An upgraded heavy Mi-26T2V helicopter, manufactured by Russian Helicopters company, part of Rostec State Corporation, is seen on the tarmac during a demonstration tour at Mil Moscow Helicopter Plant in Moscow Region, Russia April 3, 2019. Picture taken April 3, 2019. REUTERS/Tatyana Makeyeva 

Crew members of an upgraded heavy Mi-26T2V helicopter, manufactured by Russian Helicopters company, part of Rostec State Corporation, are seen during a demonstration tour at Mil Moscow Helicopter Plant in Moscow Region, Russia April 3, 2019. Picture taken April 3, 2019. REUTERS/Tatyana Makeyeva 

A crew member stands inside an upgraded heavy Mi-26T2V helicopter, manufactured by Russian Helicopters company, part of Rostec State Corporation, during a demonstration tour at Mil Moscow Helicopter Plant in Moscow Region, Russia April 3, 2019. Picture taken April 3, 2019. REUTERS/Tatyana Makeyeva 

An upgraded heavy Mi-26T2V helicopter, manufactured by Russian Helicopters company, part of Rostec State Corporation, is seen on the tarmac during a demonstration tour at Mil Moscow Helicopter Plant in Moscow Region, Russia April 3, 2019. Picture taken April 3, 2019. REUTERS/Tatyana Makeyeva 

An upgraded heavy Mi-26T2V helicopter, manufactured by Russian Helicopters company, part of Rostec State Corporation, is seen during a demonstration flight at Mil Moscow Helicopter Plant in Moscow Region, Russia April 3, 2019. Picture taken April 3, 2019. REUTERS/Tatyana Makeyeva 

An upgraded heavy Mi-26T2V helicopter, manufactured by Russian Helicopters company, part of Rostec State Corporation, is seen during a demonstration flight at Mil Moscow Helicopter Plant in Moscow Region, Russia April 3, 2019. Picture taken April 3, 2019. REUTERS/Tatyana Makeyeva 

An upgraded heavy Mi-26T2V helicopter, manufactured by Russian Helicopters company, part of Rostec State Corporation, is seen on the tarmac during a demonstration tour at Mil Moscow Helicopter Plant in Moscow Region, Russia April 3, 2019. Picture taken April 3, 2019. REUTERS/Tatyana Makeyeva 

A Mil Mi-26 heavy transport helicopter is seen flying during the Aviadarts competition, as part of the International Army Games 2018, at the Dubrovichi range outside Ryazan, Russia August 4, 2018. REUTERS/Maxim Shemetov 

Mil Mi-26 heavy transport helicopter and Mi-8 medium multi-role helicopter perform during a demonstration flight at the MAKS 2017 air show in Zhukovsky, outside Moscow, Russia, July 18, 2017. REUTERS/Sergei Karpukhin 

A Mil Mi-26 heavy transport helicopter and an Ilyushin Il-76 military transport aircraft perform during the International Army Games 2016, in Dubrovichi outside Ryazan, Russia, August 5, 2016. REUTERS/Maxim Shemetov 

A Mil Mi-26 heavy transport helicopter performs during the International Army Games 2016, in Dubrovichi outside Ryazan, Russia, August 5, 2016. REUTERS/Maxim Shemetov 

A Mil Mi-26 heavy transport helicopter performs during the International Army Games 2016, in Dubrovichi outside Ryazan, Russia, August 5, 2016. REUTERS/Maxim Shemetov 

EDITORIAL USE ONLY - NO COMMERCIAL OR BOOK SALES. A Ukrainian helicopter Mi-24 gunship fires its cannons against rebels at the main terminal building of Donetsk international airport May 26, 2014. Three Ukrainian helicopter gunships mounted a heavy attack on the rebel-held international airport terminal at Donetsk on Monday, firing rockets and cannon and throwing out decoy flares as militants shot at them from the ground. REUTERS/Yannis Behrakis (UKRAINE - Tags: POLITICS CIVIL UNREST CONFLICT MILITARY TRANSPORT) 

EDITORIAL USE ONLY - NO COMMERCIAL OR BOOK SALES. A Ukrainian helicopter Mi-24 gunship fires decoy flares over a residential area moments after attacking Donetsk international airport May 26, 2014. Three Ukrainian helicopter gunships mounted a heavy attack on the rebel-held international airport terminal at Donetsk on Monday, firing rockets and cannon and throwing out decoy flares as militants shot at them from the ground. REUTERS/Yannis Behrakis (UKRAINE - Tags: POLITICS CIVIL UNREST CONFLICT MILITARY TRANSPORT TPX IMAGES OF THE DAY) 

A Mil Mi-26 helicopter with the Alinghi 5 catamaran arrives in front of the Genoa port August 7, 2009. The boat was lifted from Lake Leman in Switzerland and carried to Genoa in Italy on the Mediterranean where the Swiss team will train for the America's Cup until mid-October 2009. Ras al-Khaimah, in the United Arab Emirates, will be the host country for the 33rd America's Cup that will start February 8, 2010. REUTERS/Stefano Rellandini (ITALY SPORT YACHTING) 

