An A319 Captain called in fatigued prior to beginning the third trip in a six day sequence which switched sleep cycles from a red eye trip; to a day time sequence; then back to a red eye trip. The sleep cycle did not allow adequate rest.

Narrative

After flying my second red-eye; I felt it was going to be impossible to switch my sleep cycle a second time in just 4 days. So I decided to call scheduling immediately and inform them that I was Fatigued and would not be able to show back at the airport at 6 pm for my evening flight. I was never unable to perform my duties ever; but I do know if I had tried to fly the last pairing in this series my fatigue from changing sleep cycles would eventually increase the likelihood that I would make a mistake and not catch it. I have flown several red-eyes over several days; but the constant changes to my sleep cycle make it difficult to get a consistent amount of quality sleep. The reason I was fatigued and could not perform the last pairing on this 6 day stretch was because I had started 4 days earlier flying early morning flights. Then two days later I was scheduled for a 30 hour rest then I would start 2 days of red-eyes. Then on the last red-eye I was scheduled to have 12 hrs off and then report back to fly and early evening shift. After finishing the last red-eye I did not feel it was wise to try and change sleep cycles for a third time. Once I determined I was fatigued. I called scheduling and informed them I would not be able to report for my trip that afternoon. To avoid this from happening again. The company should not be allowed to change your sleep cycle from day to night and back to days without at least 24hrs off. This is not safe and it should not be done ever. If your going to fly red-eyes then fly red-eyes. They should not mix day and night flying.