In my humble opinion, when writing an episode for a sci/fi-drama series, there are three questions that must be asked regarding the script and plot of the episode...
1) Do the events in the episode advance the overall season arc in any way?
2) Do the events in the episode advance any character development in a significant way?
3) If a regular viewer were to miss this episode, would they be any worse for it?
Unless the answer to at least one of these questions is a resounding yes, then the episode is just a space filler.
In the case of turbulence, there were two main points of progression in the season arc. One, we found out that Chloe can apparently prevent the emergence of Doomsday in Davis, which will likely become significant towards the end of the season; and two, the trust issues that were never completely resolved between Chloe and Jimmy came to a head, with Jimmy leaving Chloe.
I found that in the past, some of the best episodes of the series were single plot episodes, with no split in the focus and pacing, or dual plot episodes where the multiples story lines come to a joint conclusion. This episode did not do that. It was a dual plot episode where the one story line had absolutely nothing to do with the other. The secondary plot line of Tess and Clark on the plane did not fulfill any of the three questions above, and could likely have been dropped from the episode with no major loss. This would also have allowed the writers to focus more on the trio, and develop the tension between Davis, Chloe and Jimmy a little further.
While some of the scenes with Clark and Tess were touching, and could be said to have character development for Tess, I have always felt that she is a bit of a superfluous character and we did not learn anything about her that we didn't already know, or that would be relevant to the remainder of the season. She generally just takes up time that could better be used elsewhere.
On a positive note, I find that the dialogue has been excellently written, and the producers/directors continue to produce music montages that bring tears to my eyes. The scene at the end with Jimmy leaving Chloe and the beginning of drug addition in Jimmy were heartbreaking, and the choice of song, (Apocalyptica's I Don't Care) was perfect. I am greatly looking forward to next week!