An Air Force team should be in Hawai'i by Monday to investigate a Dec. 22 midair collision between a C-17 cargo aircraft and KC-135R Stratotanker during refueling training off O'ahu, an official said.

Air Force officials here characterized the incident as "minor," but did not rule out contact between the fuselage of the 174-foot C-17 and tail of the 136-foot refueling tanker.

Both aircraft landed safely, although the Hawai'i Air National Guard tanker was reported to have gone into a momentary dive, causing some bumps and bruises.

The refueling boom and tail of the KC-135R received "minor" structural damage, officials said. The extent of damage to the C-17 was not released, although the plane was flying again in a couple of days.

Hickam base commander Col. William J. Changose, who also is the commander of the 15th Airlift Wing, was piloting the C-17 during the nighttime refueling.

The cargo carrier was flown from Altus Air Force Base in Oklahoma for training. Eight C-17s are being based in Hawai'i, and Changose and Brig. Gen. Peter S. Pawling, commander of the 154th Wing of the Hawai'i Air National Guard, are expected to pilot the first of the $200 million aircraft into Hickam on Feb. 8.

The accident and investigation come as Hickam Air Force Base prepares to be the first base outside the Mainland to house C-17s. The aircraft will be flown and maintained by the active-duty Air Force and Hawai'i Air National Guard in a unique partnership.

Changose and other Air Force officials have declined to give specifics of what happened, saying the safety board will make an official determination.

Changose was one of the first pilots in the Air Force to fly the C-17 and was twice rated as an instructor pilot. He was conducting instructor pilot requalification training at the time of the collision.

Changose grounded himself from flying late last month while the investigation is under way. It remains unclear whether he needs the instructor pilot rating to fly with Pawling as copilot on Feb. 8.

The safety board investigation was initiated by Hickam and the Air Guard and will be finished by the outside investigators. It should determine what happened and whether proper procedure was followed. It is unclear whether the C-17 flew too close to the tanker, or the tanker flew too close to the C-17.

Nighttime refueling is a stressful and potentially dangerous task with two big jets flying extremely close to each other. For size comparison, a Boeing 757-300 is 178 feet long — about the same as a C-17.

Gen. Paul Hester, commander of Pacific Air Forces, is expected to fly the first C-17 from Long Beach to the Marine Corps base at Kane'ohe Bay. Changose and Pawling will fly the aircraft from there to Hickam.

Reach William Cole at wcole@honoluluadvertiser.com.