Overview
The power control system is that system which controls the forward and reverse thrust of the engines.
The power control system controls the engine speeds from maximum reverse thrust to maximum thrust, as set on the throttle lever assembly in the flight compartment. Power control of the engines is automatic (auto throttle system) or manual.
Each throttle lever moves a dual-channel rotary-variable differential-transformer (RVDT) and each of these connects to a specified EEC channel. Reverse thrust is set manually only (with the reverse thrust lever).
05/31/16
Throttle Quadrant
The throttle quadrant has the components that follow:
- Two throttle levers (one for each engine)
- Two reverse thrust levers
- Two auto throttle on/off switches
- Two fuel cutoff switch/lights
- Two rotary variable-differential transformers (RVDT) (with two channels)
- Four electrical receptacles
Mounted on the center pedestal in the cockpit is the throttle quadrant assembly (TQA), consisting of dual throttle levers. The levers are used to control the engine power settings.
Throttle position information is transmitted by four rotary variable differential transformers (RVDTs) connected to each throttle lever. Two RVDTs are connected to the flight control unit (FCU) and two RVDTs are connected to the electronic engine controller (EEC). An engine run switch and a "finger lift" lever (thrust reverser operation) for each engine are also located on the TQA.
The EEC provides an excitation current to the throttle resolvers. The resolvers generate a voltage relative to throttle position which the EEC then reads as a power demand signal and sets engine power accordingly.
The resolvers are hardwired to the EEC. There is no mechanical link between the flight deck levers and the engines (fly-by-wire system).
The TQA has autothrottle servo drive motors. These power drives, one for each throttle lever, move the levers during the autothrottle mode as commanded by the IAC. The drive motors are connected to the throttle levers such that a motor jam or failure can be overridden by the pilot.
Described below are all the throttle functions and controls.
Throttle Settings
Forward thrust is set by positioning the main throttle levers (manually or automatically) between idle and maximum. Within this power range (which is not necessarily full throttle range) there are various power levels such as:
| Maximum Takeoff | MTO |
|---|---|
| Maximum Continuous | MCT |
| Maximum Climb | MCL |
| Flexible Takeoff | Flex TO |
| Flexible Climb | Flex CL |
Reverse thrust is by manual selection only and is controlled to a Reverse Throttle Lever Angle (RTLA) versus N1 relationship.
Throttle Lever/EEC Interface
In response to throttle lever settings, the EEC has two modes to set steady state power: Engine pressure ratio (EPR) and N1, and a modulated mode to govern idle RPM setting. N1 and idle control are detailed later in this section. The primary mode for setting steady state power above idle is EPR which is a ratio of pressures P50 to P20.
Although idle is controlled to an N2 RPM value by the EEC, an equivalent EPR is also calculated. This is done so that the EEC can establish the throttle resolver angle (TRA) versus EPR relationship throughout the operating range.
Throttle Rigging
If maintenance work on the throttle/RVDT assembly has been carried out or if the EEC is changed, it will be necessary to carry out a three point throttle rigging check. This will enable the EEC to compensate for mechanical tolerances in the setting up of the throttle quadrant.
The rigging check will be carried out during maintenance at the following three mechanical stops:
- Max Forward Position
- Forward Idle Position
- Reverse Idle Position
The EEC will read the throttle position (TRA) at these three points and generate an EPR versus TRA schedule such that rigging inaccuracies are compensated for.
