Overview
The detection system detects ice which can collect in certain areas of the aircraft. The system transmits data to the bleed management controllers (BMCs) which supplies a signal to automatically start the wing and cowl anti-icing systems.
The aircraft is fitted with two independent ice detectors, one on each side of the front fuselage below the cockpit side windows.
The detection system continuously monitors the actual condition of the two ice detectors to prevent transmission of incorrect data on icing condition to the bleed management system. The detection system controls the detection of ice and the operation of the related anti-icing systems through the BMCs. For flight safety in icing conditions, the system is connected to the stall protection system.
It sends CAS messages to the engine indication and crew alerting system (EICAS) when icing conditions occur.
Cockpit controls are provided to manually select the anti-ice systems on/off.
Ice Detectors
One ice detector is installed on each side of the aircraft below the cockpit side window panels.
Each ice detector has a probe. The probe is a tube installed in a strut which also includes a magnet, a drive coil and a pick-up coil. The drive coil is installed around the lower half of the tube. A strut heater and a probe heater are installed in the head of the ice detector body. The ice detectors probe uses magnetic properties for analysis of the icing conditions.
The ice detector probe vibrates at a rest frequency of 40,000 Hz. This is caused by the effect of a variable magnetic field supplied by the magnet and the drive coil. The axial vibration of the tube induces a current in the pick-up coil. This current drives an electronic comparator, which sends a signal to the drive coil.
When the ice detector is in icing conditions, the probe in contact with the air collects ice. The added mass of the ice decreases the oscillation frequency of the probe (A measured frequency shift of 130 Hz is equal with an ice thickness on the probe of approximately 0.020 in (0.508 mm)). This is the set ice buildup limit. This frequency is monitored by the ice detectors software which start the ice detector heaters to remove the ice from the probe every time the ice buildup limit is reached.
Heaters are on for 5-20 seconds. The heaters are then turned off, the probe cools and starts to buildup ice again. The ICE outputs will stay active until approximately 60 seconds after the ice buildup limit was last reached.
05/16/16
Bleed Management Controllers
The ice detection system uses two independent ice detectors connected together through the bleed management controllers (BMCs) to give two analysis of the icing conditions. Each ice detector sends the “ICE 2” and “ICE 3” signals to the control and monitoring channels of the BMCs.
When the "ICE 2" signal is sent its related cowl anti-icing system automatically starts. When the "ICE 3" signal is sent its related wing anti-icing system automatically starts.
Each BMC supplies a different signal to open each anti-icing modulating-and-shut-off valves. In the same manner, when one of the two ice detectors sends an "ICE 2" signal, the cowl anti-icing system automatically starts. Each BMC sends a different signal to open each cowl anti-icing valve. In the two cases, the advisory "ICE" message is shown on the EICAS primary page.
A warning "ICE" message is shown if the wing or cowl anti-icing system is OFF. An advisory "ICE" message is shown if the wing or cowl anti-icing systems are ON.
The ice detectors also send an "ICE 1" and a "STATUS" signals to the stall protection computer. The signals give different parameters to the "stick shaker" control. These parameters adjust to the different icing conditions and to the condition of the wing anti-icing system, even when the wing anti-icing system is not in operation.
After take-off, if one of the two ice detectors sends the "ICE 1" signal, the wing anti-icing system automatically starts.
A cautionary "ICE DETECTOR FAIL" message is shown on the primary page of the EICAS if there is a failure of the two ice detectors. An advisory "ICE DETECTOR FAULT" message is shown if there is a failure of one ice detector. In the two cases, the wing anti-icing system and the cowl anti-icing systems must then be started manually with the ANTI-ICE WING or the ANTI-ICE L/COWL or ANTI-ICE R/COWL switch on the BLEED/AIR COND & ANTI-ICE panel.
System Operation
Ice Detection/Anti-Ice Activation
The ice detector uses an ultrasonically axially vibrating probe to detect the presence of icing conditions. The sensing probe is a nickel alloy tube mounted in the strut at its midpoint (node) with one inch exposed to the air stream. This tube exhibits magnetostrictive properties: it expands and contracts under the influence of a variable magnetic field. A magnet mounted inside the strut and modulated by a drive coil surrounding the lower half of the tube provides the magnetic field.
When the ice detector is in icing conditions, the probe collects ice. The added mass of the ice decreases the oscillation frequency of the probe.This frequency is monitored by the ice detector software, and once a preset amount of ice is formed, the ice detector cycle is triggered.
The ice detector cycle is as follows:
- 1. Ice detector is activated after a buildup of approximately 0.020 inch of ice
- “ICE” signal is produced
- Ice detector probe is heated to remove ice for 5 to 20 seconds
- Probe frequency returns to normal, heat is removed and probe cools off
This ice detector cycle is repeated as long as the ice detector remains in an icing environment. The“ICE” signal continues for an approximately 60 seconds from the last activation.
The ice detectors generate three discrete “ICE”signals:
- Ice detector status (BMC for fault indication)
- Ice signal 2 (dedicated to cowl anti-ice)
- Ice signal 3 (dedicated to wing anti-ice)
With the anti-ice panel switches in the AUTO position, and upon receiving the ice signals, the wing and cowl anti-icing systems are activated automatically.
System Monitoring
Power-On Built-In Test
Power-on built-in tests (PBITs) are performed automatically on power-up.
The following tests are performed during PBIT:
- Memory Tests - RAM, ROM, NOVRAM
- Activation/Deactivation test of strut and probe heaters
- Power Monitor Test
Detected faults are latched. Normal operation of the ice detector can only be restored by removing the failure and interrupting power for more than 2 seconds.
Continuous Built-In Test
The detection system continuously monitors the actual condition of the two ice detectors to prevent transmission of incorrect data on icing condition to the bleed management system.
During each program cycle the frequency is measured and compared to the normal operating frequency (40,000 Hz). If the frequency is above 40,150 Hz, a failure output is generated. If the frequency falls 130 Hz the ice detector goes through a normal icing cycle. After the heater has tried to melt the ice unsuccessfully for 10 seconds and the frequency is still below 39,870 Hz, the heater and ice output are turned off, the failure signal is activated and the failure is logged in RAM.
Every 60 seconds a comprehensive test is performed on the ice detector circuitry. The heater is tested by pulsing it on for 400 ms. The failure and icing signal outputs are also pulsed to verify each state. This test also verifies proper operation of the microcomputer.
If a failure is detected, the BMCs generate a CAIMS fault and a CAS message.
System Test
Initiated Built-In Test – CAIMS
The ice detectors can be tested via CAIMS. During the bleed management controller (BMC) IBIT, the ice detectors are tested.
If the system passes the test, a “Test Results: Pass”message will be displayed (on the PMAT). If a failure occurs, the appropriate CAIMS message will be generated, and for certain failure conditions, a CAS message will also be generated.The CAIMS report will identify the failed LRU.
Ice detector data is displayed on the left and right BMC: bleed management status page. The real time data will display current operating status as follows:
- Ice detector status (OK or failed)
- Ice signal 2 status (ice or no ice)
- Ice signal 3 status (ice or no ice)
