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Old 1st Jun 2023, 12:33
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MechEngr
 
Join Date: Oct 2019
Location: USA
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I suggested before that the QNH/runway barometric pressure be hashed by an aircraft computer for read back to the tower, preferably to an alphabetic code. This would require two separate values to be said and agreed upon to avoid errors due to swapped digits or misunderstood duplicated digits - 1023 vs 1032 and 1022 vs 1012. Getting the original value and the hash to have matching errors are infinitesimal and, with a properly designed hash, the hash could have only increasing values and never duplicate values.

1023 readback might be AD and 1032 might be AG,

It is important that the hash is not originally told by the tower to the plane; the tower sends pressure, the crew enters pressure, the computer generates hash, the crew respond to the tower with the hash, the tower reads back the hash and compares it to the hash they have. The goal is to prevent confirmation bias in parroting back what the crew thinks they hear and the tower hearing what they originally said.
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