12.36.8(b) . colour coding, and the meaning of VSO, VS1, VFE, VNO and VNE; 

Green arc – normal operating speed range
Yellow arc – caution range
White arc – flaps operating range
Red radial line – never exceed speed

VSO – stalling speed – landing gear down, flaps lowered power off
VS1 – stall speed – landing gear up, flaps up, power off
VFE – maximum speed flaps extended
VNO – normal operating limit speed
VNE – never exceed speed

12.36.8(a) . basic principle of operation and serviceability checks; 

– provides a reading of the airspeed referred to as the Indicated Airspeed IAS
– measures dynamnic pressure acting on the aircraft

Checks
During pre-flight external inspection – check the pitot cover is removed
Chech pitot head and static vents for damage and blockage
ASI should read zero

12.36.8. With respect to the airspeed indicator, describe the:

(a) . basic principle of operation and serviceability checks; 




- provides a reading of the airspeed referred to as the Indicated Airspeed IAS
- measures dynamnic pressure acting on the aircraft
Checks
During pre-flight external inspection - check the pitot cover is removed
Chech pitot head and static vents for damage and blockage
ASI should read zero 


(b) . colour coding, and the meaning of VSO, VS1, VFE, VNO and VNE; 



Green arc - normal operating speed range
Yellow arc - caution range
White arc - flaps operating range
Red radial line - never exceed speed
VSO - stalling speed - landing gear down, flaps lowered power off
VS1 - stall speed - landing gear up, flaps up, power off
VFE - maximum speed flaps extended
VNO - normal operating limit speed
VNE - never exceed speed 


12.36.8(c) . IAS/TAS/groundspeed relationship; 



IAS is the "aerodynamic" airspeed of the aricraft
At low levels of the atmosphere IAS is close to TAS
TAS is the actual speed of the aircraft through the air
It can be calculated by applying a correction for air density to IAS
GS is the speed of the aircraft relative to the ground
It can be calculated by applying W/V to the aircraft heading and TAS 


(d) . errors affecting the ASI, and how position error correction is applied. 



Density Error
- this is the inability of the ASI to take account of the air density variations.
- some ASIs have a small rotatable scale which provides compensation for its density error
Position Error
- if in a high nose attitude the pitot tube and static vents will be at an unusual angle to the oncoming airflow and the way in which they register the pressure may be changed.
Any position error from a high nose attitude is allowed for in the callibration of the Vso and Vs1 marks on the ASI
A posiiton error correction PEC is usually found in the POH (Pilot operating Handbook) - applied to the ASI readout to give the CAS (callibrated airspeed)
Instrument Error
- sometimes wear and tear can cause slight variations in the readings
- only usually amounts to 1-2 knots of error



 
        

         
    

12.36.6(e) . alternate pressure source. 

– enables the pressure inside the cabin to be sensed in the event of ice or other stuff blocking the external vents
– in unpressurised aircraft the cabin pressure is only slightly less than the external atmospheric pressure so the instrument readings will be only slightly errored if the alternate source is selected

12.36.6(d) . drain holes, heating, and pitot cover; 

Drain holes – any water from rain or condensation which collects in the tube can drain out through drain holes
Heating – an element is fitted to the pitot head to clear potentially blocking ice formation
Pitot cover – prevents damage or blackage of pitot tube ffrom insects, dust, rain

12.36.6(c) . combined pitot-static head; 

12.36.6(b) . pitot tube; Sub Topic Syllabus Item 

Pitot tube
– mounted on the wing
– enables total pressure to be measured

12.36.6(a) . static vent(s); 

Static vent
– provides for sensing static pressure

12.36.6. Explain the operation of 
 a pitot-static system, including:











(a) . static vent(s);







- provides for sensing static pressure 










(b) . pitot tube; 






           

           

- mounted on the wing

- enables total pressure to be measured



(c) . combined pitot-static head; 





(d) . drain holes, heating, and pitot cover;


 Drain holes - any water from rain or condensation which collects in the tube can drain out through drain holes
Heating - an element is fitted to the pitot head to clear potentially blocking ice formation
Pitot cover - prevents damage or blackage of pitot tube ffrom insects, dust, rain



(e) . alternate pressure source.


 - enables the pressure inside the cabin to be sensed in the event of ice or other stuff blocking the external vents
- in unpressurised aircraft the cabin pressure is only slightly less than the external atmospheric pressure so the instrument readings will be only slightly errored if the alternate source is selected 



 
        

         
    

12.36.4. Describe static pressure and dynamic pressure, and the main factors which affectthem. 

Static Pressure
– the air exerts a pressure equally in all directions at any point in the atmosphere (static pressure)
– results from the weight of all the air molecules above that point pressing down
– not affected by any air movement

Dynamic Pressure
– any solid body which moves relative to the air surrounding it experiences an additional pressure on the surfaces facing the directin of movement
– this is dynamic pressure and is over and above the static pressure
Depends upon
– the Velocity of the body relative to the air
– the Density of the air