Final answer:
When deviating from an ATC clearance, one must contact ATC as soon as possible to explain the deviation for safety and to obtain further instructions. This communication ensures the pilot is following a path that maintains airspace safety and prevents conflicts with other aircraft.
Step-by-step explanation:
When deviating from an ATC clearance, the correct action to take is to contact ATC as soon as possible to explain the deviation. This is essential to ensure safety and to maintain separation from other aircraft. Not only does communication with ATC keep airspace organized, it also helps to prevent potential collisions. Once in contact, you may be given a new clearance that accommodates your deviation while still keeping you integrated into the traffic flow.
It is not advised to continue with the deviation without informing ATC, as this can lead to serious safety risks. Also, the deviation procedure outlined in the aircraft's operating manual is meant to guide the pilot on how to handle the aircraft during the deviation, but it does not replace the need for clearance or communication with ATC. So the third option - contacting ATC as soon as possible to explain the deviation - is the most appropriate course of action.