When must an aircraft have an operable transponder?

An aircraft must have an operable transponder at and above 10,000 feet Mean Sea Level (MSL), excluding operations at or below 2,500 feet AGL. This requirement ensures that air traffic control can effectively track aircraft operating at higher altitudes, where the density of air traffic typically increases and the need for collision avoidance measures becomes more critical.

The regulation specifically excludes operations below 2,500 feet AGL because, in that altitude range, aircraft are often flying in visual flight rules (VFR) conditions, where direct visual separation and communication between pilots and air traffic controllers tend to be more common. Therefore, the transponder is not mandated in that lower altitude, allowing for greater flexibility for general aviation operations. However, once an aircraft ascends to 10,000 feet MSL, it becomes part of a more controlled airspace environment, necessitating the use of a transponder to maintain safety and enhance situational awareness.