Section of 14. Ice and Rain Protection

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Madeleine Craig
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1 Ice & Rain Protection 1 of 14

2 WINDSCREEN WIPERS General The aircraft is fitted with two windscreen wipers, one on each pilots side windscreen, which are controlled by a 3-position (FAST, SLOW and MANUAL) speed selection switch on the 34 panel and an /OFF push button on each collective lever. Either button operates both wipers. A 28V DC motor drives both wipers via gear boxes which convert the rotary motion of the motor to reciprocating motion using a rod and crank system. The motor is supplied by 2PP6 bus bar. A windscreen washing system is also fitted with its spring loaded control switch on the 34 panel. Power supply for the pump is from 2PP5 bus bar. The reservoir is situated under the cabin floor with its filler neck under the Radome on the left-hand side of the aircraft. Control PCB Low Speed Resistor Wiper Blade Wiper Arm Gearbox Flexible Drive Flexible Drive Double-Output Motor /OFF Button Windscreen Wiper Control Switch WDSCR WIPERS LATER MAN F S WDSCR WASH Figure 1 Windscreen Wiper Components Windscreen Wash Control Switch 2 of 14

3 Wiper Operation Speed Switch to FAST Making and releasing either switch on the collective levers will start the motor and the wipers will operate at 175 cycles per minute over an arc of 53. Making and releasing either button again will cut off the supply to the motor and, via a delay logic and limit switch, the wipers will 'park' in the horizontal position. Speed Switch to SLOW The operation is the same as in FAST position except that a resistor in the circuit reduces power to the motor and the wipers operate at 140 cycles per minute. Speed Switch to MANUAL With the selector switch in this position the wipers will work at slow speed only whilst an /OFF button is held depressed. Releasing the button stops the wipers at whatever position they happen to be at the time. Washer Operation Holding the switch in the UP position starts the pump and the washing fluid is pumped up from the reservoir to the spray jets below the windscreen. The pump stops when the switch is released. WINDSHIELD HEATING General The lower portions of the Pilot s and Co-pilot's windscreen panels are fitted with electrically heated grids to prevent formation of Ice and mist. The panel assembly consists of two specially treated heat-resistant glass panes with a plastic layer bonded in between. A Heating grid and two temperature sensors are embodied between the glass panes with only one of the sensors being connected to the electrical system. The other is a standby. In the event of failure of the first a simple change over connection can be made. Each heating grid is supplied with 3-phase AC power with a regulator and a transfer PCB which ensures correct operation of each heating element if one regulator fails. The 3-phase power supplies for the left-hand windshield heating is from 1XP1 (phase A, B and C) and for the right-hand windshield heating 2XP1 (phase A, B and C). DC power for the relays is from 1PP6 for the right-hand circuit and 2PP5 for the left-hand circuit. The regulator maintains the heating element temperature between 25 and 30 C. Central windshield heating can be fitted as an option. 3 of 14

4 Right-Hand Heated Windscreen Left-Hand Power Supply Relay Left-Hand Heated Windscreen Right-Hand Power Supply Relay WSHLD ANTI-ICING WDSCR LH WDSCR RH OFF OFF Figure 2 Windscreen Heat Components 4 of 14

5 INTENTIALLY BLANK 5 of 14

6 Controls & Indications The /OFF control switches for each windshield heater are on the 34 panel with a warning light above each switch. A WSHLD light on the 32 panel and the light above the relevant switch on the 34 panel will illuminate if a fault occurs whilst the system is switched. Both lights will extinguish when the switch is made OFF but the heating will still be supplied under control of the other windshield heating regulator. A test facility is fitted to the PCB for engineering purposes. The location of controls and indications are shown in Figure 2. Operation Refer to Figure 3. When the 34 panel switch is made the 28V DC from the bus bar will energise the safety relay (K1) via the Safety and Transfer logic PCB. The Regulation Relay (K2) will also be energised if the temperature of the heating grid is below 25 C. Making these two relays energises the switching relay (K3) which makes the contact for the 3-phase AC power to flow to the heating grid. When the temperature sensor, controlling the regulation PCB, senses a grid temperature of 30 C the regulation relay (K2) will be de-energised and the supply to the switching relay will be broken. The switching relay will de-energise, cutting off the 3-phase supply to the heating grid. As the temperature falls to 25 C the cycle will be repeated. Should a fault occur in the logics, regulation circuit or temperature sensing circuit the Safety & Transfer PCB will break the supply to relay (K1) and it's two contacts will move to their rest positions. One contact will make an earth for the 34 panel warning light and the WSHLD light which both illuminate. The second contact makes a supply from the other windscreen heating circuit to the switching relay which then operates under control of the regulation relay of that windscreen. Switching OFF the 34 panel switch will extinguish both warning lights but the windscreen heating will continue to be supplied as directed by the serviceable circuit. 6 of 14

7 PP5 WDSCR LH WSHLD WDSCR RH 2PP6 Left-Hand Anti-Icing Switch Right-Hand Anti-Icing Switch 2XP1 1XP1 Regulation Safety & Transfer Safety & Transfer Regulation K1 K1 K3 K3 K2 K2 S1 S2 Left-Hand Windscreen Right-Hand Windscreen Figure 3 Windscreen Heat Electrical Circuit 7 of 14

