Ask HN: As a team lead how to handle project going off the rails?

You will never be thanked for telling them uncomfortable truths, even if they -don't- know. Even the private conversation is dangerous; as you say, keep it as low key and minimal as possible ("i have some concerns about the timeline" is literally all you should say unless they ask, and your answers to any followup question should be equally circumspect).

Instead, as others have mentioned, just make sure you document what does get done. Ideally have a decent backlog of things that need to get done, but that presumes a PO who does their job (and it sounds like he/she probably isn't). That's your CYA, and your innocent response if they ask why you didn't raise the alarm.

It's very tempting to think that on a practical level, people 'need to know' what's going wrong. Unfortunately it is often very difficult to accurately or objectively assess what the underlying problems are and in many cases, what you perceive as a problem can actually turn out to be a symptom of some other issue.

Project slippage happens all the time - and in and of itself it may not indicate any serious issues. It could just be a case of poor estimation, or scope creep, or some other 'process' related issue which is unlikely to be something any single individual can do anything about.

In my experience, the best way to deal with these kinds of situations is to make sure you're keeping your relevant colleagues up to date. If you feel like some deadline isn't going to be hit - it's probably best to voice your concern about that risk (and only that risk) to your immediate superior. In many cases it's likely that people are well aware of how behind things are - but everyone has a different assessment as to why.

In such situations it's often the case that the most you can do is to tend your own garden. It's important to keep the chain of command - even in small organisations (and especially when dealing with multiple teams / stakeholders), and avoid trying to assign blame (or even identify 'the cause') unless specifically tasked with figuring it out.

Basically: if it's not your job to raise hell about things, then don't. Keep your superiors up to date with progress and let them figure out the implications.

Although it can be intensely boring, project management tools can help to de-politicise these kinds of situations: graphs aren't personal, and the more regularly the relevant people can get a snapshot of progress, the less likely it is that it'll fall to you to point out when things aren't going as expected.

But of course, they still try it anyway.

Lead: "We're in serious danger of missing our delivery date in 6 months."

Suit: "Egads! Here, have 5 new grads with no experience for your team, get it done!"

“What happens if the deadline slips?”

If the project is late, does the company go out of business? Do people get fired? Is the overall deliverable unusable within the org? Is the deal lost?

If the answer to these is a big “no” then totally agreed with OP to not sound an alarm.

However configuring a skilled team and leading it to do excellent work and constantly improve should be something most people strive for.

At least, at my org, these are all considered appropriate.