A Mil Mi-26 helicopter with the Alinghi 5 catamaran arrives in front of the Genoa port August 7, 2009. The boat was lifted from Lake Leman in Switzerland and carried to Genoa in Italy on the Mediterranean where the Swiss team will train for the America's Cup until mid-October 2009. Ras al-Khaimah, in the United Arab Emirates, will be the host country for the 33rd America's Cup that will start February 8, 2010. REUTERS/Stefano Rellandini (ITALY SPORT YACHTING) 

A Mil Mi-26 helicopter with the Alinghi 5 catamaran arrives in front of the Genoa port August 7, 2009. The boat was lifted from Lake Leman in Switzerland and carried to Genoa in Italy on the Mediterranean where the Swiss team will train for the America's Cup until mid-October 2009. Ras al-Khaimah, in the United Arab Emirates, will be the host country for the 33rd America's Cup that will start February 8, 2010. REUTERS/Stefano Rellandini (ITALY SPORT YACHTING) 

A Mil Mi-26 helicopter carries the "Alinghi 5" catamaran over the Grand-St-Bernard Path at the Swiss-Italian border August 7, 2009. The boat was lifted from Lake Leman in Switzerland and carried to Genoa in Italy on the Mediterranean where the Swiss team will train until mid-October 2009. Ras al-Khaimah, in the United Arab Emirates, will be the Host Country for the 33rd America's Cup that will start February 8, 2010. REUTERS/Denis Balibouse (SWITZERLAND SPORT YACHTING) 

A Mil Mi-26 helicopter carries the "Alinghi 5" catamaran over the Grand-St-Bernard Path at the Swiss-Italian border August 7, 2009. The boat was lifted from Lake Leman in Switzerland and carried to Genoa in Italy on the Mediterranean where the Swiss team will train until mid-October 2009. Ras al-Khaimah, in the United Arab Emirates, will be the Host Country for the 33rd America's Cup that will start February 8, 2010. REUTERS/Denis Balibouse (SWITZERLAND SPORT YACHTING) 

A Mil Mi-26 helicopter carries the "Alinghi 5" catamaran over the Grand-St-Bernard Path at the Swiss-Italian border August 7, 2009. The boat was lifted from Lake Leman in Switzerland and carried to Genoa in Italy on the Mediterranean where the Swiss team will train until mid-October 2009. Ras al-Khaimah, in the United Arab Emirates, will be the Host Country for the 33rd America's Cup that will start February 8, 2010. REUTERS/Denis Balibouse (SWITZERLAND SPORT YACHTING IMAGES OF THE DAY) 

A Mil Mi-26 helicopter carries the "Alinghi 5" catamaran over the Grand-St-Bernard Path at the Swiss-Italian border August 7, 2009. The boat was lifted from Lake Leman in Switzerland and carried to Genoa in Italy on the Mediterranean where the Swiss team will train until mid-October 2009. Ras al-Khaimah, in the United Arab Emirates, will be the Host Country for the 33rd America's Cup that will start February 8, 2010. REUTERS/Denis Balibouse (SWITZERLAND SPORT YACHTING) 

A Mil Mi-26 helicopter carries America's Cup defenders new catamaran Alinghi 5 after it was moved from its construction site in Villeneuve to Le Bouveret July 8, 2009. Alinghi have chosen a giant catamaran with a length of 27.4 metres (90 foot) and a mast of about 50 metres (164 foot) to face U.S. challenger Oracle for 33rd America's Cup races in February 2010. The boat will follow a development program over the next weeks on Lake Leman. REUTERS/Valentin Flauraud (SWITZERLAND SPORT YACHTING) 

A Mil Mi-26 helicopter carries America's Cup defenders new catamaran Alinghi 5 from its construction site in Villeneuve to Le Bouveret July 8, 2009. Alinghi have chosen a giant catamaran with a length of 27.4 metres (90 foot) and a mast of about 50 metres (164 foot) to face U.S. challenger Oracle for 33rd America's Cup races in February 2010. The boat will follow a development program over the next weeks on Lake Leman. REUTERS/Valentin Flauraud (SWITZERLAND SPORT YACHTING) 

A Mil Mi-26 helicopter lands America's Cup defenders new catamaran Alinghi 5 after it was moved from its construction site in Villeneuve to Le Bouveret July 8, 2009. Alinghi have chosen a giant catamaran with a length of 27.4 metres (90 foot) and a mast of about 50 metres (164 foot) to face U.S. challenger Oracle for 33rd America's Cup races in February 2010. The boat will follow a development program over the next weeks on Lake Leman. REUTERS/Valentin Flauraud (SWITZERLAND SPORT YACHTING) 

A Mil Mi-26 helicopter lifts America's Cup defenders new catamaran Alinghi 5 from its construction site in Villeneuve, southwest Switzerland July 8, 2009. Alinghi have chosen a giant catamaran with a length of 27.4 metres (90 foot) and a mast of about 50 metres (164 foot) to face U.S. challenger Oracle for 33rd America's Cup races in February 2010. The boat will follow a development program over the next weeks on Lake Leman. REUTERS/Valentin Flauraud (SWITZERLAND SPORT YACHTING) 