8 ICE DETECTI General The AS332L is fitted with a Leigh Mk 12 ice detection system which consists essentially of a probe, mounted on the right-hand side of the aircraft behind the Pilot's door and a control panel mounted on the right-hand side of the centre console. This unit measures the liquid water content (LWC) of the atmosphere the aircraft is flying in and displays this information in grams per cubic metre on a gauge on the control panel. The Leigh Mk 12 ice detection system is designed to detect icing conditions existing at the mid point of the rotor blade, not airframe icing. Airframe icing is detected and measured on a fixed probe and disc extending from the Captain's door (as shown below). 4cm Figure 4 Fixed Ice Probe with Maximum Ice Accumulation The disc on the fixed ice probe has a series of rings marked at 5 and 10mm intervals out to 40mm. Any ice build up on the fixed probe is measured against the rings on the disc. The maximum ice deposit as allowed by the Flight Manual is 40mm. The disc can be illuminated at night by means of a light on the inside of the Captain's door. The control panel has two warning lights (Icing and Fault), an /OFF switch with power light, a test switch and a liquid water contents gauge reading from zero to 1.0 grams per cubic metre. On the 32 panel an amber warning light ICE.D will illuminate if the Icing or Fault' lights on the control panel Illuminate. The limitations regarding severity of L.W.C. and icing conditions are contained in the Flight Manual supplement These controls and indications are shown in Figure 5. 8 of 14

9 ICE D Central Warning Panel ICING FAULT POWER TEST LWC 0 TEST LWC G/M³ 1. OFF Figure 5 Ice Detector Monitor Panel Operation of Leigh Ice Detector Unit The detection unit consists of an aspirated venturi duct mounted on a mast through which is passed P2 air (at 4.5 bar pressure) from the engines. The P2 air passes to a plenum chamber in the nose of the duct and flows out via annular slots along the inside edge of the duct. This air, being hot, keeps the mast, nose cap and duct ice free. The flow of P2 air induces ambient air, with its water content, to flow through the duct and across the face of a sensor probe. The adiabatic expansion within the throat of the duct causes a reduction in temperature of the ambient air at the sensor probe allowing it to be used at temperatures of 0 C and above. The design of the nose cap ensures a reasonably constant velocity of air through the duct, irrespective of forward air speed, thus maintaining accuracy of the system. The sensor probe is a thin walled (0.006 ) inconel tube with a flattened front face, to ensure better ice accretion, through which can be passed a low voltage AC heating current. (1 Volt - 30 amp). A Light Emitting Diode sends an infra-red beam diagonally across the front face of the sensor to a Phototransistor which, in turn, controls the heating and indications computer housed in a box at the base of the mast fitted between the airframe skin. 9 of 14

10 To maintain the cleanliness of the optical system, ambient air, from a vent below the mast, is drawn across the optics by the P2 airflow. Included in this ambient air line is a filter and a water trap. Should the P2 air temperature be below +5 C a 350 watt 115V AC heater, controlled by a thermistor in the tail of the duct, will be switched on. A pressure switch set at 0.7 bar (10-psi) cuts out the heater circuit when P2 air pressure is below this figure to safeguard the heater. The system includes a built in self-testing circuit, which operates every 8.2 milli-seconds, with a pre-flight testing switch. Light Emitting Diode Sensor Probe P2 Air Gas Stream Nose Cap Photo Transistor Thermistor Mast P2 Air Supply at 4.5 bar Ambient Air Supply Figure 6 Leigh Ice Detector Operation Should any icing conditions be encountered the ice will build up on the front face of the sensor probe and begin to block the path of the infrared beam. When the ice is 0.005" thick a timer circuit is started and, as the ice thickness increases, the beam is gradually occluded until at 0.010" thickness, the icing light illuminates, the heater is switched and the sensor probe is rapidly heated up to shed the ice. The timer is stopped but the heating continues for approximately half a second after the ice is cleared below the 0.005" thickness threshold. When the heating is switched OFF the sensor cools rapidly and the cycle is repeated for as long as icing conditions exist. The computer uses the timer circuit to determine the amount of LWC in the atmosphere (i.e. 20 seconds means low LWC whilst 2 seconds mean high LWC) and displays this information on the LWC meter. Whenever the upper threshold (0.010") is reached the LWC meter reading is updated. On leaving icing conditions the meter reading will reduce, being near to zero after 60 seconds, at which point the icing light will be extinguished. Should a fault occur in the system during use, the built-in test will cause the 'fault' light to illuminate and the LWC to give full scale deflection. If the fault renders the system inoperative it will automatically be shut OFF and the fault light remains illuminated. Should the fault be of transitory nature the system will be restored to normal operation when the fault has cleared. Such a fault could be an ice particle lodged in the duct, which has not melted after 5 seconds. When the particle finally melts normal operation of the system will be restored and the 'fault' light extinguished. Should the 115V AC power supply from 1XP2A fail, the ICE.D caption will illuminate and the green power light will extinguish. 10 of 14

