3GPP 24.501 v20.0.0 — the document's own text
5.5.1.3.6B Mobility and periodic registration update when an emergency services fallback is pending
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
If the registration procedure for mobility and periodic registration update was initiated neither for performing an emergency services fallback nor for establishing an emergency PDU session, there is a request from the upper layers to perform "emergency services fallback" pending, and the mobility and periodic registration update is not successfully completed, the UE may abort the registration procedure for mobility and periodic registration update, stop timer T3510, locally release the NAS signalling connection and behave as the mobility and periodic registration update request for an emergency fallback not accepted by the network as in clause 5.5.1.3.6A.