Commercial airline pilots are now becoming more and more dependent on their iPads, more specifically weather apps.  In fact, aerospace supplier Honeywell has come up with one called Weather Information Service.  It's a standalone subscription using on-board data connections to provide real-time rain, clouds, and turbulence forecasts in addition to current weather information.  

Weather Information Service collects data from a worldwide network of national weather sources.  Honeywell wouldn't disclose costs but said it varies depending on how many pilots use the software as well as other products the particular airline buys from Honeywell. 

This app also plugs into systems used by dispatchers.  They can push alerts to pilots, notifying them of significant weather and what should be done about it.

The app doesn't display the current location of the airplane, and the map doesn't move to follow the plane as it flies.  If it did, there would be the risk incorrect information could appear, prompting government oversight.  Honeywell does plan to update the app a few times a year. 

Meantime, Apple and IBM have built an iPad app called Plan Flight.  it lets commercial pilots estimate fuel usage for upcoming flights.