A recent controversy of regular operational error has also arisen for Phd.

In 1986, the latest year for which records are available, 281 of the 1,200 operational errors were caused directly or indirectly by communication mistakes.

Last year, a new manager made changes intended to cut expenses, and the controllers responded by reporting scores of operational errors.

But the union says the cases involved workers who had sought treatment for mental stress after operational errors and close calls.

That was a 5 percent increase in the number of such incidents, called "operational errors," compared with the preceding 12 months, when 720 were reported.

In fact, the connection between traffic levels and operational errors is unclear.

The ensuing rapid shutdown of the reactor led to operational errors.

The agency refers to controller mistakes as "operational errors."

Often, the pilots of airplanes involved in an operational error never know about it.

Mr. Day and other controllers concede that many operational errors are not reported.