Fans of Dick Wolf's Chicago franchise are already well aware of the cast changes coming up this season (see: Sophia Bush's exit, Tracy Spiridakos' promotion and Jon Seda's return on P.D., and that potentially fatal finale cliffhanger on Fire).

However, there are also a few changes behind the scenes this season with the recent departures of Chicago Fire co-creator and co-showrunner Michael Brandt, Chicago P.D. co-creator and showrunner Matt Olmstead, Chicago Fire exec producer and director Joe Chappelle, and Chicago P.D. exec producer and director Mark Tinker.

"It's always sad to see people you work with, who you believe in, leave," Wolf Films president and Chicago Fire and Chicago P.D. exec producer Peter Jankowski tells The Hollywood Reporter.

Although the number of exits may seem to hint at a larger trend, Chicago Fire co-creator and showrunner Derek Haas insists "they were all under different circumstances."

Olmstead was the first to announce his exit in March. After four years as showrunner of Chicago P.D., three of which he also held same title on Chicago Fire, the former Prison Break executive producer left for a rich overall deal at ABC Studios in May.

Speaking with reporters at the Television Critics Association summer press tour in August, Wolf chalked Olmstead's departure up to exhaustion from his work across the Chicago universe. "With Matt, it was just a question of, he's kind of burned out. Everybody forgot that he was really on point for three shows. It's very hard," Wolf said, pointing to Olmstead's work launching spinoffs Chicago Med in 2015 and Chicago Justice in 2016, both as backdoor pilots.

Haas knows first-hand the challenge of juggling two shows. He and Brandt wrote for both Fire and P.D. during the latter's first three seasons before turning their attention Fire as co-showrunners. "I will say that I felt spread too thin at that point in terms of writing," Haas says of his three years juggling both shows. "It's a lot to bounce back and forth."

However, a year after taking over for Olmstead atop Fire, Brandt and Haas went their separate ways when Brandt quietly exited in May. The two had logged nearly 20 years as writing partners, penning such films as 2 Fast 2 Furious, 3:10 to Yuma and Wanted before they created Chicago Fire in 2011.

"We were talking a lot last year and right before Chicago Fire took off — and you don't know when you're doing these thing that this is going to be the next six years of your life — we had just done an independent movie [The Double] that he directed and he just loved directing and loved movies," Haas says. "The problem with being on a TV show is it takes all of your time and even directing, he would have to direct the finale because you have to get all of the writing done before. I just think he really was having the itch to direct more and I said to him, 'Go with God, no hard feelings on my end.' I love the writing part, I always have, I've never directed anything, so you go do your thing and I'll do this.'"

The season six premiere, titled "It Wasn't Enough" will mark Haas' first solo script on the franchise. "I've written six books by myself, so there was never a question of whether or not, in my mind, I could do it. I never had any concerns or doubts," he says. "I think people will enjoy [the episode]."

Following Brandt's departure, longtime series writers Michael Gilvary and Andrea Newman have been promoted to exec producers for season six. (They both also inked overall deals with Universal TV.) "[They] are just the most talented writers. I feel lucky that we've had them and they haven't gone off to do their own shows," Haas says of the duo, who have both been at Fire since season one. "It is awesome getting to write and do my own episodes, but I also have them to stand on their shoulders, so there's a comfort factor in that."

Wolf Films also looked to individuals with previous experience in the Chicago universe when it came time to fill the resident director slots open on Fire and P.D. "If the shows are managed correctly, there's a strong bench of people," Jankowski says.

Case in point? New Chicago Fire co-exec producer/director Reza Tabrizi, whose work dates back to the pilot of the drama. "Reza had already directed a dozen episodes for us and had been on the pilot as a camera operator and so he knows these characters so well," Haas says. "I'm so encouraged about all of it."

Tabrizi replaces Chappelle, who stepped away from the franchise to direct an indie film he also wrote called The Pages. "We said, 'Tell us as soon you're done with that, because we want you to direct Chicago Fire,' which he's going to do in the second half of the season," Haas says.

Chicago P.D.'s new resident exec producer/director, ER alum Eriq La Salle, had already helmed two episodes of the cop drama, as well as two episodes of Chicago Med and one installment of Chicago Justice, before coming on board full-time.

In addition to La Salle, P.D. has tapped Rick Eid to succeed Olmstead as showrunner. While new to the Chicago franchise, Eid has worked with Wolf Films several times before, first on Law & Order and most recently as showrunner of Law & Order: SVU last season. The Wolf Films team subsequently recruited another Law & Order vet, Michael Chernuchin, to take over on SVU after the other Wolf-produced series he was working on, Chicago Justice, failed to earn a second-season pickup.

"There was a need on P.D. to shake things up a bit, and it was natural move for us to bring Rick Eid over to P.D. and put Michael on SVU," Jankowski says. "It's playing into what the writers do best."

Despite Chernuchin landing at SVU, Jankowski is still upset about the surprise cancellation of Justice, the fourth spinoff in the Chicago franchise. "It was a sad day for us because I think we delivered a great show and it was a wonderful show to work on because of the people we had on it," says Jankowski, who adds that there has been no talk yet of any other offshoots. "I think we're still accepting the fact that that's not coming back."

The Chicago franchise will be down another series this fall because Chicago Med is being held for a midseason return. The 20-episode third season will move to Tuesdays at 10 p.m. once Law & Order True Crime wraps its eight-episode run. That was a result of NBC's sudden reversal in June not to move This Is Us to Thursdays as it had touted to advertisers at its annual upfront presentation in May. As a result, Chicago Fire will air Thursdays at 10 p.m. for the first time.

"Our challenge this year is making sure people know where the shows are," says Jankowski. The Universal Television veteran vividly remembers watching Murder, She Wrote plummet from No. 8 to No. 58 in the ratings when CBS moved the Angela Lansbury drama from Sundays to Thursdays. The move ultimately proved fatal and Murder was canceled in its 12th season.

"I learned from that, when you move a hit, you take a big risk," he recalls. "I think the television world has changed a lot since then with streaming and recording devices but it's still something to think about. NBC has been great. They've been getting the word out and we're trying to make shows a little noisier this year."

Thankfully, the changes at the various series have also made some noise. "Sophia's leaving P.D. and she was a big part of our show. How that affects viewership, I don't know. It also gives us something to play and reflect upon and have our characters react to so it does help creatively on a certain level," says Jankowski, who adds, "the show's better than ever."

Haas echoes that sentiment: "Dick Wolf has a standard that is, to me, the highest you can get on network television."

Chicago P.D. returns Sept. 27 at 10 p.m., followed by Chicago Fire on Sept. 28 at 10 p.m.