Idle Control
The basic minimum idle is controlled to an N2 value as a function of temperature and altitude. However, the EEC will control idle power to prevent the engine operating below certain parameter minimum limits such as:
| P30 | to ensure that cabin bleed and anti-ice demands can be met |
|---|---|
| N1 | to prevent ice accumulation on the fan on the ground and in flight |
| N2 | to ensure that the Variable Frequency Generators stay on line |
| T30 | to protect against inclement weather by opening bleed valves to aid rejection of water and maintain the surge margin, commanding continuous ignition to maintain combustion, as well as increasing engine speed by an appropriate margin |
EEC initiated idle selections are as follows:
- High idle range (70 - 85% N2) is commanded when the TRA is in the forward idle position and the aircraft is in an approach configuration
- Discrete ARINC bit from IAC confirming approach configuration (gear down/ flaps > 25 degrees)
- Discrete ARINC bit from IAC confirming approach configuration (gear down/ flaps > 25 degrees)
- High idle range is maintained, if the EEC cannot determine whether or not an approach configuration has been set up
- Discrete ARINC bit from IAC confirming approach configuration, either not available or invalid
- Discrete ARINC bit from IAC confirming approach configuration, either not available or invalid
- High idle range is maintained for 5 seconds following touch down, then switched to Low idle (64 - 85% N2), unless T/R selected during this period at which point EEC commands Reverse idle
- Ensures engine will meet requirements for takeoff thrust in case of aborted landing
- Ensures engine will meet requirements for takeoff thrust in case of aborted landing
- Low idle range is commanded when the TRA is in the forward idle position and the aircraft is not in an approach configuration
Warning:
N1 operating limitation for the engine ground run, the N1 rpm operation limit is as follows:
- When the Aircraft is stable (The engine in forward thrust only), the stabilized engine operation in the speed band of 66 to 80% N1 (Fan speed) is not permitted.
Automated Keep Out Zone
A keep out zone (KOZ) is required on the BR700-710A2-20 to protect the engine from the possibility of inducing fan excitations which may be a contributing factor to fan disc cracking. To achieve this, a KOZ is required for ground running only (static case). The critical operating condition is when the engine speed has stabilized within the defined keep out zone and the aircraft is stationary in crosswind conditions. This KOZ logic will be provided in the EEC to prevent the engine stabilizing within the critical zone during static ground running.
Keep Out Zone Logic
The KOZ shall be armed when:
- Aircraft is on ground (WOW = true)
- CAS < 31 kt
- Parking brake on is true
If KOZ is armed and the engine is commanded to stabilize within the KOZ boundaries, then KOZ will activate and the EEC will command the engine to either the upper or lower KOZ boundary. While the KOZ is active, any change of thrust command within the KOZ range will not result in an engine response.
With KOZ is armed, activation of the KOZ logic depends only on N1 mechanical speed being stabilized within the KOZ boundaries. The relevant KOZ boundaries are 66.1% and 79.9% N1. When KOZ activates, the engine will be commanded to either the upper or lower boundary dependent on:
- Actual N1 speed above or below the midpoint (EPR control mode)
- N1 command above or below the midpoint (N1 control mode)
Engine control will be to an N1 command for KOZ active, regardless of whether the engine is in EPR or N1 control mode.
Takeoff Thrust
Rated Thrust
MTO is achieved by advancing the throttles manually or automatically to the forward hard stop position. The EEC includes limiter functions to prevent exceedances of N1, N2, P30, and Fuel Flow.
Lock-up Mode
During the Lockup Mode the Bleed debits are locked in and the EEC ignores changes to bleed debits to prevent any large or sudden changes in EPR during the critical flight phase of takeoff. This mode is automatically activated as the aircraft exceeds the maximum taxiing speed of 60 kts during takeoff. It is deactivated when any one of the following conditions is true:
- Throttle is manually moved back to the Idle position
- Altitude above runway exceeds 400 feet
- CAS exceeds 300 knots
- Mach number exceeds 0.55
Reduced Thrust Takeoff (FLEX)
The use of FLEX takeoff thrust is permissible when aircraft weight and runway conditions are such that full power is not necessary. The advantages of flex power are less wear and lower turbine operating temperatures which will prolong engine life and reduce maintenance costs.
Flex takeoff thrust is implemented by the use of an assumed temperature higher than ambient day temperature and is subject to certain certifying authority requirements such as:
- The use of flex thrust is always at pilot discretion
- When conducting a flex takeoff, max takeoff can be selected if required at any time, without introducing any control difficulties
- Reduced thrust does not result in loss of any function, engine failure warnings, or takeoff configuration warnings
- At least 75% of full rated thrust is used on all takeoffs
Reduced Power Climb
In the same way as utilizing derated takeoff thrust, reduced climb thrust can be used to operate the aircraft without incurring noise violations.
Note:
Both the reduced power takeoff and reduced climb power values will be calculated by the FMS.
EPR Ratings
Idle EPR Reference
The EPR command for engine control is calculated as a linear interpolation between the EPR idle reference at the forward idle TRA set point and the maximum available EPR at the maximum forward TRA set point. At steady state idle the engine will be controlled to a minimum limiter not EPR, and hence the EPR idle reference does not define idle power.
