Start-up interisland airline go! said its planes were less than two-thirds full in August but the company's parent said the lower passenger count was no cause for alarm.

Phoenix-based Mesa Air Group, which owns go!, said its planes were 64.5 percent filled in August, which is down from 73.9 percent in July and 82.5 percent in June.

The airline, which began flying June 9, said it served 62,367 passengers last month, down from July's 69,680. Figures for June were not available.

Jonathan Ornstein, Mesa's chief executive officer, said the decrease was partly attributed to a seasonal decline in Neighbor Island travel.

He also said that go! put a fifth 50-seat jet into service last month that could have contributed to the lower percentage of filled seats. The additional jet, which won't be used in September, was to provide more seating for tour operators, Ornstein said.

Ornstein said the airline's overall performance in August improved as the company's on-time record got better and the airline expanded its seating capacity.

"Go! continues to perform extremely well," Ornstein said.

Go! touched off a price war when it opened for business in Hawai'i with $39 one-way interisland tickets, prompting Hawaiian and Aloha to match the fare. The airline also has offered one-way fares for a limited time at $29. Aloha and Hawaiian have matched go!'s fares each time it has announced a discount.

Aloha and Hawaiian have not yet reported August traffic statistics. But from January through July, the airlines' planes have been flying at more than 80 percent full.

The local carriers also have the industry's best on-time record. The U.S. Department of Transportation said yesterday that 95.8 percent of Hawaiian's interisland and West Coast flights were on time in July, which was tops in the industry. Aloha was next with a 92 percent on-time record.

Reach Rick Daysog at rdaysog@honoluluadvertiser.com.