AD 56-17-02
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Viking Air Limited | DHC-3 | Airworthiness Directives; de Havilland Model DHC-3 Otter Aircraft |
Unsafe Condition
Malfunctioning of the flap hydraulic circuit check valve could fail to lock flaps in extended positions, leading to rapid flap retraction without pump use at high speeds, resulting in dangerous stick forces and out-of-trim conditions.
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Required Actions
Incorporate de Havilland Modifications 3/731, 3/744, and 3/745 by November 1, 1957, as outlined in D.H. Engineering Bulletin Series 'O' No. 34. Until modifications are done, restrict flap selector use: do not place flaps up until desired retraction and limit speeds based on flap settings (65 mph IAS for 35°, 75 mph for 30°, 85 mph for 15°).
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Compliance Time
by November 1, 1957
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Affected Aircraft
All Model DHC-3 Otter Aircraft manufactured by Viking Air Limited
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Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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