Apple’s new iOS 5 operating system is causing problems for iPad aviation app users, including deletion of data without warning and other glitches. In some cases, this can lead to deletion of files needed to display aeronautical charts on popular iPad apps such as ForeFlight and WingX.

The problem, according to a blog post from ForeFlight, is that apps that use large amounts of data store some of it in a cache directory, which iOS 5 can empty when it needs the space, instead of the documents directory, which doesn’t allow data to be deleted. ForeFlight checks for data when it is started and warns the user if missing data needs to be redownloaded.

WingX maker Hilton Software recommends waiting to upgrade to iOS 5 “until Apple’s iOS 5 stops deleting your apps and data.” Or, if already upgraded, “Keep several GB memory free to prevent random deletion of files.” Jeppesen’s Mobile FliteDeck app takes up only 1.5 GB for worldwide coverage. According to a Jeppesen spokesman, “We do not use the cache to store data so we are not subject to this data removal issue.” However, there are some “minor anomalies” with both Jeppesen Mobile TC and FD when using iOS5.