Aviation Calculations & Conversions by Joachim K. Hochwarth

The following calculations have been carefully reviewed and tested but it cannot be guaranteed that they will return correct results! Please send any Comments/Suggestions/Questions to "aviationcalculator at hochwarth.com".

· Calculate QNH & QFE

· Calculate Crossover Altitude

· International Standard Atmosphere (ISA) & U.S. Standard Atmosphere of 1976

· Calculate Pressure Altitude

· CAS/Mach/TAS/EAS Conversions

· Great Circle Calculator (by Ed Williams)

QNH refers to the altimeter setting so that an aircraft's altitude above MSL (Mean Sea Level) is indicated. This setting is used during departure and approach and requires the pilot to set the local pressure at MSL. It is provided in the ATIS information and by ATC.

The Crossosver Altitude is the altitude at which a specified CAS and Mach value represent the same TAS value. The curves for constant CAS and constant Mach intersect at this point. The Mach number is used above this altitude to reference speeds.

The following calculations are based on the International Standard Atmosphere (ISA) & U.S. Standard Atmosphere of 1976. The current implementation will only give correct results for altitudes up to 32,000 [m] - i.e. Troposphere (Layer 0)/Tropopause (Layer 1) and Lower Stratosphere (Layer 2).

This will calculate the altitude at which the specified pressure can be found. It is the inverse calculation of the above International Standard Atmosphere (ISA) & U.S. Standard Atmosphere of 1976 pressure calculation and is subject to the same limitation of 32,000 [m].

The following will calculate three speeds based on the altitude and entered fourth speed - e.g. CAS/Mach/EAS based on Altitude and TAS. These calculations are based on the International Standard Atmosphere (ISA) & U.S. Standard Atmosphere of 1976 and are subject to the same 32,000 [m] limitation. They are also resticted to only subsonic speeds. The calculation is performed by pressing the button below the entered speed - e.g. TAS.

**1.8.6** (03/08/2023)

· The conversion from Mach to CAS now properly converts to [m/s].

**1.8.5** (10/08/2022)

· Speed Units now include [m/s].

**1.8.4** (06/06/2022)

· The site is now https:// instead of http://.

**1.8.3** (03/30/2018)

· The link to Great Circle Calculator (by Ed Williams) was updated.

**1.8.2** (05/10/2017)

· The site should again work with Edge and Internet Explorer 11.

**1.8.1** (04/02/2017)

· The site now issues a warning if JavaScript is not enabled.

**1.8.0** (01/02/2017)

· Calculations now include the Lower Stratosphere (20,000 - 32,000 [m]) while also referencing the International Standard Atmosphere (ISA) in addition to the U.S. Standard Atmosphere of 1976.

· CAS/Mach/TAS/EAS Conversions now include Delta International Standard Atmosphere (DISA).

· International Standard Atmosphere (ISA) & U.S. Standard Atmosphere of 1976 as well as Calculate Pressure Altitude will calculate on Enter.

**1.0.0 - 1.7.4**

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