What does a 'CT' clearance signify?

A 'CT' clearance signifies that an aircraft is cleared for a contact approach. This type of approach allows pilots to navigate visually to the airport once they have established visual reference with the ground. The primary purpose of a contact approach is to expedite the arrival of an aircraft under specific conditions and in situations where there is sufficient visibility for the pilots to safely execute the approach without relying solely on instrument guidance.

In a contact approach, the pilot must be able to see the airport or the surrounding area to proceed safely to landing. This method enhances operational flexibility and helps maintain traffic flow, particularly in busy airspace. Pilots must request a contact approach, and air traffic controllers will provide the necessary clearances based on existing weather conditions and traffic scenarios.

Other options mention clearances like takeoff clearance or descent clearance, which are distinct functions in air traffic control and do not relate to the contact approach. Hence, 'CT' specifically and accurately aligns with the definition of a contact approach, which is why it is the correct answer.