AD 90-21-09
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | The Boeing Company | 747-100 Series | Airworthiness Directives; BOEING Model 747 Series Airplanes |
| aircraft | The Boeing Company | 747-100B Series | Airworthiness Directives; BOEING Model 747 Series Airplanes |
| aircraft | The Boeing Company | 747-100B SUD Series | Airworthiness Directives; BOEING Model 747 Series Airplanes |
| aircraft | The Boeing Company | 747-200B Series | Airworthiness Directives; BOEING Model 747 Series Airplanes |
| aircraft | The Boeing Company | 747-200C Series | Airworthiness Directives; BOEING Model 747 Series Airplanes |
| aircraft | The Boeing Company | 747-200F Series | Airworthiness Directives; BOEING Model 747 Series Airplanes |
| aircraft | The Boeing Company | 747-300 Series | Airworthiness Directives; BOEING Model 747 Series Airplanes |
| aircraft | The Boeing Company | 747SP Series | Airworthiness Directives; BOEING Model 747 Series Airplanes |
| aircraft | The Boeing Company | 747SR Series | Airworthiness Directives; BOEING Model 747 Series Airplanes |
Unsafe Condition
Failure of crossover pneumatic ducts could damage air conditioning packs, wing fairing panels, and/or electrical wiring.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Conduct a penetrant inspection, proof pressure test, and re-inspection to detect cracks or ruptures of crossover ducts per Boeing SB 747-36-2078 Rev 2. Repair or replace ducts if defects are found. Stress relieve ducts as part of the inspection process. Repeat inspections and stress relief within specified flight cycles after initial inspection. Full replacement of ducts per SB terminates AD requirements.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
Prior to the accumulation of 5,850 flight cycles, or within 4,000 flight cycles since last inspection and testing per SB 747-36-2078 Rev 1, or within the next 1,850 flight cycles after the AD's effective date (November 9, 1990), whichever occurs later. Subsequent actions under paragraph B must be done before 3,000 flight cycles after the initial inspection.
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Boeing Model 747 series airplanes except Model 747-400, line position 002 through 707, certificated in any category.
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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