12.38.2. Given a sample deviation card, show how to apply corrections.
The amount of deviation on different compoass headings differs from aircrft to aircraft and can be determined through a procedure called a compass swing carried out on the particular aircraft
The results of the compass swing and any compensation taken for deviation are shown on a deviation card displayed in the cockpit
Corrections to the compass heading amy be applied to obtain an accurate magnetic heading
12.36. Pressure Instruments
12.36.16(b) . blockage of the static source.
Indications
– if anything bllocks the static vent, air will be trapped in the static line and all 3 pressure instruments will be affected
– ASI shows lower speed than actual during a climb and higher than actual during a descent
– altimeter will indicate a constant altitude despite aircraft climbing/ descending
– VSI – will read zero even though may be climbing / descending
Actions
12.36.16(a) . blockage of the pitot tube;
Indications
– only the ASI will be affected
– in level flight change in airspeed will not be registered by ASI
– in a climb ASI will be too high
– descent below icing – ASI too low
– if not ice blocking – ASI will have continued to be zero on take off
Actions
– clear any ice by switching on the pitot heater
– if no heater try a descent to a warmer altitude
– use pitot heat normally if going through cloud or heavy precipitation
– if something else causing the blockage ASI will be zero on take -off – so this can be aborted – or declare an emergency
12.36.16. Identify the cockpit indications of the following pitot-static system malfunctions,and state the actions available to the pilot to deal with the problem:
(a) . blockage of the pitot tube; |
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Indications – only the ASI will be affected – in level flight change in airspeed will not be registered by ASI – in a climb ASI will be too high – descent below icing – ASI too low – if not ice blocking – ASI will have continued to be zero on take off Actions |
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(b) . blockage of the static source. |
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| Indications – if anything bllocks the static vent, air will be trapped in the static line and all 3 pressure instruments will be affected – ASI shows lower speed than actual during a climb and higher than actual during a descent – altimeter will indicate a constant altitude despite aircraft climbing/ descending – VSI – will read zero even though may be climbing / descending Actions |
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12.36.14. Indicate the normal checks for serviceability of the pitot-static system, both preflightand during operation.
Pre-flight
– pitot cover removed
– pitot head and static vents checked for damage and blockage
– inspect instruments for damage or malfunction
– ASI and VSI – should read zero
– set altimeter to aerodrome elevation
– take-off run check speed builds on the ASI
– entering climb check the altimeter and VSI showing correctly
During flight
– only adjustment would be to the altimeter subscale after getting amended QNH
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12.36.12(b) . errors affecting the VSI.
VSI Errors
Lag
– main cause of error in a pressure operated VSI
– to get accurate rate of cliimb measurement the VSI must be allowed to settle after the aircraft attitude is changed
Position Error
– occurs through fluctuations in pressure sensing at the static vent
– even if the aircraft is level
– inherent limitation of the instrument
12.36.12(a) . basic principle of operation;
– provides a direct readout of the rate of change of altitude
– pressure instrument that converts a rate of change of static pressure to a rate of change of altitude
– expressed in hundreds or thousands of fett per minute (fpm)
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