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Flashcards in Pitot/Static Flight Instruments Deck (12)
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What instruments operated off of the pitot/static system?

Altimeter, Vertical Speed, and Airspeed Indicator


How does an altimeter work?

Aneroid wafers expand and contract as atmosphere pressure changes, and through a shaft and gear linkage, rotate pointers on the dial of the instrument.


What are the limitations of a pressure altimeter?

Non-standard pressure and temperature variations expand or contract the atmosphere and raise or lower pressure levels that the altimeter senses.

a) On a warm day - The pressure level is higher than on a standard day. The altimeter indicated lower than actual altitude.
b) On a cold day - The pressure level is lower than on a standard day. The altimeter indicates higher than actual altitude.

Changes in surface pressure also affect pressure levels at altitude.

a) Higher than standard pressure - The pressure level is higher than on a standard day. The altimeter indicates lower than actual altitude.
b) Lower than standard pressure - The pressure level is lower than on a standard day. The altimeter indicated higher than actual altitude.

REMEMBER: High to low or hot to cold -- Look out below!


Define absolute altitude

The vertical distance of an aircraft above the terrain


Define indicated altitude

The altitude read directly from the altimeter (uncorrected) after its set to the current altimeter setting.


Define pressure altitude

The altitude when the altimeter setting window is is adjusted to 29.92. Pressure altitude is used for computer solutions to determine density altitude, true altitude, true airspeed, etc


Define true altitude

The true vertical distance of the aircraft above sea level. Airport, terrain, and obstacle elevations found on aeronautical charts and true altitudes.


Define density altitude

Pressure altitude corrected for non-standard temperature variations. Directly related to an aircraft's takeoff, climb and landing performance.


How does the airspeed indicator operate?

The airspeed indicator is a sensitive, differential pressure gauge which measures the difference between impact pressure from the pitot head and undisturbed atmospheric pressure from the static source. The difference by the airspeed pointer on the face of the instrument.


What are the different types of aircraft speeds?

a) Indicated airspeed (IAS) - the speed of the airplane as observed on the airspeed indicator. It is the airspeed w/o correction for indicator, position, or compressibility errors.
b) Calibrated airspeed (CAS) - the airspeed indicator reading corrected for position (or installation error) and instrument errors. CAS is equal to TAS at sea level in standard atmosphere. The color-coding for various design speeds marked on the airspeed indicators may be IAS or CAS.
c) True airspeed - CAS corrected for altitude and non-standard temperature. Its the speed of the airplane in relation to the air mass in which it is flying.


Name several important airspeed limitations not marked on the face of the airspeed indicator

a) Design maneuvering speed (Va) - the maximum speed at which the structural design's limit load can be imposed w/o causing structural damage.
b) Best angle of climb speed (Vx) - important when a short-field takeoff to clear an obstacle is required.
c) Best rate of climb (Vy) - the airspeed that will give the pilot the most altitude in a given period of time.


How does the vertical speed indicator work?

The vertical speed indicator is a pressure differential instrument. Inside the case, is an aneroid very much like the one in the airspeed indicator. Both the inside of this aneroid and the inside of the instrument case are vented to the static system, but the case is vented through a calibrated orifice that caused the pressure inside the case to change more slowly than the pressure inside the aneroid. As the aircraft ascends, the static pressure becomes lower and the pressure inside the case compresses the aneroid, moving the pointer upward, showing a climb and indicating the number of feet per minute the aircraft ascending.

The VSI is not accurate unless the aircraft is stabilized.