An electric glitch severed power supply to Sheremetyevo Airport for almost four hours Wednesday, causing the delay of 30 flights.
A construction crane came "unacceptably" close to the power lines that feed the airport, which produced a short circuit at 8:52 a.m., Moscow United Grid Company said in a statement.
"The cause of the glitch at Sheremetyevo Airport was a violation of the rules for working near power lines by an external organization," the statement said.
It didn't identify the company that operated the crane.
The state-controlled airport said it "promptly" switched to a back-up power supply, but Terminal D, a base for Aeroflot's flights, did go offline for a while.
Aeroflot said the airport couldn't start its back-up electricity generator immediately to ensure an uninterrupted supply. As a result, check-in and passport control systems malfunctioned, the airline said.
The systems began coming back online about a half hour later, it said.
Aeroflot said it had to delay a total of 30 flights and move some of its departures, to destinations like Paris and Munich, to other terminals.
Sheremetyevo said things got back to normal by 5:30 p.m.
Aeroflot said it would sue the airport. An airline spokesperson said it didn't yet have an estimate for the damage it incurred, adding that Aeroflot would first offer an out-of-court settlement, Interfax reported.
The grid company said the affected power lines didn't require any repair.
Sheremetyevo said it would, in turn, consider suing its electricity provider.
The Moscow City Transport Prosecutor's Office opened an investigation into the accident.
The Energy Ministry said it is considering creating a working group that would investigate the accident and offer measures to prevent such glitches in the future.
Eyewitnesses at the airport said some cafes and duty-free stores were not working for a while. Throngs of people were running from Terminal D to catch their flights, which had been moved to the other terminals.
Roman Gusarov, editor-in-chief of web portal Avia.ru, said Sheremetyevo's back-up power capacity was obviously insufficient to cover the newest Terminal D, Rosbalt reported.
The terminal opened in November 2009 and initially belonged to Aeroflot and state-controlled banks VEB and VTB. They merged the terminal into Sheremetyevo Airport by April and received shares in it.
The state still dominates in the airport's current ownership breakdown, with 83 percent. Aeroflot is the second-largest shareholder, with 9 percent.
The worst airport blackout in Moscow took place at Domodedovo Airport in December 2010. An icy rain caused power lines to snap, cutting off electricity supply for almost four days. Airlines cancelled or delayed hundreds of flights at the time.
Sheremetyevo expects its passenger traffic to grow to 25 million people this year, director Mikhail Vasilenko said last week. Last year, the number was 22.5 million people.
The airport has also announced plans to become the best airport hub in Europe by 2015. It is the country's largest airport with flights to more than 200 destinations.
Sheremetyevo, where the state plans to build a third runway, raked in 2.3 billion rubles in profit last year.