Speed is the rate of change of position, or distance covered per unit of time. Airspeed gets input from Pitot tube and static air source.It is expressed in linear units per hour. As there are three main linear units, there are three main expressions of speed:
** Knots (kts) - nautical miles per hour
** Miles per hour (mph)
** Kilometres per hour (kph)
The airspeed indicator is used by the pilot during all phases of flight to maintain airspeeds specific to the aircraft type and operating conditions. Is used in addition to the Artificial horizon as an instrument of reference for pitch control during climbs, descents and turns.The airspeed indicator is also used in dead reckoning, where time, speed, and bearing are used for navigation in the absence of aids such as NDBs, VORs and GPS.
***Airspeed Indicator Error Examples:
1) Instrument Error
Resulting from poor design and construction of airspeed indicator (ASI) itself, or from friction within it.
2) Position Error
Resulting from sensing errors inherent in the position on the aircraft of the static vent and pitot tube. Their position with respect to the airflow is critical.
3) System malfunction
Blocked pitot tube is a pitot-static problem that will only affect airspeedindicators. The pitot tube is susceptible to becoming clogged by ice, water, insects or some other obstruction will cause the airspeed indicator to register an increase in airspeed when the aircraft climbs, even though indicated airspeed is constant.This is caused by the pressure in the pitot system remaining constant when the atmospheric pressure (and static pressure) are decreasing. In reverse, the airspeed indicator will show a decrease in airspeed when the aircraft descends.
***Three groups of speed are used in air navigation:
1)Airspeed
The speed of the aircraft through the air
-True Airspeed (TAS)True airspeed (TAS) of an aircraft is the speed of theaircraft relative to the air mass in which it is flying.
-Indicated Airspeed (IAS)
Is the speed obtained through ASI. When the air around the aircraft differs from standard sea level conditions, IAS will no longer correspond to TAS. This is due to nature of atmosphere where the air pressure and density decrease with altitude.
-Rectified Airspeed (RAS)
IAS will produce error due to instrument and position error. Thus RAS is needed to avoid this error. Rectified Air Speed, sometimes known as Calibrated Air Speed (CAS) is IAS corrected for position error.
2)Groundspeed
The speed of the aircraft in relation to the ground
3)Relative Speed
The speed of an aircraft relative to another aircraft
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