Which of these is NOT a requirement for flight into Mexico?

Third-party insurance is not a requirement for flight into Mexico. While Mexico does have specific aviation regulations, the requirement for third-party insurance is generally not mandated for non-commercial flights. Instead, the emphasis is on having proper documentation and approvals, such as a valid radio operator certification, an IFR (Instrument Flight Rules) flight plan if operating under IFR, and notifying customs upon arrival.

In many cases, pilots flying into Mexico are well-advised to have insurance for liability protection, but it is not a legal requirement like the other listed items. Valid radio operator certification is necessary for communication purposes, an IFR flight plan is required for operating under instrument flight rules, and advising customs is crucial for compliance with regulatory entry procedures into the country.