The temperature you need to enter into the temperature error correction (TEC) is the ISA deviation. If this is presented as an ISA Deviation in the question, there is no further conversion required. But if it is presented as an OAT you need to identify the location from the question by using some reasoning. If the question said the aircraft was at FL 320 and the OAT is -48°C, logic states that is to be taken at the aircraft's altitude, especially if the aerodrome is at or closely sea level. If, on the other hand, the question said "the aircraft is at FL 330 and the QNH at an aerodrome 2850 ft amsl (OAT +18°C) is...." then logic states that's the temperature at the aerodrome - it's not going to be +18°C at FL330. Therefore, you calculate the ISA deviation at the aerodrome and add that to the TEC formula. Hope that helps. 🙂
Because you are only concerting between true and indicated altitudes, both of which are measured from sea level (QNH). There is no flight level, therefore no pressure altitude, therefore no pressure correction. If the question had asked for the lowest flight level, you would have needed QNH to convert indicated altitude to pressure altitude. OAT is provided as an ISA deviation so that is valid at all altitudes, so again no need to convert the met station from an elevation amsl to a pressure altitude. Hope that helps. QNH is there just to test your knowledge - do you know to ignore it?
In this question, you are calculating an indicated altitude amsl from a true altitude amsl. Both are measured from the same pressure datum, i.e. QNH. The only correction between indicated and true altitudes is TEMPERATURE CORRECTION. PRESSURE CORRECTION is applied between Pressure Altitude (from 1013 hPa) and Indicated Altitude (from QNH). REMEMBER P (P) I (T) T - Pressure Altitude (Pressure Correction) Indicated Altitude amsl (Temperature Correction) True Altitude amsl. Hope that helps.
Calculate the temperature error correction - * Negative ISA deviation = negative TEC * Positive ISA deviation = Positive TEC * If working from indicated altitude amsl to true altitude amsl, you apply it in the correct sense * If working from true altitude amsl to indicated altitude amsl, you apply it in the opposite sense If you use this formula, and transpose it as required, it should solve the problem for you: TRUE ALTITUDE = Indicated Altitude +/- TEC
The Formula you have to remember is TRUE ALTITUDE = INDICATED ALTITUDE + or - ISA DEVIATION. If the question asks for the True Altitude, then you would indeed add the 112 to the Indicated Altitude. Since you already know your True Altitude (9800 + 2000) you have to calculate back to the Indicated Alt., thus subtracting it in stead of adding it.
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The temperature you need to enter into the temperature error correction (TEC) is the ISA deviation.
If this is presented as an ISA Deviation in the question, there is no further conversion required. But if it is presented as an OAT you need to identify the location from the question by using some reasoning.
If the question said the aircraft was at FL 320 and the OAT is -48°C, logic states that is to be taken at the aircraft's altitude, especially if the aerodrome is at or closely sea level.
If, on the other hand, the question said "the aircraft is at FL 330 and the QNH at an aerodrome 2850 ft amsl (OAT +18°C) is...." then logic states that's the temperature at the aerodrome - it's not going to be +18°C at FL330. Therefore, you calculate the ISA deviation at the aerodrome and add that to the TEC formula.
Hope that helps. 🙂
Because you are only concerting between true and indicated altitudes, both of which are measured from sea level (QNH). There is no flight level, therefore no pressure altitude, therefore no pressure correction. If the question had asked for the lowest flight level, you would have needed QNH to convert indicated altitude to pressure altitude. OAT is provided as an ISA deviation so that is valid at all altitudes, so again no need to convert the met station from an elevation amsl to a pressure altitude. Hope that helps. QNH is there just to test your knowledge - do you know to ignore it?
In this question, you are calculating an indicated altitude amsl from a true altitude amsl. Both are measured from the same pressure datum, i.e. QNH. The only correction between indicated and true altitudes is TEMPERATURE CORRECTION.
PRESSURE CORRECTION is applied between Pressure Altitude (from 1013 hPa) and Indicated Altitude (from QNH).
REMEMBER P (P) I (T) T - Pressure Altitude (Pressure Correction) Indicated Altitude amsl (Temperature Correction) True Altitude amsl.
Hope that helps.
why don't you calculate for QNH correction?
Exactly what I was thinking.
so by OAT it mean temp at the airfield?
Super fantastic thanks a lot
Perfect explanation,awesome work,thanks a lot👌
Excellent work , Thank you
But why Pressure Correction is not done in order to find Indicated Altitude?
Calculate the temperature error correction -
* Negative ISA deviation = negative TEC
* Positive ISA deviation = Positive TEC
* If working from indicated altitude amsl to true altitude amsl, you apply it in the correct sense
* If working from true altitude amsl to indicated altitude amsl, you apply it in the opposite sense
If you use this formula, and transpose it as required, it should solve the problem for you:
TRUE ALTITUDE = Indicated Altitude +/- TEC
Pressure Altitude 8000 ft
QNH Altitude 7500 ft
OAT + 30° C
Terrain elevation 5700 ft
The approximate absolute altitude is?
8184 ft ?
why is the QNH irrelevant here?
Excellent explanation.. Thank you..!
Thank goodness for GPS (for cross-checking)!
Really helpful video! thanks!
why is it plus 112 and not minus. /how do you know which to use?
The Formula you have to remember is TRUE ALTITUDE = INDICATED ALTITUDE + or - ISA DEVIATION. If the question asks for the True Altitude, then you would indeed add the 112 to the Indicated Altitude. Since you already know your True Altitude (9800 + 2000) you have to calculate back to the Indicated Alt., thus subtracting it in stead of adding it.
Thanks