>>If, at an altitude of lets say 35,000 feet, and over land and hopefully nearby a capable airport, Can a airplane maintain flight by gliding without both engines<<
Most descents in a jet from high altitude are done at idle thrust. The airplane is quite literally "gliding" at that point. We call that "top of descent". It's a calculated point where we can pull the power to idle and glide down to a much lower altitude. We don't have to touch the power again until we level off at our new altitude.
Modern jet engines are extremely reliable. I've been flying big jets for 15 years and have never (other than the simulator) had one quit or had to shut one down. Most airline pilots can go their entire career without an engine failure.
Losing an engine in a two engine airplane is treated as an emergency by the pilots and ATC simply because you only have 1 running engine left. It's not because the airplane is not capable of sustaining continued flight on one engine, it is. If your down to only one of any major aircraft system it's treated as an emergency by all envolved...it's just precautionary procedure. The chances of losing both of the engines on a flight because of mechanical reasons is astronomical. The airplane can maintain a safe altitude/speed on just one engine.
Aircraft manufacturers do have provisions and procedures in place and pilots are trained in the unlikely event both engines do quit. Flight controls are still being powered, usually through a "RAT" (Ram Air Turbine) that drops down into the slipstream either automatically (B757/767)or manually (A300/310). An APU can be started to provide electrical power to avionics and bleed air for the pressurization.
Unlike what some movies and the media would have you believe, airplanes don't just simply drop out of the sky like an uncontrolled anvil as soon as an engine stops. They just become gliders....much like the space shuttle, only with better glide ratios!