Please configure your phones to forward emergency goal to PSTN gateway directly. You should use this feature, only if your phone does not support direct forwarding.
If this feature is enabled all emergency calls will be forwarded to default gateway. Optionally you can configure a set of phone numbers that will be forwarded to the alternative gateway.

Default settings

Use this feature only if phones do not support direct routing of emergency calls to PSTN gateways.

Forwarding Exceptions
Forwarding Exceptions