The Airbus A340 had a "serious malfunction" one hour into the 15-hour flight from Berlin to Buenos Aires, Merkel said. The delay forced Merkel to miss the start of the G20 summit and a scheduled meeting with President Donald Trump.
"Luckily, we had an excellent crew and the most experienced pilot of the special air mission wing," Merkel said.
The aircraft lost communications for nearly an hour, forcing it to make an emergency landing in Germany's Cologne-Bonn airport. Finance Minister Olaf Scholz and a delegation of officials and journalists were also on the flight.
The aircraft still had the majority of its fuel so it was heavier than normal when it landed, causing the brakes to overheat. Fire trucks were on standby but weren't needed. Passengers were held inside the plane for more than an hour. Later, they boarded another plane to Madrid. Eventually, Merkel and the rest of the German delegation boarded an Iberia flight to complete the trip to Argentina.
The aircraft, named after German statesman Konrad Adenauer, has had failures before, The Aviationist reported
Merkel planned to meet with Trump, President Xi Jinping of China and Argentine President Maruricio Macri.
"We do not know yet whether these meetings can possibly be rescheduled for a later time," a German spokesman said.
The cause of the aircraft malfunction is being investigated but there's no evidence of anything criminal, the spokesman said.