🔍 Key Concepts

• DME (Distance Measuring Equipment) measures slant range by timing the trip of radio pulses between aircraft and ground station • There is a minimum time it physically takes for a radio signal to travel out and back, especially at very short distances • Consider why a deliberate delay in the ground station’s reply might be important when the aircraft is very close to the station

💭 Think About

• Think about what would happen to the measured distance if the ground station replied instantly when the aircraft was almost directly overhead • Which option is related to ensuring that the timing of the pulse travel represents a realistic, usable distance rather than effectively zero? • Which choices clearly have nothing to do with radio signal timing or distance measurement?

✅ Before You Answer

• Eliminate answers that deal with voice communication or human intervention, since DME is an automatic system • Ask whether the delay is about signal timing and minimum range rather than coordination with other equipment • Focus on the choice that would help make DME work properly when the aircraft is very close to the ground station