Airworthiness directives › 2021-11-04
AD 2021-11-04 Airworthiness Directives; De Havilland Aircraft of Canada Limited (Type Certificate Previously Held by Bombardier, Inc.) Airplanes
Models named: DHC-8-400, -401, -402. Read the applicability below — it usually turns on serial or part numbers too.
Applicability*9
This AD applies to De Havilland Aircraft of Canada Limited (type certificate previously held by Bombardier, Inc.) Model DHC-8-400, -401, and -402 airplanes, certificated in any category, having serial numbers 4001, and 4003 through 4534 inclusive.
Compliance
Comply with this AD within the compliance times specified, unless already done.
Required actions
Within 9 months after the effective date of this AD: Verify both the height of the lock link over-center stop pin and the gap of the left-hand and right-hand MLG downlock proximity sensors, and perform corrective actions as required, in accordance with paragraphs 3.A. and 3.B. of the Accomplishment Instructions of Bombardier Service Bulletin 84-32-140, Revision B, dated January 30, 2018. Do all applicable corrective actions before further flight.
Unsafe condition
This AD was prompted by a report of main landing gear (MLG) retractions after striking an obstacle or severe wheel imbalance after a tire failure. The FAA is issuing this AD to address loss of MLG downlock signal caused by the vibrations from those events, which leads to de-energizing the MLG solenoid sequence valve and subsequent removal of hydraulic pressure from the MLG downlock actuator. Loss of the hydraulic pressure in the downlock actuator, combined with the vibrations, can cause the stabilizer brace to unlock and the MLG to subsequently retract.
Affected ADs
None.
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The directive text above is reproduced from the Federal Register, a work of the United States government and in the public domain. The separation into applicability, compliance and required actions is TrackAD's.*1