Barometric Instruments Flashcards
What are the two most important reasons why the principles of operation and the interpretation and reading of instruments used on modern aircraft needs to be thoroughly understood by the technician?
- Safety
- The instruments can provide the technician with indications of powerplant or system conditions. This data can be used for troubleshooting.
What are the two basic types of mechanical pressure measuring instruments?
Bourdon Tubes & Diaphragm/Bellows
What does the Bourdon tube measure?
Typically used for high pressure readings such as oil pressure and hydraulics.
Can be used to measure low pressures.
What are Bellows or Diaphragms used for?
Used to read comparatively low pressure readings.
What is a sealed aneroid called?
Diaphragm
What is it called when diaphragms (aneroid cells) are stacked?
Bellows
What 3 aircraft instruments are built with bellows and diaphragms and “powered” by air pressures.
Altimeter
Airspeed Indicator
Vertical Speed Indicator
What is the source of “power” for the Altimeter, A/S indicator and VSI instruments?
Pitot-static system
What does the pitot system provide?
Ram air
What does the pitot system consist of?
One or more pitot tubes and various connections and tubing
What is the only instrument that uses ram or pitot air pressure?
Airspeed Indicator
When may a pitot tube be heated?
If the A/C is certified for IFR flight
When is an aircraft not required to have a heated pitot tube?
If the aircraft is certified for VFR flight only
How do you test the heating element on a pitot tube?
Turn on the aircraft, turn on the pitot head, and look for the draw on the ammeter
What does the static system provide?
The static system provides low pressure air to the altimeter and Vertical Speed
Indicator (VSI)
Where are the Static Ports typically located?
Typically located on the side of the A/C fuselage.
May also be located in the pitot head
What is built into the pitot system and static system to prevent water reaching the instruments and causing damage?
moisture drains
What will moisture do to the pitot and static systems?
Cause corrosion and may also freeze at altitude - rupturing lines or or damaging instruments
What type of static drains may be on larger aircrafts?
Petcock type drain valves
The pitot system and static system are completely independent systems but….
both systems are needed to provide readings for the instruments
When inspecting or working on or around pitot or static systems…
care must be taken not to damage the openings to these ports
What must you always use when connecting, disconnecting, or torquing rigid tube fittins?
Two wrenches
What should you never do to pitot static ports?
Never spray water directly into them
What type of damage can cause readings to be incorrect?
Static erosion
Always ensure what before releasing the A/C for flight?
Ensure pitot static ports are clear of covers
What is a required instrument for all aircraft including free balloons?
An Altimeter
Aircraft performance measurement is based on the conditions of what?
A Standard Day at sea level
What is the basic need for an aircraft?
To measure altitude above sea level
What is the temperature and barometric pressure from the Standard Day?
29.92 inches of Hg and 59 degrees F
What is absolute altitude?
The vertical distance of the aircraft above terrain
What is indicated altitude?
Altitude read directly from the altimeter (uncorrected) after it is set to the current barometric setting
What increments do altimeter pointers register?
hundreds, thousands, ten thousands
What does the short and fat pointer register in?
Thousand
What does the longer pointer register in?
hundred
What is the smallest pointer registered in?
ten thousand
What is another feature of the altimeter?
Kollsman window and temperature compensation
How do cold fronts affect the aircraft?
Cold fronts have denser hair and the aircraft true altitude may be lower than the indicated altitude
How do warm fronts affect the aircraft?
Warm front has less dense air and the aircraft’s true altitude may be higher than indicated altitude
What are the two basic types of altimeters?
Non-sensitive and sensitive altimeter
How many pointers does the sensitive altimeter have?
3
All a/c flying at or above ____ are required to what to their altimeter?
flying above 18k ft are required to set their altimeters to 29.92 inches of Hg
What is a flight level?
At 18k ft and higher
What is the pressure altitude of flight level 300?
30,000
Some aircraft measure barometric pressure in…
millibars or pascals
What does the encoding altimeter provide?
Provides a signal that is sent to Air Traffic Control (ATC) to display aircraft altitude on the ATC radar screen
The encoding altimeter works in conjunction with that aircraft’s…
Transponder
On many light a/c the encoder is…
a separate piece of equipment from the altimeter or transponder
What does 91.411 state?
Altimeter testing must be conducted every 24 calendar months
Transponders altitude reporting must be accomplished according to what?
Far Part 43 Appendix E and F
Altimeter testing is required when?
Anytime the static system is opened or closed except for the use of drains or alternate static source
Who can perform altimeter testing?
A certified mechanic with an airframe rating
Static test shall comply with…
FAR 43 appendix E
What instrument is required on all certified aircraft, except free balloons?
Airspeed Indicator
What does the Airspeed Indicator actually measure?
Differential pressure between the inside of a diaphragm and the instrument case
What is indicated airspeed?
the airspeed indicated on the instrument
What is calibrated airspeed?
Indicated airspeed correct for instrument and sensor position error
What is true airspeed?
Calibrated airspeed corrected for altitude (pressure) and temperature
What is the white arc on an altimeter?
is the flap operating range. The lower limit is the stalling speed at maximum weight with the gear and flaps fully extended (Vs) and the upper limit at the flaps extended speed (Vfe).
What is the blue radial line on the altimeter?
Multi-engine aircraft, indicates the best rate-of-climb with one engine inoperative (Vyse) and a red radial line indicates the one engine inoperative minimum control speed (Vmc).
What is required for aircraft that fly near the speed of sound?
A Machmeter
What is the Vertical Speed Indicator (VSI/IVSI)?
Provides the pilot with the rate the aircraft is climbing or descending
How is level flight maintained?
keeping the VSI pointer at 0
