It sounds like your external drive is being improperly ejected whenever your MacBook Air goes to sleep, which can potentially damage the drive. Here are a few suggestions to help with this issue:
1. Prevent Sleep Mode: One way to avoid this problem is to prevent your MacBook from going to sleep when the external drive is connected. You can adjust your Energy Saver settings in System Preferences to keep your MacBook awake.
2. Eject Drive Before Sleep: Make it a habit to manually eject your external drive before your MacBook goes to sleep. This can help prevent improper ejections.
3. Use Terminal Command: You can use a Terminal command to prevent your MacBook from sleeping while the external drive is connected. Open Terminal and type "sudo pmset -a sleep 0" to disable sleep mode, but remember to re-enable it later by using "sudo pmset -a sleep 1".
4. Update macOS: Ensure that your macOS is up to date. Sometimes, updates include fixes for issues like this.
5. Third-Party Software: There are third-party applications available that can help manage sleep settings and prevent issues with external drives. Apps like "Keep Drive Spinning" can keep your external drive active to avoid improper ejections.
6. Contact Apple Support: If none of these solutions work, it might be best to contact Apple Support for further assistance.
Hopefully, one of these suggestions helps resolve the issue with your external drive.