AD 2002-06-06
Unsafe Condition
Erroneous altitude reporting from Rockwell Collins TDR-94 and TDR-94D Mode S transponders when deriving altitude information from a Gillham (gray code) encoded pressure altitude source, which could lead to reduced ACAS or TCAS Change 7 separation margins.
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Required Actions
Modify the unit to prevent erroneous altitude reporting.
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Compliance Time
Before further flight.
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Affected Aircraft
Rockwell Collins TDR-94 and TDR-94D Mode S transponders installed on airplanes, specifically those deriving altitude information from a Gillham (gray code) encoded pressure altitude source.
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Source: Official FAA Source ↗
Retrieved: Apr 6, 2026
Rights: U.S. Government Public Domain
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