11.12 - Ice and Rain Protection Flashcards
How does ice affect an aircraft in flight? (6)
- It can change the wings shape resulting in a decrease in lift and increase in drag
- It can change a propeller’s shape and decrease propeller efficiency
- Ice can block movement of control surfaces leading to loss of control
- Ice build up can cause an increase in aircraft weight resulting in a loss of height
- It can block important instruments such as pitot/static ports
- Loss of vision through the cockpit windshield may also occur as a result of ice build up
List the different types of ice? (5)
- Clear (Glaze) ice - dense clouds - remains liquid until runs back over surface until lost enough heat to freeze - continuous smooth layer
- Rime ice - Opaque ice formation
- Gleam ice - complete freezing of the water particles on impact takes longer than in case of rime ice
- Dry ice - forms above 40000 ft unusually
- Hoar Frost - white feathery coating
Differentiate between anti icing systems and de-icing systems?
An anti-icing system prevents the formation of ice, it is engaged before encountering icing conditions. It should always be engaged during flight for example heating of a pitot tube.
A de-icing system removes ice after it has formed on an aircraft, this system is toggled on and off periodically allowing an acceptable level of ice to build up before being removed.
Briefly describe the operation of a pressure operated ice detector?
A pressure operated ice detector is mounted into the airstream. One big hole is drilled into the leading edge and connected to the upper diaphragm. Multiple small holes are also drilled into the leading edge and connected to the lower diaphragm. The area of the combined small holes is larger.
RAM air pressure through the larger area of the small holes keeps a pressure switch open under no icing conditions. Under icing conditions, the small holes freeze up and block first causing a reduction in RAM air pressure and the pressure switch closes due to higher pressure through the big hole. This switch energises a warning relay warning the crew, a heater heats the detector after 60 seconds removing ice and readying the detector once again.
List three systems for de-icing the leading edge of a wing?
- Thermal systems (hot air)
- Electrical systems (heaters)
- Pressure systems/ mechanical (deicer boots)
Describe a vibrating rod ice detector?
This ice detector consists of a probe which is exposed to the airflow. A rod on the probe vibrates ultrasonically at a set frequency driven by a driver coil. This vibration frequency is monitored and in the event of ice accumulation, it’s weight will change and thus alter the vibration frequency. This will activate an ‘’ICE DETECTED’’ warning for the crew which will stay on until anti-ice systems are toggled. A heater in the probe will melt the ice and reset the detector.
When there is no ice build-up, the vibration frequency is within pre-defined limits and ‘’NO ICE DETECTED’’ is shown on the warning display.
Describe how a radioactive ice detector operates?
A stream of radioactive radiation (beta particles) is sent through the ice sensing surface to the GM (Geiger Mueller) tube. Under no icing conditions, the beta particles travel through air and are absorbed by the GM tube.
However, under icing conditions, the ice sensing surface accumulates ice and some beta particles are absorbed by the ice and the beta particles absorbed by the GM tube drops to a predetermined level (ice thickness 0.4 mm). This activates an ‘’ICE’’ warning signal in the cockpit and simultaneously the controller heats a heater which melts the ice, resetting the system and cancelling the warning
What are the precautions for using rain repellent on the ground?
Rain repellent should not be discharged onto a dry windshield as it will smear and become difficult to remove.
Also, if there is insufficient rain, it will not spread out easily and will obstruct visibility.
Rain repellent can only be used on the ground with windshield wipers operating, a sufficient level of rainfall or the windshield being flushed if required for maintenance purposes.
What probes are heated and which of them is not heated on the ground?
TAT is the probe not heated on ground. All probes High Power in Flight. All probes except TAT on Low power on ground.
What is the purpose of water and drain heaters?
Water and drain heaters are used in cold areas of the aircraft where freezing might occur, if freezing occurs in toilet drain lines, water lines, drain masts or waste water drains, it can lead to cracks resulting in leaks which must be avoided.
Describe the operation of a serrated rotor ice detector?
A serrated rotor shaft is adjacent to a fixed knife edge cutter with minimal clearance between the two. The shaft axis is at 90 degrees to the airflow and is continually driven by an electric motor.
Under no icing conditions, the shaft requires minimal rotational torque. However, Under icing conditions, ice accumulates on the shaft and in order for the knife edge to shave off the ice, greater rotational torque is required. This leads to the electric motor rotating slightly in it’s flexible mounting and this movement is sensed and gives an ‘‘ICE’’ warning which remains as long as the ice is being cut by the cutter.
Why can’t pneumatic de-icing be used on the ground?
The engines must be running in order to use compressed air from the pressurised side of an engine vacuum driven pump or compressor stages to inflate the outer tubes to breakup the ice.
Pneumatic de-icing cannot be used on ground as this requires the engines to be running at a relatively high power.
(c) de-icing system
(a) anti-icing system
(b) the lift decreases
(a) isopropyl alcohol and ethylene glycol
(c) to visual monitoring ….
'’Ice detection spot lights illuminate a part of the aircraft that is susceptible to icing (e.g. wing or engine nacelle), this allows the flight crew to visually monitor ice build up’’
(b) never be sprayed on a dry windshielf
(b) the protection covers must be removed prior probe heat system operation
(b) prior flight simulation on ground or aircraft jacking the heater circuit breakers must be pulled to prevent overheating
'’Some heaters have higher power settings in flight’’
(c) Ethylene glycol
(c) It is on constantly during flight
Will have to get clarified by Kevin
(b) They are heated electrically
(a) 1 second
NEED TO DOUBLE CHECK
(c) By breaking up ice formations
(c) When the window is dry
(a) When the glass is wet
'’Chemical rain repellent should not be discharged onto a dry windshield because it will smear and be difficult to remove. It can restrict visibility if it is sprayed on the windshield when there is not enough rain to allow it to be spread out smoothly’’
(a) Total air temperature (TAT)
'’Probes and static ports are automatically heated when an engine is running or the aircraft is in flight condition. The PROBES / WINDOW HEAT P/B overrides the automatic operation.
On ground, pitot heating is reduced and TAT heating is cut off.’‘