EPR Rating Values
EPR rating values shall be calculated for Maximum Takeoff (MTO), Maximum Continuous (MCT), Maximum Climb (MCL) and Maximum Cruise (MCR) determined as a function of flight phase condition (air data) and bleed status. An EPR idle reference shall be calculated as a function of ambient conditions.
Trim Functions
The data entry plug (DEP) is a hardwired pin programmable connector, attached to the EEC. The DEP contains EPR and ITT trim data necessary for the trim functions.
ITT Trim
ITT is a practical means of measuring the engine parameters that limit the amount of thrust that an engine can deliver. In order to ensure that all engines have the same ITT redline a trim will be applied to the measured ITT.
EPR Trim
EPR trimming is necessary to ensure that all engines of the same build standard have the same EPR to thrust relationship at pass-off testing and also that actual EPR from altitude test data is matched to calculated performance figures. The EEC reads the DEP trim data and applies the necessary actual filtering for the purpose of cockpit display stability.
Alternate Control Mode/N1 Reversion
The EEC may initiate a reversion to Alternate Control Mode in order to accommodate detected failures which prevent continued operation in primary EPR control mode. This is called a Soft reversion. Once initiated, a Soft reversion is latched and may only be reset when the fault causing the reversion is no longer present and the pilot Hard reverts the engine. A return to primary EPR control mode can then be achieved by toggling the appropriate engine selector switch on the Engine Control Panel on the center pedestal.
The EEC shall check for verification of the ratings structure. Ratings information is stored within the EEC in the form of look-up tables. The ratings structure shall be verified by a check between a ratings application code, programmed into the EEC, and a rating identifier code derived from the pin programmable DEP, connected to the EEC.
If there is a mismatch between the two codes, the control shall revert to Alternate Control Mode and the change will be indicated to the crew.
At the time a Soft reversion (reversion caused by anything other than Pilot action) is initiated, the EEC shall add a fixed bias to the N1 schedule in order to maintain the same N1 as at the time of reversion, thereby preventing a thrust bump. As the TRA is varied, the fixed bias will be continually applied to the N1 schedule until the Pilot selects a Hard reversion.
The pilot may initiate a Hard reversion to Alternate Control Mode. This command shall be input to the EEC via ARINC 429 bus. When the Pilot selects Alternate Control, no bias is applied to the N1, and the N1 is based on the TRA and the flight/ambient conditions prevalent at the time of selection. This pilot initiated selection may cause a thrust bump.
Note:
Soft reversion is software-controlled; Hard reversion is hardware-controlled (manual selection).
When a hard reversion is selected, the FADEC will reduce maximum thrust by 7% to attempt to not exceed the N1 of 99%.
Caution:
Before selecting alternate control mode switch to N1 position, slightly retard the power lever, as N1 bias will be removed and engine fuel flow will be higher for the throttle position (richer FF). If throttle was left at max forward power position, the N1 would over boost the engine, or on a hot day ITT limit would be exceeded.
Autothrottle System
The Autothrottle (AT) system provides full flight regime thrust management through automatic positioning of the throttle levers in the Throttle Quadrant Assembly (TQA). The TQA houses the power levers and an independent AT servo for each throttle lever. The control of engine thrust is achieved by modulation of the throttle lever. Movement of the lever is detected by a coupled dual Rotary Variable Differential Transformer (RVDT) producing electrical signals dependent upon the lever position. The RVDTs are housed inside the TQA.
The No. 1 and No. 2 IACs each house an AT computer. They are resident on the FMS processor card and operate through that processor. Each computer is completely independent from the other. There is no automatic transfer between AT functions. The TQA receives digital rate commands from the active AT and moves the throttles accordingly. Throttle rate is fed back to the AT digitally to close the loop. The active AT provides limited electronic engine trim commands directly to the FADEC for fine adjustment and engine sync.
Each throttle lever is driven by a smart power drive integral to the TQA, which is commanded by the AT via an ARINC 429 data bus. If necessary, the pilot can manually override the AT by direct operation of the throttle levers. The TQA also contains the AT engage/disengage switches, the AT Quick Disconnect buttons and the Takeoff Go-Around (TOGA) buttons.
