General Electric Co and other aircraft engine makers and regulators are studying the possibility of formulating limits for safely operating jet engines in volcanic ash, industry and regulatory officials said on Monday.

The newly-launched effort comes as authorities and airlines in Europe struggle to figure out when it will be safe to resume full transatlantic and other service disrupted by a lingering ash cloud spewed by an Icelandic volcano last week.

Some flights are scheduled to resume on Tuesday after delays that have cost frustrated global airlines $250 million per day in lost revenue, European and U.S. regulators said.

Passengers around the world have been stranded, and planes towed from gates to remote airport locations to wait out the worst global service disruption since the September 11, 2001, hijack attacks on the United States.

The primary safety concern is the potential for fine ash deposits to damage high-performing engines, which take in air to cool turbines. Ash can clog ducts and cause overheating and failure. Also, sucked-in glass particles in ash can melt and destroy rotating blades and other parts.

The absence of guidelines, or limits, for engine use in ash conditions have made it difficult to judge safety risks associated with the cloud disrupting travel and commerce in Europe.

We don't know what the acceptable (ash) concentration level is, said Bill Voss of the Virginia-based Flight Safety Foundation. There is no safe or unsafe.

The most often cited example of a dangerous ash encounter involved a British Airways flight that flew through an ash cloud over Indonesia in 1982. Its four engines lost power and the plane shed significant altitude before the turbines could be restarted.

Regulatory agencies, like the Federal Aviation Administration (FAA), are involved in the early study of ash engine limits and in the ongoing assessment of when full operations in Europe can resume.

The FAA is continuing to work with the European Union and is sharing technical information and guidance based on previous experience managing weather and volcanic events that have affected portions of U.S. airspace, the agency said in a statement on Monday.

GE and its CFM International partner, France's Safran SA, account for 20,000 commercial engines in service combined, Deb Case, a spokeswoman for GE's aviation unit, said.

Case said discussions with regulators were under way and there is no time frame for determining whether limits can be devised.

Some of those engines are installed on Boeing Co and Airbus aircraft plying transatlantic and European routes overshadowed by the massive ash cloud, which is continuously on the move and hard to fully avoid because it cannot be detected by radar.

GE, Britain's Rolls-Royce and Pratt & Whitney, a unit of United Technologies Corp , are global aircraft engine suppliers.

Their units are equipped on wide body jetliners affected by the cloud, including Boeing and Airbus models flown by American Airlines, a unit of AMR Corp , Continental Airlines , British Airways, and KLM, and Air France

GE last week sent a notice to airlines and other operators to inspect engines if they think their planes had flown through ash, Case said. The alert also included instructions for properly cleaning engines, if ash was found.

GE is also collecting air samples from sites in Europe, Case said.

(Reporting by John Crawley; editing by Carol Bishopric)

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