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 

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) 

Macedonian army Mi-8 helicopter fires rockets during a military exercise at Krivolak's training centre, 100 km (60 miles) from Skopje, July 30, 2009. REUTERS/Ognen Teofilovski (MACEDONIA MILITARY) 

Macedonian army Mi-24 helicopter fires rockets during a military exercise at Krivolak's training centre, 100 km (60 miles) from Skopje, July 30, 2009. REUTERS/Ognen Teofilovski (MACEDONIA MILITARY) 

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) 

Macedonian MI-24 army helicopter fires rounds during a military exercise at Krivolak's training center, 100 km (60 miles) shout of Skopje June 5, 2007. REUTERS/Ognen Teofilovski (MACEDONIA)