How to handle a situation where you are part of 2 competing projects? I am part of 2 collaborations which are more or less competing (in a friendly way though). Since I am the only one direct connection of these two groups (apart from the topic of course) that has now put me into a somewhat strange situation:

Both collaborations are about to submit a paper to an important journal in our area. In one of papers I am actively involved in the writing process, in the other I am actively involved in correcting what has been written by a collaborator. Particularly in this journal, I have the feeling that the paper which is submitted later might be rejected as being no longer the first one - although both papers are using different approaches to get to a similar result. (Of course, I might be wrong and everything goes through smoothly).

My question now: being part of both collaborations, can I tell the other collaboration that their colleagues/competitors are about to submit a paper where I am also involved ? Or would that be ethically not OK ?
Not sure if it applies to your field, but in some cases it is appropriate for researchers to publish simultaneously when they are working on something so similar at the same time (especially with a consistent finding but a different approach, like you suggest is the case here).

Some journals may consider the two papers side-by-side and publish them in sequence in the same issue, or they may be published in different journals. Typically there would be some acknowledgement in each paper of the presence of the other, or a third brief review/editorial possibly coauthored by some of the authors of each paper.

There's a great blog post that talks a bit about the process for simultaneous publications from the Vice President of Editorial at Cell Press (for those outside of biology, this covers some of the most respected journals in basic biology research): http://crosstalk.cell.com/blog/how-papers-from-different-groups-get-published-together

I'm not sure about the ethics overall, but it seems like the issue is being a part of both teams like this in the first place...you would have been aware of this way before the state of writing the actual papers. I think you certainly should have spoke up earlier in the process, at this point you may have already entered the "damage-control" phase, especially if the outcome ends up negative for either of the two groups (i.e., if they are unable to publish or end up publishing in a much lower journal).