Airlines High on Commuter Aircraft Use : Air travel: Business in Orange County is taking off for four regional carriers that are partners to larger companies. Small lines fly as if they were part of the big ones.

Investment banker Russell Diehl is a frequent flier. But with increasing frequency, when he flies it is not in a jet but in a 19- to 37-passenger turboprop plane.

Diehl is among the growing ranks of business executives on the go who have found the best way to get from here to there is often not on a jumbo jet. Instead, they rely on commuter airlines which now handle much of the major airlines short-haul traffic.

And nowhere in the country is the use of commuter flights growing faster than in Orange County, where four commuter carriers--regional partners to larger airlines--are enjoying a boom in business.

For the first nine months of the year, commuter aircraft flew 24,967 takeoffs and landings at the county’s John Wayne Airport--a 15.5% increase from the first nine months of 1989. Nationally commuter traffic is estimated to be up 6% this year, according to the Regional Airline Assn.

WestAir Commuter Airlines in Fresno, which is a partner of United Airlines and flies as United Express, said its Orange County passenger traffic in September was 50% higher than in September, 1989.

And Skywest Airlines, which is a partner of Delta Air Lines and flies as the Delta Connection, said Orange County passenger loads for the first nine months were up 18.2% from the first nine months of 1989.

“And that doesn’t count a really big increase in October” that hasn’t been announced yet, said Steven Hart, director of market planning for the Salt Lake City-based carrier.

Wings West Airlines, a commuter carrier owned by AMR Corp., the parent of American Americans, and States West Airlines, which is a partner with USAir, would not discuss their Orange County operations. Wings West flies as American Eagle and States West as USAir Express.

Commuter carriers have been growing for the past decade--a product of airline deregulation that enabled the major carriers to pull out of smaller, uneconomical markets and created a vacuum that regional carriers moved in to fill.

The commuters soon began affiliating with the major carriers and, in an arrangement called code-sharing, most now fly as if they are part of a major airline.

Passengers booking a Delta flight from Orange County to Atlanta, for instance, are likely to fly first in a small turboprop plane to Los Angeles International airport. The turboprop out of John Wayne Airport is owned by Skywest Airlines. But on passengers’ tickets, it is listed as part of the Delta flight.

The system enables the major carriers to devote their resources to “bigger markets and more lucrative routes, which are the long-haul flights,” said Mark Peterson, spokesman for WestAir. “And that has opened the short and medium flights to commuter airlines like us.”

But as with almost anything affecting John Wayne Airport, the reasons for the unusually large hike in commuter traffic in Orange County this year are complex. Because of the incredibly tangled web of legal actions and lawsuit settlements that make the airport the most tightly controlled and regulated in the United States, carriers there operate under all sorts of constraints.

For the regional airlines that operate in the county, that has meant there often has been more demand than capacity.

That began changing earlier this year as the annual limits on the number of passengers commuter lines could carry began increasing. As part of the $310-million airport expansion, commuters were granted a 50% hike this year to about 300,000 total passengers from 200,000 in 1989. An airport spokeswoman said the commuter carriers’ passenger limit could soar to 400,000 without causing problems.

And the commuter operators seem to believe that they soon will be able to use all of that capacity. Some are adding flights to or from Orange County in coming months and others are replacing small planes with larger ones on their most popular routes.

Commuter airlines aren’t always looked upon favorably by passengers--the planes are smaller than jets and as such provide less head room and often less leg room and are more prone to bounce about in rough weather.

“There is resistance in marketplace to smaller aircraft,” said Edward Martel, a spokesman for Wings West. “We are seeing rising expectations among customers for service and amenities. And we are trying to give them the airplanes they want, with pull-down trays and storage both under and over their seats.”

By the middle of next year, he said, American Eagle will be replacing some of its 19-seat planes with 34-passenger turboprop aircraft that have more storage and headroom.

But while passengers don’t always think of the commuters as one of the greatest innovations in air travel since the closed cabin, the major airlines certainly do.

“They give us tremendous flexibility to serve areas we could never serve economically with the bigger jets,” said Larry Pickett, a spokesman for USAir.

Beginning Dec. 1, the airline will cancel three daily jet flights between Stockton and Los Angeles and three daily round trips from Monterey to Los Angeles.

USAir’s commuter affiliate, States West Airlines--which flies as USAir Express, will replace those flights with four daily flights to Stockton and five to Monterey. Instead of the 81-seat jets that USAir was flying--often less than half-filled--USAir Express will be using 37-passenger turboprop planes.