Well usually the difference between open source and proprietary is that the proprietary vendors are slow to fix security issues because it doesn't increase their profit. In some cases they even try to hide the fact that the software is insecure or even sue the person who reported the vulnerability. Meanwhile most OSS software gets fixed as soon as the vulnerability is found.

In the case of aircraft though a company could find a bug and do their best to fix it quickly. But if the plan is already flying any changes to the software require a re-certification of the software which can take months.