Welcome to FT.

From what I have read, the cash burn is much higher in December than other months because of these factors, most of which make sense:

Not many high-fare business travelers buy tickets (last minute purchases) between turkey day and Jan 1;

Most tickets for December holiday travel were paid for weeks/months ago (advance purchase fares);

Many vendors are now requiring Cash up front rather than extending trade credit;

and some others.

The factors listed above look like one-time hits to cash and cash burn should lessen in January (unless BK discourages travelers from buying tickets).