The finding of the court of trial or inquiry, as aforesaid, shall be of no effect until approved by the mayor, except in cases of conviction for intoxication while on duty in cities of the second class A; upon conviction of intoxication while on duty in such cities, the trial board shall immediately certify its findings to the mayor, who shall thereupon impose sentence on the convicted in the manner herein set forth.
53 P.S. § 30474