How can an airplane fly upside down?

Can any commercial airplane fly upside down?

• I've seen questions asking if the A380 () and B747 () can fly upside down. I've seen military aircraft flying upside down, but is it possible for any commercial airplane to fly upside down?

• Answer:

  It sort of depends on what you mean when you say "commercial" aircraft. It also depends on what you mean by flown upside down. If you mean extended inverted flight then the answer is likely no. Extended inverted operation creates problems with fuel supply and oil supply for engines that are designed to be operated in a certain orientation. Aircraft that are required to fly inverted for extended periods of time require modifications to fuel and oil systems. I've flown in an L-29 jet trainer aircraft that allowed inverted flight for 30 seconds at a time due to engine oil sump issues. Rolling aircraft inverted temporarily is another matter. Even large aircraft like the A380 can likely be barrel rolled at a constant 1G. Rolling an airplane at a constant 1G would have nil effect on the fuel and lubrication systems for the engines. Bob Hoover, pilot extraordinaire and airshow pilot, performed a demonstration in a Shrike Commander twin engine airplane where he poured a glass of iced tea while barrel rolling the airplane at 1G (video here:http://www.youtube.com/watch?v=pMWxuKcD6vE ) The Shrike is an airplane that is operated commercially, meaning for profit by FAA licensed businesses so, yes, commercial aircraft can be rolled and flown inverted. If you are referring to large jumbo jet airliners, then I believe the answer is still yes, they could do so in flight test but operating restrictions by the airlines would likely preclude someone from ever rolling one of these aircraft intentionally in standard operations.