This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
The <html:select> tag automatically looks at the existing value of the ActionForm property specified in the property attribute (tailno in your case) and highlights the values that match the values in the property. You're messing this up, though, by specifying value="0". Just remove the value attribute entirely and it should work.
Also, make sure there is a tailno property of type String in your ActionForm bean and that it's been populated prior to displaying the JSP.