For operation temperature max above 25000 ft, what ISA deviation applies?

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Multiple Choice

For operation temperature max above 25000 ft, what ISA deviation applies?

At high altitude, performance data are based on ISA with a permitted positive deviation. For operations with a maximum altitude above 25,000 ft, the allowable ISA deviation is ISA plus 31 degrees Celsius. This means the actual ambient temperature can be up to 31°C warmer than the ISA temperature at that altitude and you’re still within the approved envelope. Remember that ISA deviation is defined as actual temperature minus ISA at that altitude. For example, if ISA at 30,000 ft is around −44°C, an ambient temperature of −13°C would be +31°C relative to ISA. If it were warmer than that, you’d be outside the allowable deviation and performance data may not apply. The other options don’t fit because this operational threshold uses a specific allowable positive deviation (+31°C) rather than standard ISA (0) or other arbitrary amounts.

At high altitude, performance data are based on ISA with a permitted positive deviation. For operations with a maximum altitude above 25,000 ft, the allowable ISA deviation is ISA plus 31 degrees Celsius. This means the actual ambient temperature can be up to 31°C warmer than the ISA temperature at that altitude and you’re still within the approved envelope.

Remember that ISA deviation is defined as actual temperature minus ISA at that altitude. For example, if ISA at 30,000 ft is around −44°C, an ambient temperature of −13°C would be +31°C relative to ISA. If it were warmer than that, you’d be outside the allowable deviation and performance data may not apply.

The other options don’t fit because this operational threshold uses a specific allowable positive deviation (+31°C) rather than standard ISA (0) or other arbitrary amounts.

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