11 Operating Procedures The system should be switched after both engines started and a pre-flight test carried out after 10 seconds. When the test switch is set to TEST the 'icing' and 'fault' lights illuminate, along with the caption on the 32 panel. The LWC meter gives a full scale deflection. After 4½ seconds the lights will extinguish and after a further 4½ seconds the LWC meter reverts to it's original reading. This test can be carried out at any time after 10 seconds from switching, without affecting the operation of the system. A Flashing 'fault' light at initial switch is an indication that the system is trying to clear a fault (such as a dust particle on the optics). Should the fault not clear after 2 minutes, the system may be re-set by switching OFF for 10 seconds and then again. If the fault continues after two attempts at resetting, the unit is unserviceable. Should a fault occur in flight, which does not clear after 2 minutes, the resetting procedure may be attempted. The 'fault' light will also flash if the sensor probe falls to de-ice after 6½ seconds during normal operation. To prevent ingress of particles into the optical system it is essential that the dust cover be fitted during aircraft washing. The cover must be removed for compressor washing procedures and the unit switched during the drying run to ensure no moisture remains in the system. 11 of 14

12 ENGINE INTAKE ANTI-ICING General To prevent accretion of ice at the back of the intake grids, heating mats are fitted to the inner wall of the forward sliding intake cowling. There are two mats to each intake with each pair of mats having three heating resistor elements. The resistors are star connected with each resistor having a different supply from the 115V AC bus bar 1XP2 via protection circuit breakers. Two DC powered relays (one for each intake) control the three single-phase supplies to the resistors with the power supplies for these relays coming from PP4 bus bar via protection circuit breakers. A control panel is installed to enable /OFF switching and TEST facilities with warning lights for correct operation or failure. The system includes a safety device to prevent the heating being switched whilst the engines are shut down. ENGINE AIR INTAKE ANTI-ICING ENGINE 1 TEST ENGINE OFF R2 OFF 1 R1 R3 1 4 DE ICE 1. /OFF Control Switch 2. Amber Failure Warning Lights 3. /OFF Test Switch 4. Rotary Selector Switch 5. Green Test Correct Lights Figure 7 Intake Anti-Ice Components Limitations 1. The fitting of heating mats makes no changes to the limitations given in the Flight Manual. 2. Maximum OAT for continuous use is +10 C 3. System should be switched with OAT of +5 C and in visible moisture. Controls and Indications Refer to Figure 7. The control panel is located on the overhead panel. It consists of two /OFF control switches (one for each engine) with amber warning lights to denote a failure of a system. There is a single /OFF test switch with two green lights and a rotary selector switch to enable testing of each resistor circuit in turn. 12 of 14

13 An amber DE ICE light on the 32 panel will illuminate if either of the two amber fault lights on the control panel illuminate. System Operation Refer to Figure 8. The system for one engine is shown in the operating condition with the Control Switch and the Test Switch OFF. The other engine system is similar. The power supply from PP4 passes through the Test Switch OFF contact, through the Control Switch contact, to energise the heating relay and making its 4 contacts to the positions shown. The 3 single-phase supplies are connected to the heating resistors. A phase detector monitors the 3 supplies and if one phase loses voltage, it will illuminate the amber failure light and the DE ICE caption. If the system is now switched OFF these lights will be extinguished. An open circuit in one resistor will not be indicated until a test is carried out. When the Test switch is made the power to the heating relay is cut off and directed to the Rotary Selector Switch. The current can now pass through the relevant resistor (the heating relay contacts being in their 'rest' position) and back to earth via the second contact of the Test Switch to illuminate the green test correct light. If the green light fails to illuminate then there is a break in the circuit. Note that if the test is carried out with the Control Switch then the amber failure light and DE ICE caption will also illuminate due to the earth contact of the de-energised heating relay. To ensure the heating relay cannot be energised until the engines are running the earth for the heating relay is broken until the oil pressure exceeds 1.7 bar and the ENG P light extinguishes, controlled by the pressure switch on the relevant engine. When the engines are running the systems should be switched (if required) and the failure lights and caption should remain extinguished. System Testing The Test Switch and Rotary Selector can be used at any time before or after engine start up. With the Test Switch the green test correct lights should both illuminate in each of the 3 positions of the Rotary Selector. 13 of 14

14 Upper Intake Mat A B C Lower Intake Mat 1XP Phase Detector R1 R2 R3 Rotary Selector Heating Relay P P 4 Test Switch OFF Heating Switch OFF ENG P Light Out when pressure > 1.7 bar TEST FAULT DE ICE + + Figure 8 Intake Mat Electrical Circuit 14 of 14

Fokker 50 - Ice & Rain Protection. Controls and indicators of the AIRFRAME DE-ICING system are located at the ice protection panel.

Fokker 50 - Ice & Rain Protection. Controls and indicators of the AIRFRAME DE-ICING system are located at the ice protection panel. ICE AND RAIN PROTECTION AIRFRAME DE-ICING Description Controls and indicators of the AIRFRAME DE-ICING system are located at the ice protection panel. Airframe de-icing is accomplished by alternately inflating