At least for Lufthansa, Air Canada, UAL
We've been tracking fares for a month, and I thought we did well to jump on a price drop last Thursday, for Lufthansa, it did disappear the next day. This was for Philadelphia to London and Amsterdam back to Philly, next April.
Because I am a bit OCD, I have kept following this. And today, again Thursday, the fares I saw not only came back, but were even substantially lower. As in our Lufthansa tickets now $768 (from $820, which I thought was great), and had we been willing to take Amtrak from 30th Street to Newark and back, United would now get us there for $694. Air Canada is also in the mix, in the lower $700s.
For curiosity I played with this for roundtrips from here to either LHR or AMS, and it was similar for these 3 carriers.
With Thursday being the day.
I will bet these are gone by later tomorrow, and will likely reappear next Thursday, or at least later next month on Thursday.
BTW, none of this affected the high-priced direct flights via US Air or the BA/American group, which while at a somewhat lower point, as in just south of $1,100, that I saw late July, they have been fixed in price over $1200 since then.