• Mean sea level pressure is 1013.25 hPa (hectopascals).
• The lapse rate of temperature is 6.5°C per kilometer (or 1.98°F per 1000 feet) between Mean Sea Level (MSL) and 11,000 meters (or 36,089 feet).
• The temperature is isothermal up to 11,000 meters (36,089 feet), meaning the temperature remains constant at 15°C.
• After 11,000 meters: Above this altitude, the temperature stops decreasing and remains constant at -56.5°C up to 20,000 meters (65,616 feet). This layer is known as the stratosphere and is still considered isothermal in this region.

• If the static vents are blocked by ice or another obstruction, the altimeter will read the altitude at which the vents were blocked, which in  will be the ground level IN THIS CASE
• As the aircraft climbs, the altimeter will not change and will give a false reading, remaining at the altitude where the vents were blocked.

• In simple terms: The altimeter assumes the aircraft is at a lower altitude (based on the lower pressure) than it really is, leading it to indicate a higher altitude than the actual one.
• Moving from low pressure to high pressure = altimeter shows a higher altitude than the actual altitude.
• Pilots must always ensure that they correct the altimeter setting when crossing into different pressure zones to ensure accurate altitude readings.

REMEMBER  LOW – HIGH- LOW

• Blockage: Altimeter freezes at the altitude where the blockage occurs.
• Leakage: The altimeter shows inaccurate readings, either too high or too low.
• Instrument Error: Malfunctions or poor calibration lead to incorrect altitude readings.
• Position Error: Static vent placement causes discrepancies in pressure readings.
• Temperature Error: Non-standard temperature causes the altimeter to over-read or under-read.
• Barometric Errors: Incorrect QNH setting or pressure changes cause the altimeter to indicate incorrect altitude.

REMEMBER BLIP TB

QNH: This setting on the altimeter will give the aircraft’s altitude above mean sea level (MSL).

Pressure Altitude (1013 hPa): When the altimeter is set to 1013 hPa (standard atmospheric pressure), it calculates the pressure altitude, which is the altitude corresponding to the standard atmospheric pressure at sea level (1013.25 hPa).

An aircraft has one altimeter set to QFE and one to aerodrome QNH 1000 mb. If the airfield elevation is 300 ft, immediately before take-off the altimeter with QFE set will read 0 ft (height above the airfield), and the other with QNH set will read 300 ft (the airfield elevation). If the QFE altimeter is set to 1013 hPa when passing through the transition altitude of 3000 ft, it will read 3300 ft.

Explanation:

• QFE Altimeter: The altimeter set to QFE reads the height above the airfield. So, immediately before takeoff, it will read 0 ft because the aircraft is at the airfield’s elevation.
• QNH Altimeter: The altimeter set to QNH will read the altitude above mean sea level (MSL). Since the airfield elevation is 300 ft, the altimeter will read 300 ft.
• When the QFE altimeter is set to 1013 hPa at the transition altitude, it will show the pressure altitude, adjusted for the airfield elevation.
  1. Airfield Elevation: 300 ft
  2. QNH (Aerodrome Pressure): 1000 hPa (local pressure at the airfield)
  3. QFE Altimeter: Set to 1013 hPa (standard pressure)

  Pressure Difference:

  • The pressure difference between QNH (1000 hPa) and 1013 hPa is 13 hPa (1013 – 1000 = 13 hPa).
  • The pressure difference of 1 hPa typically corresponds to a change of approximately 30 feet in altitude.

  So, for a 13 hPa difference, the altimeter reading will be adjusted by 13 * 30 feet, which equals 390 feet.

  Altimeter Reading at Transition Altitude:

  • The transition altitude is 3000 ft, but since the airfield is at 300 ft, you need to add the 390 feet correction due to the pressure difference.

  Therefore, the QFE altimeter, when set to 1013 hPa at transition altitude, will read:

  • 3000 ft 390 ft = 3390 ft.

IN ANALOG ALTIMETER THE SAMLEST NEEDLE IS THE MIGHTY ONE

THE SMALLEST NEEDLE POINTS AT 15

BIGGER ONE THAN IT POINTS AT 5

AND THE BIGGEST ONE AT 5

ALSO QNH SET IS 1013

Interpretation of the Needles:

1. Smallest Needle (indicating thousands): Points at 15 — This suggests the altitude is around 15,000 feet.
2. Bigger Needle (indicating hundreds): Points at 5 — This suggests the altitude is in the 500-foot range.
3. Biggest Needle (indicating tens): Points at 5 — This suggests the altitude is in the 50-foot range.

So, the combined reading of the altimeter would indicate an altitude of approximately 15,550 feet.

To summarize:

• Smallest Needle at 15 = 15,000 feet
• Bigger Needle at 5 = 500 feet
• Biggest Needle at 5 = 50 feet

Total Altitude = 15,550 feet.

1. Part A – Mechanical Drive:
   • Description: This component is responsible for transmitting the mechanical movement of the needle in the altimeter.
   • Function: It takes the output from the servo motor or pressure changes and moves the altimeter dial accordingly. The mechanical drive usually includes gears or springs and helps rotate the needles to show the altitude.
2. Part B – Servo Motor:
   • Description: The servo motor is a critical component in the servo-assisted altimeter system.
   • Function: It is used to position the mechanical drive. The servo motor responds to the control signals (often coming from an amplifier or sensor) to move the needle or display. It ensures accurate needle positioning based on changes in pressure (altitude).
3. Part C – Amplifier:
   • Description: The amplifier amplifies the signals coming from the pressure sensors or other control elements.
   • Function: The amplifier boosts the weak signals from the sensors to a level that can be used to drive the servo motor or other electronic components. In a servo-assisted altimeter, it ensures that the motor gets the correct input signal to move the needle accurately.
4. Part D – AC Exciter:
   • Description: The AC exciter provides an alternating current (AC) supply.
   • Function: In some altimeter designs, an AC exciter is used to power the electromagnetic systems, such as the gyro or servo motors. It supplies the necessary electrical energy to maintain system operation and stability.

Schematic Diagram Overview:

• The AC exciter (D) provides the power needed to operate the system.
• The amplifier (C) amplifies signals to ensure proper motor operation.
• The servo motor (B) moves the altimeter’s mechanical drive (A) in response to the amplified signals, which adjusts the needle or display to indicate the correct altitude.

In summary, the components work together to convert atmospheric pressure changes into mechanical movement (altimeter readings), with the servo motor being the key element in driving the mechanical system accurately.

Let me know if you’d like further details on how these components interact in specific altimeter models!