The U.S. Federal Aviation Administration (FAA) on Thursday issued fresh warnings that new 5G wireless service could still disrupt flights, saying there were “big differences” between U.S. aviation protections and those used in France.

Late Thursday, the FAA launched a dedicated webpage on 5G and aviation safety raising questions about potential impact on sensitive airplane electronics like altimeters.

This week, AT&T and Verizon agreed to adopt similar precautions to those in France. On Monday, the carriers said they would delay use of C-Band spectrum for wireless service until Jan. 19 — an agreement aimed at heading off an aviation safety crisis and flight disruptions.

On Tuesday, President Joe Biden hailed the deal between wireless carriers and U.S. regulators allowing 5G deployment in two weeks. The FAA said the delay would allow it to evaluate ways to minimize disruptions to altimeters, and also gives companies more time to prepare.

The FAA said 5G airport buffer zones in France cover “96 seconds of flight” while safety precautions around U.S. airports “only protect the last 20 seconds of flight.” It said temporary U.S. lower power levels will be 2.5 times higher than France. It noted that France requires antennas be tilted downward to limit harmful interference, a rule the United States lacks.