1 February 2000
Uncommanded Landing Gear Retractions
The following article was written by the FAA Aircraft Certification Office, ASW-150, in Fort Worth, Texas, and printed in the FAA's "ALERTS" publication, AC 43-16A, No. 256, November 1999.
Fairchild; Models SA226 and SA227; Metro; Landing Gear Anomaly; ATA 3230
"Two Metros recently experienced uncommanded landing gear retractions during ground operations. Both aircraft were equipped with the same Hydraulic Power Pack (P/N 27-81009).
In both cases, the cause was determined to be an undetected or latent malfunction within the landing gear control valve, which is a component of the Hydraulic Power Pack. As a result, the manufacturer (Fairchild) issued Service Letters (SL) 226-SL-012, 227-SL-037, and CC7-SL-029, with subsequent revisions, to establish overhaul criteria for the Hydraulic Power Pack and for system ground operating procedures.
The repetitive overhaul procedures required by the Service Letters will eliminate the latent failures that caused the uncommanded gear retractions. These failures are not necessarily detectable in the normal landing gear functional checks, and could occur at any time on high time Hydraulic Power Packs unless the preventive maintenance required by the Service Letter is performed. Although the reported malfunctions have thus far occurred with the affected aircraft in a ground static position, it is possible that such an uncommanded gear retraction could occur during an approach if electrical power to the Hydraulic Power Pack is interrupted."
In light of the preceding information, Transport Canada highly recommends that operators of SA226 and SA227 aircraft revise their approved Maintenance Schedules/Programs to incorporate hydraulic power pack overhauls in accordance with the recommendations stated in the latest revision of the above-mentioned Service Letters.
For further information contact a Transport Canada Centre, or call Mr. Mark Stephenson, Continuing Airworthiness, Ottawa, telephone (613) 952-4363, facsimile (613) 996-9178 or e-mail email@example.com.
For Director, National Aircraft Certification
Chief, Continuing Airworthiness