仪表飞行员地面课程Lesson 2

Types of Altitude: (cont.)

Density Altitude
– Pressure altitude corrected for nonstandard temperature. – A theoretical value – not a height! – Used solely for determining performance. – Calculated from flight computer or graph.
Airspeed Indicator
Airspeed Indicator
Types of Airspeed:

Indicated Airspeed (IAS)
– Airspeed that is displayed on the instrument – The greater difference between ram air and static air results in higher IAS
1.
Airspeed Indicator


Uses differential pressure from pitot tube and static port(s) Compares ram pressure to static pressure Internal diaphragm vented to pitot tube; sealed instrument case vented to static port(s) What information does it provide?
Types of Altitude: (cont.)

True Altitude
(cont.)
– When altimeter indicates field elevation with correct local altimeter setting, indicated altitude is the same as true altitude.
Types of Altitude:

Indicated Altitude
– Read directly from the altimeter when it is correctly set to the local altimeter setting.

Pressure Altitude
– Altitude displayed on the altimeter when it is set to 29.92 – Regulations require that we set our altimeter to 29.92 when operating above 18,000 feet MSL.

Calibrated Airspeed (CAS)
– Indicated airspeed corrected for installation and instrument errors (static ports and pitot tube) – This error is relatively small in cruise speed ranges and becomes more of a factor at speed extremes – Determined by looking at calibrated tables in POH
Airspeed Indicator Errors

Usually result from blockage of pitot tube or static port Pitot Blockage (incl. Drain Hole) Airspeed indicator will react like altimeter. Why? Pitot Blockage (Drain Hole Open) Airspeed will drop to zero. Why? Static Blockage Airspeed will indicate lower than what it should at higher altitudes and higher than it should at lower altitudes from where blockage occurs. “Reverse Altimeter”
Types of Altitude: (cont.)

Pressure Altitude
(cont.)
– Altitudes at or above 18,000 feet MSL are called flight levels (FL). – Some flight levels are unusable when pressure extremes occur. See FAR/AIM. – Pressure altitude also used for determining performance.
Altimeter Errors
Friction Error – inherent whenever there are moving parts. Mechanical Errors – misalignment or slippage of gears or linkage Hysteresis – results from expanding and contracting of the aneroid wafers. The aneroid wafers do not return to original size. Scale Error – aneroid wafers do not respond uniformly to local pressure differences. To be considered reliable, altimeter should indicate within 75 feet of field elevation.
Types of Altitude: (cont.)

True Altitude
– Actual height above mean sea level. – Indicated altitude = true altitude in flight only under standard conditions with correct altimeter setting. – Nonstandard temperature and pressure causes indicated altitude to differ from true altitude. – Can roughly be determined with flight computer and/or conversion tables. Assumes standard lapse rates.
Airspeed Indicator
Altimeter (Pressure Sensitive)


Indicates height above whatever pressure level is set in Kollsman window Basic component of the pressure altimeter is the aneroid wafer The sealed aneroid wafers expand and contract as atmospheric pressure changes within the sealed instrument case

Absolute Altitude
– The actual height of the airplane above the earth’s surface – Used to determine DH, HAA, HAT, and TCH on published instrument approaches
Altimeter
Altimeter
Altimeter (Pressure Sensitive) (cont.)


The instrument case is vented to static port(s) Altimeter setting dial provides a means of adjusting the altimeter for nonstandard pressure and pressure differences between locations The scale is usually calibrated from 28.00” to 31.00”. Why? Rotating the setting simultaneously rotates the scale and altimeter pointers at a rate of 1” per 1,000 feet in the same direction
Calibration Tables
Types of Airspeed: (cont.)

Equivalent Airspeed (EAS)
– Calibrated airspeed corrected for the compression of air in the pitot tube at particular altitudes and airspeeds – Not a big factor until reaching altitudes above FL200 and airspeeds above 200 knots – Most aircraft that are affected already have EAS compensated for in their TAS indicators and computers