A U.S. Army study said power failures, or brownouts, caused 50 percent of serious accidents involving the Apache attack helicopter on combat missions in Iraq.

The study said the brownouts took place during take-offs and landings in Iraq.

An army The AH-64 Apache Apache has been a leading helicopter among Middle East allies of the United States. Egypt, Israel, Kuwait and Saudi Arabia have deployed the Apache and Israel plans to purchase additional aircraft, Middle East Newsline reported.

Commissioned by a congressional committee, the army study said half of the eight accidents termed catastrophic during the war in Iraq were caused by brownouts. The other half stemmed from a failure of the auxiliary power unit clutch.

The report also reviewed the four less serious accidents of the Apaches. Again, three of those accidents were attributed to brownouts.

Seven accidents were reported in the least serious accident category.

The report attributed three accidents to human error, three due to materiel failure and one weapons-related.

The report said the army has launched an effort to prevent power failures during the flight of the Apache. The measures included conducting what the report termed "infrastructure improvements as well as revised procedures and improved risk management in operations involving dust landings or take-offs."

The army was also performing engineering adjustment to the auxiliary power unit clutch failure. At the same time, the army has ordered inspections to detect potential failures.