The Federal Aviation Administration is investigating the emergency landing by a Mokulele Express plane last night on a Maui Highway.  The Cessna Caravan lost engine power after leaving Kahului Airport bound for Kamuela, on the Big Island.  The plane, with two pilots and eight passengers, landed safely on Piilani Highway, between Kilohana Drive and Okolani Drive in Wailea at about 7 p.m.  No one on the plane was injured. And, no one on the ground was injured, either.