At about 2 a.m. last Friday, some Tempe residents were awakened by a helicopter circling over their neighborhood near McClintock Drive and Guadalupe Road. About 200 of them called Tempe police.

On Saturday morning, that helicopter returned. Tempe police dispatchers fielded about 100 calls.

But as of late Tuesday,no one could say just who was flying that helicopter or why it was hovering over a south central Tempe neighborhood.

The helicopter had been registered as a "military flight" but it's been difficult to learn much more, said Oddvar Tveit, an environmental quality specialist for the city of Tempe.

No, that helicopter wasn't from the Luke Air Force Base or Border Patrol or the National Guard or the Phoenix Federal Bureau of Investigation, officials told The Republic.

Representatives from the Tucson-based Davis-Monthan Air Force Base, Fort Huachuca in southeastern Arizona, U.S. Immigration and Customs Enforcement and local police departments denied their involvement too. The Scottsdale bureau of the Federal Aviation Administration refused comment when contacted Tuesday.

"It's kind of frustrating," said Duane Washkowiak, chair of the Tempe Aviation Commission, a citizen's group which advises City Council about the impact of aircraft noise.

Washkowiak's wife was startled out of sleep by the sound of the helicopter early Friday and he called police when he learned of her concerns.

A dispatcher told him it was a military operation, he said.

When he struggled to find out more, he called Tveit who works closely with the Aviation Commission.

As of Tuesday,Tveit said he had received at least four complaints about the helicopter noise. He was waiting and hoping to learn more about what happened.

"Unfortunately, we were not able to find out what sort of (military) operation this was," he said.

Tveit said he eventually determined that the helicopter appeared to be a Vietnam War-era Bell UH1 and its flight pattern was unusual both times it was reported in the neighborhood, Tveit said.

Radar confirmed that it flew in circles, he said.

Working with Phoenix noise abatement specialist James Davies, Tveit determined that the helicopter had taken flight at or near the Phoenix Goodyear Airport. It fell off the monitoring system Tempe shares with Sky Harbor Airport near the Loop 101 between Guadalupe and Elliot roads.

Reach the reporter at lisa.halverstadt@arizonarepublic.com