Team accountability is not easy, too often we ask teams to be accountable for working late to deliver things they have no control over and did not scope themselves. In my opinion, several conditions need to be in place for team to be fully accountable for deliverables.
The delivery of a task or iteration needs to have purpose or a clear goal, either business purpose, improving user experience or making financial sense.
The time allocated for the team to work on the tasks when committing to delivery timings does not change: either the team is full time on the project or the team context switching is kept at a minimum and project time ring-fenced.
Tasks being worked on are clearly defined from a business and user perspective and understood by all including stakeholders.
The whole team commits to deliverables, not separate individuals committing to separate tasks. The team has autonomy on deciding how the tasks are done and when each individual will get to work on them, i.e. each team member controls their daily workload and commit to a time as a team.
The project manager is there to help the team achieve what they committed to i.e. she is there to solve problems, remove obstacles, shield the team and negotiate with the stakeholders on their behalf, she is not just there to check if individuals are on target.
Only then you can have true team accountability.