system?
The two states of the HA system are Hydraulically Active and Damped Bypass.
What is required for the HA system to be in the Hydraulically Active state?
For the HA system to be in the Hydraulically Active state, hydraulic pressure must be available and the actuator REU must electrically hold a solenoid.
What is the purpose of the Damped Bypass state in the HA system?
The purpose of the Damped Bypass state in the HA system is to resist movement of the control surface proportional to the rate at which it is moved, in order to prevent control surface flutter in flight and provide gust protection during ground operation.
How can pilots experience the behavior of the Damped Bypass actuators?
Pilots can directly experience the behavior of damped bypass actuators by rotating an aileron surface upward or downward with the palms of their hands during preflight when hydraulic pressure is not available to either the left or right system.
What are the three modes of operation for the EBHA (Electrical Backup Hydraulic Actuator) system?
The three modes of operation for the EBHA system are Hydraulically Active, Electric Backup, and Damped Bypass.
How does the EBHA system function during normal hydraulic operation?
During normal hydraulic operation, the EBHA has the same inputs and functions as the HA (Hydraulically Active) system.
What happens if a surface cannot be powered by an engine-driven hydraulic source in the EBHA system?
If a surface cannot be powered by an engine-driven hydraulic source, an Electrical Backup (EB) hydraulic pump will provide the EBHA actuator with hydraulic pressure to operate the flight control surface.
What is the purpose of the Damped Bypass mode in the EBHA system?
The purpose of the Damped Bypass mode in the EBHA system is to resist movement of the control surface proportional to the rate at which it is moved, in order to prevent control surface flutter in flight and provide gust protection during ground operation, similar to the Damped Bypass state in the HA system.
What happens if either FECU channel fails?
The FECU loses the ability to control the flaps, but a remaining healthy channel continues to report flap positions and flap status.
How do the flaps behave in the event of a total loss of hydraulic or electrical power to the flap system?
The flaps will remain in their last position when power was lost.
How does the FCC angle-of-attack limiting schedule behave when the aircraft is 'on ground stationary'?
Defaults to the 'clean and protected leading edges' condition for all flaps settings and remains latched in this condition up to 1500 ft radar altitude.
What does the FECU do in the event of an uncommanded flap motion?
The FECU will immediately detect the failure and arrest the uncommanded motion by de-energizing the HCM SOV.
How does the FECU interface with other systems?
The FECU interfaces with FCC and avionics systems through digital Buses.
What information does the FECU provide to the CMC?
The FECU provides the CMC with flap system fault reporting / isolation.
What is the role of the FECU in providing information to the avionics CAS?
The FECU provides the avionics CAS with flap system failure annunciation and flap surface position data / indication.
Why was the logic implemented where the FCC angle-of-attack limiting schedule defaults to the 'clean and protected leading edges' condition when 'on ground stationary'?
To support the immediate return scenario where flaps cannot be extended from 0°.
What is the purpose of adding the radar altimeter logic?
To reduce the chances of automatic deployment when the throttle is brought back to idle.
What happens if both radar altimeters are invalid during landing?
They are removed from the logic, leaving only the wheelspeed and flap position for deployment.
When landing with flaps less than 22 degrees, what action enables the spoilers to deploy?
Depressing the GPWS GND SPLR / FLAP ORIDE switch to ON.
Where can a full description of the Primary Flight Display be found?
Section 2B-05-00.
Which section of the manual includes a description of the Flight Controls 2/3 synoptic page?
Section 2B-07-00.
What mode do the outboard spoiler EBHAs operate in if the right hydraulic system is lost?
Electric Backup (EB)
Are speed brake and ground spoiler functions available when the Primary Flight Control System (PFCS) is in Backup mode?
No
What components control ground spoiler deployment and speed brakes?
The Flight Control Computers (FCCs)
How do the FCCs send the spoiler position commands?
Via two digital databuses to each of the REUs
How is the speed brake function performed?
By manually commanding the speed brake lever
What components provide the speed brake handle input to the FCCs?
Four Rotary Variable Differential Transducers (RVDTs)
What do the control laws resident within the FCCs provide for the deployment of speed brakes?
The necessary interlocks and protection
How is ground spoiler deployment controlled?
Automatically controlled by the FCCs
Study Notes
Horizontal Stabilizer Trim System (HSTS) Modes
- HSTS has three modes: Normal, Backup, and Maintenance
- Backup mode: HSTS enters Backup mode if both FCCs are not available on power up or when no valid input is received from either FCC for more than one second
HSTS Components
- Horizontal Stabilizer Control Unit (HSCU): a dual-channel controller that interfaces with the primary flight controls system through the FCCs
- HSCU interfaces with CAS and CMC systems through the aircraft MAUs, as well as the flight deck via the BACKUP PITCH switch on the center console
- The HSCU has two mechanically and electrically separate control channels, each using a hardware and software dissimilar command/monitor architecture
Speed Brake and Ground Spoiler Functions
- Ground spoilers and speed brake functions are not available when the Primary Flight Control System (PFCS) is in Backup mode
- Ground spoilers and Speed Brake auto-retract are not available in Direct Mode
- The FCCs control ground spoiler deployment and speed brakes based on pilot wheel positions and speed brake lever
- The FCCs perform necessary control law computations and send commands via two digital databuses to each of the REUs
Horizontal Actuator (HA) States
- Hydraulically Active: HA in normal operation, with pressurized fluid from the aircraft hydraulic system
- Damped Bypass: HA in a passive condition, resisting movement proportional to the rate at which the surface is moved by either airflow or the other actuator
Electrical Backup Hydraulic Actuator (EBHA)
- Has three modes of operation: Hydraulically Active, Electric Backup, and Damped Bypass
- In the event of a surface not being powered by an engine-driven hydraulic source, the Electrical Backup (EB) hydraulic pump provides hydraulic pressure to operate the flight control surface
Flap System
- Flap and Slats Control Unit (FECU) provides the CMC with flap system fault reporting and isolation, and the avionics CAS with flap system failure annunciation and flap surface position data/indication
- The FCC angle-of-attack limiting schedule defaults to the 'clean and protected leading edges' condition for all flaps settings when 'on ground stationary' and remains latched in this condition up to 1500 ft radar altitude
Test your knowledge on the operations of an aircraft's Flight Control System, including alerts, modes, and inputs. Learn about the conditions that lead to the HSTS entering Backup or Normal mode based on FCC availability and input validity.
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