3GPP aerial features are activated based on "aerial subscription" flag specified in Rel-15. This implies that an operator using these features will provide UAV users with USIMs that are associated to a user profile with the "aerial subscription" flag set. It is however technically possible for a UAV user to insert a USIM not meant for UAV in a UE that is on board a UAV (this UE being used for C2C or for other purpose). The user could do that either intentionally (e.g. to have a lower tariff or to bypass some restrictions applied to UAVs) or not (e.g. because he/she is not aware that UAVs need to be used with specific USIMs). In this case, with current specifications, the 3GPP network is not able to recognize that the UE is on board a UAV and therefore cannot activate aerial features. More importantly, the 3GPP network will not perform UAV Authentication and Authorization procedures with the UTM, and may cause the UE to use a frequency band that is not allowed for aerial usage where the UAV is located due to the risk of interference to users or adjacent frequency bands (e.g. military installation, weather radar). This has security implications. In addition, the 3GPP network cannot fulfill the requirements of TS 22.125 applicable to UE on board a UAV. From Rel-17 onwards, the 3GPP network is able to reject registration when the UE provides a "CAA-level UAV ID" and does not have the "aerial subscription" flag set in its subscription. This mitigates the above issue, but the issue still exists if the UE is pre-R17 or is not configured with a CAA-level UAV ID. There is therefore a need to enable the 5G System network to detect that a UE is on board a UAV, without relying on subscription information or on indication provided by the UE.

A UAV user has inserted in a UE on board a UAV, a USIM that is associated to a user profile without the "aerial subscription" flag set.

1. The UE registers in 5GS and starts communicating. The UAV takes off.
2. The network detects that the UE is on board a UAV.
3. The network takes action, e.g. activates aerial features, changes the QoS, populates charging records, alert the UTM and/or let the UTM take over the communication used to control the UAV.

The UTM may take over the communication used to control the UAV and force the UAV to land safely. Later, the UTM and/or network operator informs or reminds the user that a specific USIM needs to be used for proper operation of a UE on board a UAV.

• "aerial subscription" flag in subscription;
• Provision of "CAA-level UAV ID" by the UE;
• detection of UE above altitude thresholds by the eNB / gNB (per TS 36.331 & TS 38.331).

[PR 5.1.6-001]