Final answer:
At tower-controlled airports, clearance must be obtained to cross each runway during taxi operations to ensure the safe movement of aircraft.
Step-by-step explanation:
When taxiing at a tower-controlled airport, it is indeed necessary to receive clearance to cross each runway during taxi operations. This is because runways are designated areas for aircraft takeoff and landing, and crossing them without proper authorization could lead to accidents or disruptions in the flow of air traffic.
Runway crossings are regulated by air traffic controllers who ensure the safe movement of aircraft on the ground. They provide clearance to pilots, specifying when and where they can cross a runway. This clearance is typically given after confirming that no other aircraft are approaching or using the runway.
For example, if a pilot is taxiing towards a runway and needs to cross it to reach their designated departure point, they will contact the tower and request permission to cross the runway. The air traffic controller will then assess the situation, check for any conflicting traffic, and grant clearance for the pilot to proceed.