Altimeter Flashcards
How does an altimeter work?
- The altimeter is connected to the static port.
- There is a small bellows inside that is set to 29.92 at the factory and sealed (you can change it to your airport’s current altimeter setting)
- As you climb or descend, the bellows expands/contracts, giving you a reading on the instrument face
Altimeter Errors:
What conditions can cause your altimeter to read incorrectly?
Due to changes in the actual atmosphere and the standard, the following things can lead to errors in the Altimeter indication:
- Low pressure Systems
- Temperature variations
- Mountain effect and waves
- Abnormally high pressure
What does “From high to low, look out below” mean?
If you are flying from an area of high pressure to an area of low pressure, and did not correct your altimeter setting en-route, the altimeter will tell you that you are higher than you actually are.
This could lead you to think you are clearing towers or obstacles that you will actually hit
**The opposite is true. If you are flying from a low to a high, it will show that you are lower than you actually are
Abnormally high pressure that is cause by extremely cold and dry air masses can produce pressures above 31.00”. What is the procedure for these situations, given then most Altimeters can’t be set to higher than 31.00?
- ATC will issue the actual altimeter setting and confirm with pilots that they have 31.00 set on their altimeter.
- Altimeters of all IFR, VFR, and CVFR aircraft are to be set to 31.00” for enroute operations below 1800 ASL when the altimeter setting exceeds 31.00
When correcting for temperature to find your True/Absolute Altitude, you only have to calculate…
AGL distances.
Aerodrome height is always given in ASL. Then they will either give you altitude in ASL also or in AGL. If they also give it in ASL, only count up from the airport elevation, not up from sea level, cause that doesn’t make any sense.
What are the 5 altitudes?
- Indicated Altitude
- Pressure Altitude
- True Altitude
- Absolute Altitude
- Density Altitude
What is Pressure Altitude?
The altitude that is indicated when the altimerter is set to 29.92. It is the standard altitude corrected for non-standard atmospheric pressure and is used to find:
- True Altitude
- Density Altitude
- True Airspeed
How do you calculate Pressure Altitude?
- Subtract the current altimeter setting from 29.92
- Then multiply it by 1000
- Then add or subtract the answer from the elevation of the airport (or whatever altitude you need it for)
What is True Altitude?
This is our exact height above sea level
Heights on maps/charts are given in terms of true altitudes (their height above sea level)
True Altitude can be calculated on the E6B
What is Absolute Altitude?
The actual height above the surface of the earth(AGL), with the the altimeter correctly set, and non-standard variations in temperature accounted for
This is the True Altitude (exact height above SL), subtracting out the height of the terrain below. This is important on cross countries because it tells us how high we are above the terrain.
Are heights on maps given in AGL or ASL?
ASL
What is density altitude?
The altitude that our AC thinks its flying at. Pressure altitude corrected for temperature.
Calculated on the E6B and used for takeoff/climb charts
What is an Encoding Altimeter?
A Mode C Transponder. Allows ATC to know the pressure altitude as well as the position of a transponder equipped AC
