You know when you fly you have to either turn your phone off or put it on airplane mode, but did you ever think about why? pose a crash threat to some models of Boeing 737 and 777 airplanes. More than 1,300 jets registered in the U.S. had cockpit screens that were vulnerable to interference from WiFi, mobile phones, and even outside frequencies like weather radar. The Federal Aviation Administration (FAA) gave airlines until November 2019 to replace these units, and today, potentially hundreds of planes worldwide are still flying with the unsafe systems. The maker of the system—Honeywell—claims it hasn’t heard of any blanking of display screens caused by cell phones or other radio frequencies while the airplane was in flight, and the company and airlines argued that radio signals were unlikely to cause safety problems during flight. The FAA ran tests, however, and the jets flunked. Affected 737s are the so-called Next Generation model, and the other affected model are Boeing’s 777s. There have also been reports from numerous pilots since 2017 who have reported losing various flight information while in flight on the Honeywell displays.