A Mil Mi-26 helicopter lifts America's Cup defenders new catamaran Alinghi 5 from its construction site in Villeneuve, southwest Switzerland July 8, 2009. Alinghi have chosen a giant catamaran with a length of 27.4 metres (90 foot) and a mast of about 50 metres (164 foot) to face U.S. challenger Oracle for 33rd America's Cup races in February 2010. The boat will follow a development program over the next weeks on Lake Leman. REUTERS/Valentin Flauraud (SWITZERLAND SPORT YACHTING) 

A Mil Mi-26 helicopter lifts America's Cup defenders new catamaran Alinghi 5 from its construction site in Villeneuve, southwest Switzerland July 8, 2009. Alinghi have chosen a giant catamaran with a length of 27.4 metres (90 foot) and a mast of about 50 metres (164 foot) to face U.S. challenger Oracle for 33rd America's Cup races in February 2010. The boat will follow a development program over the next weeks on Lake Leman. REUTERS/Valentin Flauraud (SWITZERLAND SPORT YACHTING) 

A Mil Mi-26 helicopter lifts America's Cup defenders new catamaran Alinghi 5 from its construction site in Villeneuve, southwest Switzerland July 8, 2009. Alinghi have chosen a giant catamaran with a length of 27.4 metres (90 foot) and a mast of about 50 metres (164 foot) to face U.S. challenger Oracle for 33rd America's Cup races in February 2010. The boat will follow a development program over the next weeks on Lake Leman. REUTERS/Valentin Flauraud (SWITZERLAND SPORT YACHTING) 

A Mil Mi-26 helicopter lifts America's Cup defenders new catamaran Alinghi 5 from its construction site in Villeneuve, southwest Switzerland July 8, 2009. Alinghi have chosen a giant catamaran with a length of 27.4 metres (90 foot) and a mast of about 50 metres (164 foot) to face U.S. challenger Oracle for 33rd America's Cup races in February 2010. The boat will follow a development program over the next weeks on Lake Leman. REUTERS/Valentin Flauraud (SWITZERLAND SPORT YACHTING) 

A Mil Mi-26 helicopter lifts America's Cup defenders new catamaran Alinghi 5 from its construction site in Villeneuve, southwest Switzerland July 8, 2009. Alinghi have chosen a giant catamaran with a length of 27.4 metres (90 foot) and a mast of about 50 metres (164 foot) to face U.S. challenger Oracle for 33rd America's Cup races in February 2010. The boat will follow a development program over the next weeks on Lake Leman. REUTERS/Valentin Flauraud (SWITZERLAND) 

A Mil Mi-26 helicopter lifts America's Cup defenders new catamaran Alinghi 5 from its construction site in Villeneuve, southwest Switzerland July 8, 2009. Alinghi have chosen a giant catamaran with a length of 27.4 metres (90 foot) and a mast of about 50 metres (164 foot) to face U.S. challenger Oracle for 33rd America's Cup races in February 2010. The boat will follow a development program over the next weeks on Lake Leman. REUTERS/Valentin Flauraud (SWITZERLAND SPORT YACHTING IMAGES OF THE DAY) 

A Mil Mi-26 helicopter lifts America's Cup defenders new catamaran Alinghi 5 from its construction site in Villeneuve, southwest Switzerland July 8, 2009. Alinghi have chosen a giant catamaran with a length of 27.4 metres (90 foot) and a mast of about 50 metres (164 foot) to face U.S. challenger Oracle for 33rd America's Cup races in February 2010. The boat will follow a development program over the next weeks on Lake Leman. REUTERS/Denis Balibouse (SWITZERLAND SPORT YACHTING) 

A Mil Mi-26 helicopter lifts America's Cup defenders new catamaran Alinghi 5 from its construction site in Villeneuve, southwest Switzerland July 8, 2009. Alinghi have chosen a giant catamaran with a length of 27.4 metres (90 foot) and a mast of about 50 metres (164 foot) to face U.S. challenger Oracle for 33rd America's Cup races in February 2010. The boat will follow a development program over the next weeks on Lake Leman. REUTERS/Denis Balibouse (SWITZERLAND SPORT YACHTING) 

A Mil Mi-26 helicopter lifts America's Cup defenders new catamaran Alinghi 5 from its construction site in Villeneuve, southwest Switzerland July 8, 2009. Alinghi have chosen a giant catamaran with a length of 27.4 metres (90 foot) and a mast of about 50 metres (164 foot) to face U.S. challenger Oracle for 33rd America's Cup races in February 2010. The boat will follow a development program over the next weeks on Lake Leman. REUTERS/Denis Balibouse (SWITZERLAND SPORT YACHTING) 

A Mil Mi-26 helicopter lifts America's Cup defenders new catamaran Alinghi 5 from its construction site in Villeneuve, southwest Switzerland July 8, 2009. Alinghi have chosen a giant catamaran with a length of 27.4 metres (90 foot) and a mast of about 50 metres (164 foot) to face U.S. challenger Oracle for 33rd America's Cup races in February 2010. The boat will follow a development program over the next weeks on Lake Leman. REUTERS/Denis Balibouse (SWITZERLAND SPORT YACHTING)