the pilot explained the move had been executed becasue he was unsure if another aircraft was still climbing or had levelled out
Hi Darnicmax,
I'm guessing by this the pilot is referring to the combined rate of closure between the aircraft you were on and another aircraft and what his TCAS told him to do. As the TCAS system works on a time based rate of closure between aircraft (predicting a kind of "Time-to-go to collision"), it may have projected that there was going to be a conflict, hence the instruction to climb. The other aircraft would have (hopefully
) been cleared to an altitude 1000 feet (300 metres) below your flight, but if they were climbing at say 2000 feet per minute and the aircraft you were on was descending at 2000 feet per minute as well, you've got 4000 fpm closure. Depending upon how close the aircraft were, that certainly could be enough to generate what is known as a Resolution Advisory (RA), which is where the TCAS tells the pilot to climb (or descend).