AD 2021-11-04
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Bombardier | Various | Airworthiness Directives; De Havilland Aircraft of Canada Limited (Type Certificate Previously Held by Bombardier, Inc.) Airplanes |
| aircraft | Bombardier | Various | Airworthiness Directives; De Havilland Aircraft of Canada Limited (Type Certificate Previously Held by Bombardier, Inc.) Airplanes |
| aircraft | de Havilland | Aircraft of Canada Limited Model DHC-8-400 | Airworthiness Directives; De Havilland Aircraft of Canada Limited (Type Certificate Previously Held by Bombardier, Inc.) Airplanes |
Unsafe Condition
Loss of MLG downlock signal caused by vibrations from striking an obstacle or severe wheel imbalance after a tire failure, leading to de-energizing the MLG solenoid sequence valve and subsequent removal of hydraulic pressure from the MLG downlock actuator.
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Required Actions
Inspect for correct height of the lock link over-center stop pin and for correct gaps of the left-hand and right-hand MLG downlock proximity sensors, replace the shim if necessary, and install a new, improved proximity sensor electronic unit (PSEU) with software changes.
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Compliance Time
Within 50 flight hours
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Affected Aircraft
De Havilland Aircraft of Canada Limited Model DHC-8-400, -401, and -402 airplanes.
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Source: Official FAA Source ↗
Retrieved: Apr 6, 2026
Rights: U.S. Government Public Domain
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