MANILA, Philippines -- A virtual security buffer shielded the Makati Central Business District for three hours Friday after the Air Transportation Office (ATO) declared the area a no-fly zone as thousands gathered for one of the largest rallies staged against President Gloria Macapagal Arroyo.

The directive effectively prevented the ABS-CBN helicopter Skypatrol from flying over the area for a full, aerial view of the size of the crowd at its thickest.

Citing “security reasons,” the ATO issued a notice to airmen barring flights over the Makati business district from 5 p.m. to 8 p.m. at the request of the Philippine National Police, said ATO Executive Director Daniel Dimagiba.

“That's for security reasons, so that no one would suspect that those flying by are taking pictures, doing surveillance to identify them (protesters). It might just be misinterpreted,” Dimagiba said when reached by phone Friday afternoon.

Such an order was never issued in previous rallies against Arroyo, most notably massive protests in July 2005 and February 2006. Air traffic controllers, meanwhile, could not remember a similar notice being issued in recent years, not even at the height of protests against then President Joseph Estrada.

The ATO Manila Control Tower said Makati's air space is ordinarily restricted because of tall buildings in the central business district, but helicopters are allowed over the area as well as to land and take off from numerous helipads.

Dimagiba said the PNP operations office sent him a request to issue a “no-fly zone directive in the Makati business district and its vicinity,” what the police called “the projected rally area” in its letter.

The ATO readily granted the request and imposed the flight ban, saying it was a “precautionary measure” to prevent the public from being suspicious about flights over the area. Besides, he said, aircraft light enough to fly over the CBD -- mostly choppers -- could fly only before sunset.

A copy of the ATO letter to the Philippine National Police directorate for operations which the Philippine Daily Inquirer obtained showed that the aviation office granted the PNP request on the same day it was sent by fax on February 27. The letter, signed by Dimagiba, was addressed to Chief Superintendent Silverio Alarcio Jr., acting operations director.

The ATO directive hampered the coverage of media network ABS-CBN, which planned to send the chopper Skypatrol over the CBD area for a complete view of the rally site.

“We wanted to show the extent of the crowd estimate. It would have given us a clearer view of where the picket ends. We have a camera at Ayala Tower but we can't pull out, we don't know where the [crowd] ends,” said Chari Villa, head of the network's news gathering team.

ABS-CBN got wind of the directive through a copy of the notice the ATO sent to Skypatrol's hangar at the general aviation area of the Manila Domestic Airport, Villa told the Inquirer.

“I was surprised that they gave us that order. We are usually able to cover in that area... we did in previous rallies,” said Villa.

Ricky Velasco, Skypatrol's regular on-board reporter, said his team was allowed to fly over the rally area between 2 p.m. and 4 p.m., but were told by the ATO Manila Control Tower to pull back from CBD shortly before 5 p.m.

The TV chopper thus missed prized shots of the crowd as it started to swell.

One of two Philippine Air Force choppers that flew on a reconnaissance mission at 4:45 p.m. was also barred from entering CBD air space.

On a mission to survey the rally area, a UH-1H chopper of PAF's 207th Tactical Helicopter Squadron was advised to pull out of the Makati area as it approached the CBD. Its tandem plane, a Huey 2 of the PAF Search and Rescue Group, managed to penetrate Makati air space despite the directive, the control tower confirmed.

The first Huey, which carried three members of the media and PAF information office photographers, was only able to pursue the aerial survey in the quieter areas of Taguig, Pasig, and Quezon City.

The only gathering those on board the chopper saw from above was a thick line of people on each side of Commonwealth Avenue and people huddled around stalls along the roadside market.