AD 91-26-05 R1
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | The Boeing Company | 747-400 Series | Airworthiness Directives; BOEING Model 747-400 Series Airplanes |
| aircraft | The Boeing Company | 747-400D Series | Airworthiness Directives; BOEING Model 747-400 Series Airplanes |
Unsafe Condition
Loss of all very high frequency (VHF) radio voice communication transmission capability due to the audio management unit (AMU) with Boeing part numbers S220U000-101, -102, or -104 (Hughes-Avicom part numbers 1167014-140, -141, or -142).
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Within 14 days after December 30, 1991, add the AFM limitation stating the right VHF radio must be operational for dispatch. Replace the AMU with part number S220U000-105 (Hughes 1167014-143) per Boeing SB 747-23-2321 to terminate AD requirements. Ensure AMUs with the affected part numbers are not installed unless paragraph (a) is complied with.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
Within 14 days after December 30, 1991
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Boeing Model 747-400 Series airplanes excluding production line numbers 816, 839, and 961 and subsequent
AI-generated summary from the source AD text. Verify against the official source before acting.
Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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