Mexico, Cincinnati and Frankfurt are three of the flights that will no longer be boarding at PDX International. There were more changes to nonstop service routes than usual in the last 18 months, says air service development manager David Zielke. Decreased passenger volume is one reason, but it’s not the only consideration when airlines decide which cities are in or out.

Klamath Falls, North Bend and Pendleton were momentarily without service after Horizon upgraded from 37-seat planes to 70-seaters and had to dump the low-volume routes. Service to Klamath Falls and North Bend was quickly reinstituted by Skywest/United Airlines, which got “revenue guarantees” from the airports that covered any losses the airline might incur as its new routes got off the ground. (Skywest announced in August that it no longer needs the North Bend subsidy.)

The upstart SeaPort Airlines picked up service to Pendleton along with a federal subsidy as part of the U.S. Department of Transportation’s “essential air service” program that funds service at small airports. SeaPort also saved money, and time, on its new route to Boeing Field by using planes with fewer than 10 passengers, which are exempt from TSA security requirements.

Mexicana Airlines eliminated all direct flights to Mexico after a perfect storm of new passport requirements, economic turmoil and reports of drug violence converged to discourage ridership. Service over the northern border has fared better: Air Canada launched a new route to Calgary, which airport director Bill Wyatt expects will be profitable due to a high number of business travelers and the fact that travel to Calgary has historically been lengthy and inconvenient.

The announcement of a new direct flight can get people to fly, but service changes don’t otherwise have a big impact; most will settle for a layover.

ADRIANNE JEFFRIES