Apple officially warned its users to update the older iPhone and iPad software to the latest available version prior to November 3, due to a risk of a nasty GPS bug. The warning concerns mainly the iPhone 5 and earlier as well as the iPad 4 and the earlier models. Depending on their generation, for some of these devices the update will be iOS 9.3.6, and for others iOS 10.3.4.
All devices which are not updated prior to the November 3 deadline can expect GPS location issues as well as some problems with keeping accurate date and time. At the same time, the latter could prevent Apple devices from fetching further updates over the air and sync with certain online services, such as iCloud and email servers. After November 3, an additional update via iTunes will be required to bring them back to normal operation.
Actually, the most interesting fact about the latest issue is that it is much bigger than Apple’s own domain and is capable of affecting almost every GPS-enabled device which has not been properly patched or prepared to handle what is essentially a GPS Y2K event.
In general, GPS systems count weeks using a ten-bit variable or register. Thus, values can only go from 0 to 1023 on the said counter. So, when a device hits week 1024, if not programmed correctly, it could restart or “rollover” the said counter in a way that corrupts it and makes it not usable for working with GPS and its precise timing data. In other words, the absolutely precise timekeeping is crucial for a GPS operation. In this case, why is this issue occurring now?
Well, the first GPS week counter was kicked off on January 6, 1980. After that, on August 21, 1999, the week counter got full for the first time and needed to be restarted. That was the end of the first “GPS epoch”. Counting forward, that puts the end of the second epoch on April 6, 2019. But before you say that April 6 passed quite a while ago, you’d better read the explanation below.
You should bear in mind that some manufacturers and software developers might have restarted their GPS week counters at a later time. For example, the GPS firmware was compiled and shipped to devices. Obviously, this was the case for Apple and that’s where their precise calculation and the November 3 deadline have come from.
In any case, it is a good idea for users of older iPhones or iPads to check the current status on their older GPS-enabled devices and see if they can be updated. Specialized devices, such as dedicated navigation units and in-car ones, are also included.