The Army is spending $2.6 billion on hundreds of European-designed helicopters for homeland security and disaster relief that turn out to have a crucial flaw: They aren't safe to fly on hot days, according to an internal report obtained by The Associated Press.

While the Army scrambles to fix the problem — adding millions to the taxpayer cost — at least one high-ranking lawmaker is calling for the whole deal to be scrapped.

During flight tests in Southern California in mild, 80-degree weather, cockpit temperatures in the UH-72A Lakota soared above 104, the point at which the Army says the communication, navigation and flight control systems can overheat and shut down.

No cockpit equipment failed during the nearly 23 hours of testing, according to the Pentagon report, prepared in July. But the report concluded that the aircraft "is not effective for use in hot environments."

The Army told the AP that to fix the cockpit overheating problem, it will take the highly unusual step of adding air conditioners to many of the 322 helicopters ordered.

The retrofitting will cost at least $10 million and will come out of the Army's budget, according to the Army.

California Rep. Duncan Hunter, the ranking Republican on the House Armed Services Committee, told the AP that the lightweight helicopter will still have too many weaknesses.

"In my view, we would be well advised to terminate the planned buy of 322 Lakota helicopters and purchase instead additional Blackhawk helicopters," Hunter said in a letter this week to Army Secretary Pete Geren.

But Army spokesman Maj. Tom McCuin at the Pentagon said: "It's certainly a concern to people out there in the field now because it's hot in those cockpits, but it's being fixed."

The Army has received 12 of the Lakotas so far from the American Eurocopter Corp., a North American division of Germany's European Aeronautic Defence and Space Co., or EADS. Testing on the first six by an independent arm of the Pentagon revealed the problems. The rest of the choppers are scheduled for delivery to the active-duty Army and the National Guard over the next eight years.

The Lakota represents the Army's first major effort to adapt commercially available helicopters for military use. Air conditioning is standard in commercial versions of the aircraft, which have not had overheating problems. But the military usually avoids air conditioning in military aircraft to reduce weight and increase performance.

"We don't need air conditioning in the Blackhawks, so we didn't think it would be an issue" in the Lakota, McCuin said. "But when we got the helicopter into the desert, we realized it was a problem."

The Army plans to use the Lakota for such things as search-and-rescue missions in disaster areas, evacuation of injured people, reconnaissance, disaster relief and VIP tours for members of Congress and Army brass. All of its missions will be in the U.S. or other non-combat zones.

Blackhawks, Chinooks and other helicopters will still be available for more demanding duties, such as fighting wildfires or mass evacuations.

EADS spokesman Guy Hicks declined to comment directly on the criticism leveled against the aircraft. "We're proud of our partnership with the Army and the UH-72A, but we defer on anything to do with aircraft requirements and performance. It's the Army's program and they should address that," he said.

The commercial purchase was designed partly to cut costs and quickly get aircraft into the field to replace two aging Vietnam-era helicopters, the Kiowa and Huey. The Army said the Lakota will also free up more Blackhawks to send to Iraq for medical evacuation flights.

The Lakota has another problem: Testers said it fails to meet the Army's requirement that it be able to simultaneously evacuate two critically injured patients. The Lakota can hold two patients, but the cabin is too cramped for medics to actually work on more than one of them at a time, the testers said.

Also, the Lakota cannot lift a standard 2,200-pound firefighting water bucket, though it can handle a 1,400-pound one. The Army said it had no intention of using the Lakota to fight wildfires anyway. But Hunter said the military should be buying versatile aircraft useful in any domestic disaster.

The report by Charles McQueary, the Defense Department's director of operational testing, said that overall, the Lakota performs better than the Kiowa or Huey and pilots found it easy to fly.

But the report said inadequate ventilation, heat emitted by aircraft electronics and sunlight streaming through the large windows caused cockpit temperatures to reach 104.9 degrees during a simulated mission in California.

The report did not say how long the helicopter was in the air before it reached that temperature. The Lakota is supposed to be able to fly for 2.8 hours.

The aircraft's safe operating limit is 104 degrees, according to the Army. Beyond that, alarms may sound, signaling the pilot has 30 minutes before possible system shutdown, the report said. It said pilots should land as soon as possible or take other action to cool the cockpit.

Kim Henry, a spokeswoman for the U.S. Army Aviation & Missile Command at the Redstone Arsenal in Alabama, said that the Army began outfitting the helicopters with vents after the report was issued and that they have been effective at lowering temperatures.

However, the Army decided it still needs to put air conditioning on about a third of the choppers, including those bound for hot climates like the Southwest, and all of those configured for medical evacuations, McCuin said.

"The Minnesota Air National Guard probably doesn't need air conditioners," he said. The cost of an air conditioning unit per aircraft is about $98,000, McCuin said. Redesigns to add vents, scoops and other devices to increase cockpit ventilation for the rest of the fleet could add millions more.

Despite the needed fixes, McCuin and other officers familiar with the Lakota lauded the aircraft, pointing to parts of McQueary's report that found the aircraft does meet hovering, range, endurance and speed requirements.

The Army officials also stressed that the problems are being discovered and dealt with now, when just a few of the helicopters have arrived.

Loren Thompson, a military analyst with the Lexington Institute, a defense think tank in Virginia, said the Army is facing a new kind of criticism over the Lakota. Whereas the Army has been ridiculed for decades for overspending on aircraft, it now faces questions of whether it was too cost-conscious.

"The Army may be learning that its performance requirements are so demanding that adapting commercial helicopters is almost as hard as starting from scratch on a new military design," Thompson said.