The airline, Hawaii's third-largest scheduled carrier, plans to lease up to four Irish-built Shorts-360 turboprop planes.

Timing is not yet firm, said Douglas Caldwell, a Mahalo spokesman. "We can start as early as May 20. We expect to have them all here by July," Caldwell said today.

The aircraft are configured to carry 36 passengers. Mahalo's existing fleet consists of seven ATR-42 turboprops, handling 44 to 46 passengers.

The airline said it is increasing its fleet in response to demand.

Mahalo began flying in 1993 under a license held by a mainland company and got its own license in 1994.

It now operates more than 90 flights a day, competing with the all-jet fleets of Hawaiian Airlines and Aloha Airlines and, at smaller airports, with the turboprop planes of Aloha's affiliate, Island Air.

Mahalo's fares are a notch lower than those of the others.

Last year, Mahalo made a cost-saving switch by turning in the company-owned fleet of new planes and shifting to leased aircraft that were slightly older.

Last summer, Mahalo added a seventh ATR-42.

Now it has an all-leased fleet, Caldwell said.

The airline last year also boosted its service by code-sharing agreements under which it carries Hawaiian Airlines passengers to smaller airports and Northwest Airlines passengers to Kapalua-West Maui.