I posted this on the most recent OAG thread, but I feel it is a relevant discussion here as well.
With NK ending their PHX - DEN service in May. I have the following thoughts.
NK's strategy in PHX hasn't really made a lot of sense to me.
PHX - DEN currently sees AA, F9, UA, and WN service in addition to NK. In May here are the following frequencies / pricing on this route (as of a search tonight 2/12/17):
AA: 4x (lowest priced fares from $57 - $188 one way depending on the day of the week)
F9: 2x (lowest priced fares from $50 - $128 one way depending on the day of the week)
UA: 6x (lowest priced fares from $43 - $129 one way depending on the day of the week)
WN: 10x (lowest priced fares from $43 - $83 one way depending on the day of the week)
A 1x daily city pair on NK where 4 other carriers combined have 22x daily flights is just not going to cut it, especially when it's not a high fare route to begin with.
I don't really understand NK's strategy for PHX. Looking at NK's other routes out of PHX, they fly PHX - DFW and seasonally PHX - ORD and MSP. They also formerly flew PHX - LAX but that route was cancelled in September with multiple AA, DL, UA, and WN flights and relatively low fares.
Every single one of NK's routes (and the LAX former route) has a minimum of 2 other competitors and high frequencies. PHX - DFW has almost a dozen AA flights to DFW and multiple WN flights to DAL. PHX - ORD has almost a dozen AA flights, multiple UA flights, a F9 flight and multiple WN flights to MDW. PHX - MSP has multiple AA, DL, SY, and WN flights.
The hassle of flying NK at low frequencies for barely any savings over the competitors who offer multiple frequencies, wifi, carry on baggage at no additional charge, and much more useful frequent flyer programs just doesn't seem worth it.
F9 seems to make PHX work as they've found some unserved or underserved markets. F9 is the only carrier flying PHX - CLE, COS, and CVG. In addition, F9's other markets out of PHX are traditionally higher fare markets, markets less susceptible to competition by automobile, markets with only one other competitor, or DEN and ORD which make more sense as F9 routes due to F9's stronger presence in PHX.
Of the ULCC carriers in the PHX area. G4 has found a niche of serving secondary markets from a secondary airport (AZA). F9 has found a niche of serving markets with decent O/D numbers but are either not served or under served by other carriers out of the main airport (PHX). NK hasn't found a niche and seems to have simply decided to add flights to the markets that have the most daily non stops from PHX with the hopes that it would work. LAX didn't. DEN didn't.