The AT computer is part of the FMS in the Integrated Avionics Computer (IAC). It will calculate the required EPR command based on inputs from the aircraft and drive the throttle servo to the desired position relative to the two calculated values below:
- EPR max – The maximum EPR for the ambient conditions
- EPR idle – The value of EPR at idle for the ambient conditions
This in turn places a power demand on the EEC which will also compute an EPR command. The EEC EPR command is transmitted to the IAC for comparison with the AT EPR command, therefore providing closed loop control. Any trim value required to compensate for errors on the servo loop positioning system of the throttles will be calculated in the AT computer and transmitted to the EEC.
The AT system modulates thrust to provide both closed loop thrust control, as well as closed loop speed control, such that the AT operation is compatible with the AP/FD control at all times.
The autothrottle system performs the following functions:
- Operation over the full range of available forward thrust for two engine operation. The autothrottle will not operate under single engine conditions
- Hands-off operation from takeoff to landing
- Engine synchronization
- Electronic Thrust Trim System (ETTS)
The dual Electronic Thrust Trim System (ETTS) provides limited authority thrust trimming, over the full flight regime, via electronic trim commands to the FADEC.
The AT has two basic modes of operation:
- Thrust Control for the following AP/FD modes:
- T/O (Takeoff)
- GA (Go Around)
- WS (Wind Shear)
- FLC (Flight Level Change)
- Speed Control – for all other Flight Director Modes
Note that the default operation for the AT is speed control when no AP/FD modes are active.
Electronic Engine Trim/Synchronization System
Trim System
The Electronic Engine Trim System (EETS) is designed to command limited authority thrust changes via ARINC 429 commands transmitted to the FADECs. The trim system performs TRA trimming to assist the AT, as well as the pilot, at setting trimmed thrust when the system is selected to do so. In addition the trim system will perform N1/N2/EPR synchronization when selected by the pilot.
The EETS is a dual system and is integrated with the dual AT system. Selection logic is located within the Fault Warning Computers to select the single set of trim commands to be transmitted to the FADECs.
The limited authority trim command consists of three components, added together to form a composite trim command, as follows:
- Sync command for N1 or N2 speed synchronization between engines
- TRA trim command for synchronization for EPR command between engines
- TRA position error trim command to account for throttle positioning inaccuracies when AT is engaged (commanded vs. actual)
Synchronization System
The engine trim operating modes (N1 sync, N2 sync, EPR sync and OFF) are pilot selectable via an entry on a CDU page displayed by the priority FMS. Only one mode can be active at a time. Selection of an operating mode arms the sync system for engagement, to provide sync control, when the conditions and flight phase are appropriate to do so.
N1 synchronization is selected as the default setting when the FMS is powered up. Engagement logic to determine when each of the three trim command components are computed (non-zero) is based on the engine trim selected operating mode, AT engagement status and phase of flight.
The engine Synchronization system will compare engine speeds and for the selected shaft synchronization, compute a TRA trim value. The trim value (left-right) is transmitted to each channel of the EEC via ARINC 429. The trim value is added to the RVDT TRA value to generate the overall EEC EPR command in order to match the two engine speeds.
The following data is used by the Integrated Avionics Computer (IAC):
- N1 shaft speed
- N2 shaft speed
- EPR Command (EPR validated)
The EEC limits the trim authority to 5%. The trim authority is washed out at max power and idle setting.
Engine synchronization will operate with or without AT engagement and can be selected by the pilot during takeoff but is inhibited below 400 feet AGL.
N1/EPR Engine Control Panel
The engine electronic controller (EEC) has two modes of operation (to set stable condition power) as follows:
- Engine Pressure Ratio (EPR)
- N1
The primary mode to set stable condition power above idle is EPR.
The EEC starts a reversion to Alternate Control Mode (N1) when it senses failures which prevent continued operation in primary EPR control mode. This is called a soft reversion. When started, a soft reversion is latched and can only be reset in the conditions that follow:
- The fault that caused the reversion has gone
- The pilot sets the applicable engine switch to EPR
The N1/EPR ENGINE control panel has two N1/EPR switches (one for each engine). If one engine makes a soft reversion to N1 control, you should set the other engine to N1 control to prevent asymmetric thrust.
Note:
The EEC controls soft reversions. The N1/EPR switches control hard reversions.
