03 Altimeter Flashcards
Describe how an Altimeter operates;
- What feeds it
- Components
- How it operates
- Fed by a Static Pressure source into the sealed case
- Aneroid then expands or contracts accordingly turning the dial
- Can be adjusted by setting the sub scale
If an aerodrome is hilly or uneven what type of QFE will be issued?
Touchdown QFE
What are the errors an Altimeter suffers from?
- Instrument
- Manoeuvre
- Position
- Temperature
- Barometric
- Time Lag
How is the Barometric correction calculated for an Altimeter reading?
Difference between the ‘old’ sub scale setting and the ‘new’ sub scale setting multiplied by the altitude change per hpa value.
This is then added or subtracted from the original altitude given.
How is the temperature correction calculated for an Altimeter reading?
Either by:
- 4% per 10 degrees ISA deviation
- 4 x indicated altitude (divided by 1000) x ISA deviation
What happens if the Static Pressure feed for an Altimeter becomes blocked?
The static pressure in the case will not change and so the indicated altitude will not change
What happens if there is a leak in the Static Pressure feed of an Altimeter INSIDE a pressurised cabin?
The altimeter will under read due to the relatively higher pressure in the cabin compared to outside
What happens if there is a leak in the Static Pressure feed of an Altimeter OUTSIDE a pressurised cabin?
The altimeter will continue to read but at a loss of accuracy
What happens if there is a leak in the Static Pressure feed of an Altimeter INSIDE a non-pressurised cabin?
The altimeter will over read due to the reduced pressure in the cabin, caused by cabin suction
Describe the three types of Altimeter
- Simple: basic design, no sub scale setting, single layered aneroid
- Accurate: more accurate design, sub scale setting, multi-layered aneroid, vibrator to reduce Instrument error
- Servo: even more accurate design (even at high altitude), E and I beam design to remove Lag error
How is the density altitude correction calculated?
120 feet per 1 degree deviation from ISA
The Hysteresis error associated to an Altimeter varies with what?
- The Hysteresis of the Aneroid varies with temperature
- The amount of time spent at a specific altitude (and hence temperature) will vary the amount of Hysteresis error
What is the Density altitude?
Density Altitude is the altitude in the standard atmosphere where the given density is equal to the actual density
The Position error associated with an Altimeter varies with what?
The speed of the AC
The static pressure error on an Altimeter varies with?
- Mach Number (or TAS)
- Angle of Attack
