I emailed crew planning about this exact issue.

This is the response:

"The FLAG/DOM rules are as follows:

1. 100 hours in a month if you are assigned all of the time as part of a two man crew (121.481).

2. 100 hours in 30 consecutive days if you are assigned as part of a two, three, or four man crew (121.487).

3. 120 hours in 30 consecutive days if you are assigned exclusively to a three and four man crew (121.483).

Be aware that we still have segments that operate under Supplemental rules. If a segment operates under Supplemental rules, 100 hours in 30 consecutive days apply (121.503), and 120 hours in 30 days apply if assigned exclusively to a three or four man crew (121.521)"

That is the goods.

So the real hitch is when you fly a combination of trips that are 2, 3, and 4 man crew segments. 121.487 is the most restrictive (and also the most difficult to avoid as it takes some ciphering) with a 100 hour limit in 30 consecutive rolling days. So buyer beware if you fly a combination of FO and RFO trips.

Also note when crew planning uses the word "month" that should mean a calendar month as defined by the FAA, not a bid month. These are two different things that could become a problem with carryover and five week bid months.

It sure would be nice to have a way to bid around this. BidX Mobile has a "Check block in 30" option but even PH says it is not bulletproof. The word on the street is that the company uses a rolling 95 hours in 30 days (for 2,3, and 4 man crewed trips) during bid processing to determine legality so that is the number I use.

YMMV.