Though some countries are softening rules about using airplane mode during flights, it's best to comply with crew member directions and use airplane mode when you're instructed to. If you’ve ever wondered why your phone has to be in airplane mode during a flight, you’re not alone. In fact, many frequent fliers can’t recite the reasons behind the rule, and others have likely forgotten to turn it on at all. So, what really happens when you don’t use airplane mode? It depends on who you ask.  “Not a darn thing,” says Gary Coxe , a pilot and flight instructor with over 7,000 flight hours, including time spent piloting jets, helicopters, and gliders. A Washington-based airline mechanic who wishes to remain anonymous tells Travel + Leisure he agrees with Coxe’s sentiments.…