Pinch zoom is not working on IOS devices?

Pinch zoom is a key feature of mobile browsing, which allow you to to zoom in to read content and out to locate content within a page. I am trying to enable this feature on my website. I've tried to enable zooming by setting meta viewport like this.
It's working on my android smartphone(Sony) but it's not zoomable on iPad and iPhone. My site www.pnrstatusbuzz.in is a php site, design in HTML5. Is this a designing issue or error in above mentioned code.