Make sequential groups of rows that surpass a minimum sum

Let's say I have a table with a timestamp (ts) and a value (a). With some sample data:

ts, a
1, 10
2, 30
3, 10
4, 20
5, 40
6, 10
7, 20
8, 30
etc

I would like to group rows, in ts order, by summing a and outputting a row where the sum of a is > 50. In this case, the output should be two timestamps (first and last row):

1, 3  -- 10 + 30 + 10
4, 5  -- 20 + 40
6, 8  -- 10 + 20 + 30

But I have no clue how to proceed. All attempts I did with Copilot yield complex code that never finishes.