Electric, pneumatic and hydraulic drives have been in use for many years to facilitate the operation of landing gears on transport trailers. The following documents provide a good inventory of auxiliary, non-manual drive systems that have been found in the prior art for operating landing gears on transport trailers.    Canadian Patent 1,072,940 issued to Joseph P. Orth et al. on Mar. 4, 1980;    Canadian Patent 2,039,149 issued to R. P. Whittingham on Mar. 14, 1991;    Canadian Patent 2,339,156 issued to J. M. Alguera-Gallego et al. on Apr. 24, 2007;    Canadian Patent 2,531,272 issued to Frank J. Drake, on Mar. 16, 2010;    Canadian Patent Appl. 2,621,342 filed by Giancarlo Brun, on Aug. 14, 2006;    U.S. Pat. No. 2,875,980 issued to K. Grace on Mar. 3, 1959;    U.S. Pat. No. 3,077,120 issued to A. F. Viehweger, jr. on Feb. 12, 1963;    U.S. Pat. No. 3,189,322 issued to C. G. Hadek on Jun. 15, 1965;    U.S. Pat. No. 3,136,527 issued to L. Griffis on Jun. 9, 1964;    U.S. Pat. No. 3,341,179 issued to C. B. Smith on Sep. 12, 1967;    U.S. Pat. No. 4,097,840 issued to Warner A. Chappelle on Jun. 27, 1978;    U.S. Pat. No. 4,116,315 issued to Ervin K. Vandenberg on Sep. 26, 1978;    U.S. Pat. No. 4,129,322 issued to Martin Kuntz, Jr. on Dec. 12, 1978;    U.S. Pat. No. 4,281,852 issued to Raymond L. Konide on Aug. 4, 1981;    U.S. Pat. No. 4,466,637 issued to Carl A. Nelson on Aug. 21, 1984;    U.S. Pat. No. 5,299,829 issued to B. A. Rivers, Jr. et al., on Apr. 5, 1994;    U.S. Pat. No. 5,451,076 issued to Paul Burkhead on Sep. 19, 1995;    U.S. Pat. No. 6,224,103 issued to Edwin B. Hatcher on May 1, 2001;    U.S. Pat. No. 6,260,882 issued to Richard A. Kingsbury on Jul. 17, 2001;    U.S. Pat. No. 6,896,289 issued to Larry A. Gross on May 24, 2005;    U.S. Pat. No. 6,926,305 issued to Jeffrey Daniel on Aug. 9, 2005;    U.S. Pat. No. 7,163,207 issued to Darryl W. Baird et al. on Jan. 16, 2007;    U.S. Pat. No. 7,311,331 issued to Danny McGlothlin on Dec. 25, 2007;    U.S. Pat. No. 7,429,061 issued to John T. Perkins on Sep. 30, 2008.
Although all the power drive systems of the prior art deserve undeniable merits, these systems are not easily deactivated for use of a conventional hand crank in case of a malfunction of the power drive. In many installations in the prior art, the hand crank is no longer needed and is often stowed away and lost. It is believed that there is a need in the trucking industry for a better power drive system that is reliable, safe to operate, and that can be easily converted back to a manual operation when the need occurs.
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