Federal Aviation Administration Targets Boeing 737 Engine-Oil Leaks: WSJ

U.S. aviation regulators on Friday unveiled a proposed safety directive targeting maintenance errors that over the years have caused dangerous engine-oil leaks on more than three dozen Boeing Co. 737 aircraft.

The Federal Aviation Administration said it acted after receiving reports that 34 of the 737s—the world's most popular jetliner model—suffered "total engine oil loss" in one engine as a result of mechanics failing to replace a cap after routine ground checks.

According to the FAA, four other 737s experienced similar engines leaks with both of their engines.

Such leaks typically lead to engines being shut down by pilots to keep them from coming apart and to prevent fires. The incidents also sometimes led to emergency landings, though none resulted in accidents.

The leaks happened between 1986 and 2011, with the last incident involving loss of oil in both engines occurring in May 2011. The FAA's proposed solution is to mandate some of the same procedural safeguards and redundant checks mechanics have been required to use for many years when servicing engines on larger twin-engine jets flying long over-water routes.

But with some 7,000 of the affected planes operating world-wide—only a fraction of them equipped with modified seals to reduce the impact of such maintenance slip-ups—the FAA is moving to mandate heightened airline oversight of mechanics. Under the proposal, a second mechanic will be required to verify that the cap was replaced correctly.

Posted on the Federal Register website, the FAA's proposal covers 737 engines manufactured since the 1980s by CFM International, a joint venture between General Electric Co. And France's Safran SA.

The FAA's document indicates about 2,000 of the engines are installed on planes operated by U.S. airlines.

A GE spokesman said company officials have recognized the problem for at least two years, and voluntarily issued service bulletins urging 737 operators to heighten supervision over maintenance and install improved seals intended to prevent massive leaks even if caps are left off or end up secured improperly.

"With a population of engines that large," there are numerous opportunities for continuing mistakes by mechanics, according to GE spokesman Rick Kennedy.

On average, the caps are removed twice a year for routine engine inspections, Mr. Kennedy said.

In May 2011, the same month safety experts found out about the last dual-engine leak problem, CFM opted to take voluntary action and urged airline customers to be more vigilant. The engine maker also has been urging the FAA to make the company's service bulletin mandatory. An FAA spokeswoman declined to comment.

The agency's document said the proposed sign-off by a second mechanic "exceeds normal maintenance" requirements but "is necessary due to the design and location" of the cap.

The agency, which isn't looking to mandate installation of new seals, is setting aside two months for public comment.

Last October, European air-safety regulators mandated replacement of the cap with a new design and ordered mechanics to take special precautions when performing work that entails removal of the part.

That safety directive said taking off the cap must be considered a "flight safety sensitive maintenance" task, and must be followed by "an independent inspection of the correct installation" by a second mechanic.