21.   Air traffic control centers have extensive equipment to assure that they are never without electricity.

22.   Breakdowns at the control centers do not represent a threat to the public, Price said.

23.   But a duty official at the Russian mission control center declined to provide his name, or discuss any details and slammed down the phone.

24.   But an official of the union that represents electronics technicians at the control center where the problem occurred said the cause had been identified.

25.   But an operator is supposed to get approval from a control center before passing a red signal, and that rule apparently is not always followed.

26.   But now the control center is festooned with a banner from Hewlett-Packard, the computer company.

27.   But poison control centers around the country said they have seen a marked increase of DXM overdoses in recent years.

28.   By the time he reached the platform, the traffic control center had apparently decided otherwise.

29.   Calls to poison control centers in England, he said, can be made only by health professionals.

30.   Control over the air space was transferred to Dulles and to a control center in Leesburg, Va., Mr. Brenner said.