For the sake of discussion, one could argue that the real issue Frontier faces is less about the frequency of flights (daily and/or year-round service) and more about proper network development.

Frontier currently has three key markets (four if you count OMA) and they should be focused on maximizing opportunities there as much as possible to build better brand awareness, increase market share, and leverage traffic flows as much as possible.

Using your example of GRB, Frontier doesn’t have to fly to DEN on a daily year-round basis because they also have flights to their other hub in MKE that should in theory provide connection opportunities to a majority of the route network as well (more on MKE below). The TUC schedule could be further enhanced with flights to MCI and/or MKE that connect to the Midwest and East Coast.

The issue of low frequency can actually be a big issue in some markets due to limited options and low network connectivity. BDL and RDU are two prime examples where Frontier probably handicapped themselves a great deal by offering limited flight schedules with few useful connections. If you originated in DEN, you only had one flight option going to either destination. This is hardly a useful or beneficial schedule for business travellers. For customers originating in either city, they are either cut-off from much of the network (especially the Western network) or have to make a double connection to get to many places. With schedules like that, you’re going to only attract the die hard Frontier flyer or the ultra price sensitive leisure traveller. Frontier should have either added a third flight to MKE and/or routes to DEN and MCI to capture both O&D and connecting traffic. Of course yield and revenue management is important here but you should be able to attract a better passenger mix with good scheduling options.

Setting aside the situation in MKE, Frontier seems to have some more opportunities in MCI that they simply haven’t pursued for whatever reason. Back when Midwest was still flying, they competed well against Southwest to places like SAN, MCO, and FLL. While yields were OK, the real issue Midwest faced was this it wasn’t economical to fly 88 seat 717s against Southwest 737s. Now Frontier had the right planes to commence this type of flying (and add things like LAS) but has chosen not to. At some point they need to decide if they will take a more aggressive stand against Southwest or simply chase after opportunistic flying (which there is less and less of).

Looking specifically at BKG, the bigger concerns I have is that this seems to be as a short-term move designed to take advantage of subsidized flying during the slow travel months in fall. If you’re an airline going into a market, aren’t you focused on more long-term objectives? The DEN-BKG route may be doing fine, but was does running AUS and PHX for a few months accomplish other than finding a profitable place to deploy excess lift? Maybe there’s something else in the works for BKG but if not it’s a bit scary to think Frontier can’t find better uses for this capacity. What happens if Southwest decides to go after some more markets in BKG?

Realizing network synergies is further complicated by the situation in MKE. I firmly believe (and have been told by a few people in a position to know) that much of the turmoil Frontier currently finds itself in is due primarily to the financial black hole at Mitchell Field. For the time being, Frontier has essentially ceded the West Coast, Vegas, and Florida to AirTran/Southwest (for those interested, I was told that AirTran lost big bucks in MKE this past winter as well). With every additional cut MKE becomes less attractive as a connecting point. Hopefully some yield relief is in store in the coming months, but time is not on Frontier’s side. With the secondary hub essentially on life support at the present time, there's not much for Frontier to fall back on.

There are other issues at play, of course, but there’s no reason to get into all of that again.