Is it legal to fly without a transponder?
Yes, you can in the US in Class D, E &amp; G airspace according to 14 CFR 91.215. You will need to placard the transponder INOP, and make a note in the aircraft logbook. But, you must stay out of any Mode C Veils, and further than 30 miles from Class B airports. Also, stay below 10,000 feet MSL unless that means you are below 2,500 feet AGL. However, you can request a deviation to 91.215 from ATC in advance.