Can anyone tell me why the FAA makes DME a requirement for flight s above 24,000 feet? Also, does anyone actually ever use VFR on top??? Just some questions that popped into my mind during my instrument ground. The instructor wasn't sure why DME is needed. His best thought was if you are not in radar coverage and ATC wants to know your location. He also said VFR on top is useless. I tend to agree.