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Pressure altitude to Indicated Altitude
Pressure altitude is taken from the 1013hPa datum. Indicated altitude is taken from the given QNH.
To convert PA to IA, calculate the difference between 1013hPa and the QNH and multiply by 30 (sometimes the Question will give you the value). Now you have the difference in feet between PA and IA.
Indicated altitude to True Altitude
True altitude takes into account the actual conditions, not just standard ISA. This means that there is a difference between the altitude you see Indicated on the instrument and the actual altitude flying (when not in ISA conditions).
The difference between IA and TA is the TEC (temperature error correction)
TEC = 4 x height AGL (/1000) x ISA Dev
4 = a constant
Height AGL (/1000) = The TEC takes the height above ground level into account, so subtract from the QNH the elevation and then divide by 1000
ISA Dev = Difference between ISA temperature at your altitude and the actual OAT
Fill in the values and you'll get the TEC in feet:
Important! Although we use the height AGL in the calculation, the actual end value needs to be subtracted from or added to the INDICATED ALTITUDE!
Pressure altitude and Density altitude
To convert PA into DA, calculate the ISA deviation.
Every 1° ISA Dev = 120ft
Pressure altitude is taken from the 1013hPa datum. Indicated altitude is taken from the given QNH.
To convert PA to IA, calculate the difference between 1013hPa and the QNH and multiply by 30 (sometimes the Question will give you the value). Now you have the difference in feet between PA and IA.
When QNH > 1013 , the Indicated altitude = higher than Pressure Altitude
When QNH < 1013 , the Indicated altitude = lower than Pressure Altitude
Indicated altitude to True Altitude
True altitude takes into account the actual conditions, not just standard ISA. This means that there is a difference between the altitude you see Indicated on the instrument and the actual altitude flying (when not in ISA conditions).
The difference between IA and TA is the TEC (temperature error correction)
TEC = 4 x height AGL (/1000) x ISA Dev
4 = a constant
Height AGL (/1000) = The TEC takes the height above ground level into account, so subtract from the QNH the elevation and then divide by 1000
ISA Dev = Difference between ISA temperature at your altitude and the actual OAT
Fill in the values and you'll get the TEC in feet:
When the OAT > ISA , True altitude = higher than Indicated altitude
When the OAT < ISA , True altitude = lower than Indicated altitude
Important! Although we use the height AGL in the calculation, the actual end value needs to be subtracted from or added to the INDICATED ALTITUDE!
Pressure altitude and Density altitude
To convert PA into DA, calculate the ISA deviation.
Every 1° ISA Dev = 120ft
When the OAT > ISA , Density altitude = higher than Pressure altitude
When the OAT < ISA , Density altitude = lower than Pressure altitude
