Russia investigates the crash of two planes last night: Investigators picked through the scattered wreckage today of two Russian passenger jets that crashed nearly simultaneously Tuesday night after leaving Moscow, and reported that they had found flight data recorders for both flights, officials said. At least 89 people died in the crashes, according to the latest tally provided by Domodedovo International Airport, from where both planes took off late Tuesday. As airport security was tightened throughout Russia, it remained unclear whether the crashes were an awful coincidence — a case of two jetliners leaving the same airfield and suffering catastrophic mishaps only minutes apart — or a carefully coordinated terrorist act that originated in Moscow's most modern airport. Russian officials emphasized that the causes for the crashes had not been found, and urged patience and calm. "The experts are working," Dmitri Peskov, a spokesman for President Vladimir V. Putin, said in a telephone interview. "They are in the field. But it is a little bit early to be clear of the cause of this great tragedy." Earlier in the day the Russian news service Interfax, citing an anonymous official, reported that minutes after the first plane went down, the second jet issued a distress signal indicating it had been hijacked. Then it, too, disappeared from radar. Mr. Peskov said he was aware of the report, and that it was being investigated. "It is part of the job of the experts," he said, but neither dismissed nor endorsed the account. "There is no necessity now for speculation," he said.