Airwave is an appliance solution. The embedded database running on the appliance is not remotely accessible for backup solutions, and the internal backup should be used instead. It is not possible or supported to install third-party backup agents.
You can configure off-box backups via the CLI menu (console/SSH):
4) Backup
2) Configure Automatic Transfer
1) Set Destination
Backup Destination (user@host:path): user@scpserver:/backup/airwave/
Password:<password>
Also check the Airwave User Guide, Appendix B.