Guess you will be wondering what happens to an airplane if fuel supply gets depleted during flight way above the sky.
Airplanes don’t just fall out of the sky if fuel supply finishes which causes the engine to shut down. Airplanes can glide a few miles with no engine powered on. If the airplane is high at altitude, an Oxygen mask will drop off the cabin so people can breathe easily till the airplane descends a little.
When an airplane runs out of fuel the engines stop. The engines provide all the electric energy and hydraulic pressure needed for a flight, so the airplane just shutdown.

There are incidents which took place due to an insufficient supply of fuel in an airplane.

Boeing 767 -233 of Air Canada also known as Gimli Glider pictured above successfully glided to emergency landing on a decommissioned runway in Gimli, Canada that had been converted to drag racing strip after losing its whole fuel middle of the flight, the photo was taken July 23, 1983.

This was caused by a unit conversion error, Most of the world uses the metric system i.e. meters, liters, etc. While a few countries e.g Liberia, Myanmar uses the imperial system of measurement i.e. gallons, pounds, etc.

Canada was one of the latter countries until 1970 when the nation began to change over. Metrication (as it was called) took some time fifteen years and maybe even more. One of the industries to change over late in the process was the airline industry, which given the expense and longevity of the equipment makes sense. On July 23, 1983, Air Canada Flight 143 was one of the earlier flights using the new metric units.

Unfortunately, Air Canada was undergoing a second change at the same time — smaller flight crews. Typically, there were three core members of the crew — the pilot, the co-pilot, and a flight engineer. Flight 143, though, didn’t have a flight engineer; the pre-flight fueling protocol, therefore, fell to the pilots. That protocol required them to convert volume (liters) into mass (kilograms or pounds, depending on the system you use) in order to figure out how much fuel you need to add to your plane. And they did exactly what they should have done — except they got the labels wrong. Instead of figuring out how many liters the plane needed to hit the required payload of 22,300 kg, the crew calculated how many liters were needed to hit 22,300 pounds.

Instead of 22,300 kg (27,770 L) of fuel, they had 22,300 pounds (12,598 L) on board — 10,100 kg, about half the amount required to reach their destination.

Luckily, the pilot and co-pilot were better at the flying part than the math part of the job. The pilot already has ten years of glider training under his belt, and his co-pilot had trained at Gimli during his days with the Canadian Air Force — and therefore knew the surroundings quite well. Together, the pair were able to land the 767 — gliding the last 60 miles (100 km) — touching down just an hour or so before nightfall. The plane — the Gimli Glider, as it’d henceforth be known — suffered some damage to its nose and blew out some tires, as seen above, but the passengers were pretty much okay. Ten people suffered minor injuries but, miraculously, there were no fatalities.

The Aviation Safety Board of Canada reported that Air Canada management was responsible for “corporate and equipment deficiencies“. Their report praised the flight and cabin crews for their “professionalism and skill”. It noted that Air Canada “neglected to assign clearly and specifically the responsibility for calculating the fuel load in an abnormal situation.”It further found that the airline had failed to reallocate the task of checking fuel load (which had been the responsibility of the flight engineer on older aircraft flown with a crew of three.) The safety board also said that Air Canada needed to keep more spare parts, including replacements for the defective fuel quantity indicator, in its maintenance inventory as well as provide better, more thorough training on the metric system to its pilots and fuelling personnel.

After almost 25 years of service, C-GAUN flew its last revenue flight on January 1, 2008. On January 24, 2008, the Gimli Glider took its final voyage, AC7067, from Montreal Trudeau to Tucson International Airport before flying to its retirement in the Mojave Desert in California

In April 2013, the Gimli Glider was offered for sale at auction, by a company called Collectable Cars, with an estimated price of CA$2.75–3 million. However, bidding only reached CA$425,000 and the lot was unsold.

According to a website dedicated to saving the aircraft, the Gimli Glider was scrapped in early 2014. Parts of the metal fuselage were made into luggage tags and are offered for sale by a California company, Moto Art.