Pinch zoom is not working on IOS devices?

Question

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.

<meta name="viewport" content="width=device-width,initial-scale=1">

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.