Gliding to Safety
Two commercial jets which successfully did something they were not designed for
The photo above is a purpose-built glider, constructed from lightweight materials. Surprisingly, commercial jets can also glide, if they need to. From 1953 to 2021, it happened 37 times — 22 without fatalities.
How Planes Fly
Put simply, there are four forces working on the plane, two of which enable it to fly. As long as thrust (from engines) and lift (mostly from the wings) overcome the plane´s weight and drag (friction between air particles and the plane´s surface), it flies.
If you lose thrust or lift, you are in trouble. There are several reasons why engines can fail; the most common is running out of fuel. Like this:
Air Canada “Gimli Glider” — 23 July 1983
Boeing´s 767 first entered service in September 1982. Air Canada Flight 143, reg. C-GAUN, was a commercial passenger flight from Montreal to Edmonton, via Ottawa. It was almost new.
Her crew were: Captain Robin (Bob) Pearson (48, with 15,000 hours experience) and First Officer Maurice Quintal. They would become legendary.
At 20.00 hours, at 41,000 feet over Red Lake, Ontario, the pilots heard a low-pressure warning from their left fuel pump. Thinking the pump had failed, they switched off the warning. Then a warning came from the right pump.
They decided to divert to Winnipeg. Then both engines failed. Their Ram Air Turbine (RAT) started up, giving them emergency instruments, and hydraulic support. But gliding was not on their emergency checklist.
Luckily, Captain Pearson was an experienced glider pilot, and First Officer Quintal had served in the Royal Canadian Air Force, stationed at Gimli, Manitoba. Gimli was 45 miles (72.4 km) away; Winnipeg was 65 miles (104.6 km). Descending fast, they wisely chose the nearer option.
Neither pilot knew Gimli Base was decommissioned, and now a drag racing strip, with a big race underway. The plane approached silently. People at the race saw it just in time.
The main landing gear worked, but nose landing gear collapsed as they touched down, and two tires blew out. This helped them brake. A few passengers suffered minor injuries during evacuation, but the emergency landing was a success.
Why It Happened
Investigators found only 64 liters of fuel left, and no leaks. Such incidents are usually caused by a chain of errors and misunderstandings:
Air Canada was changing its fuel gauges from pounds/liters to kg/liters. The plane´s gauge was in kilograms; the person fueling the plane did not know this, and reported fuel density in lbs/liters.
The cockpit crew entered this into the Flight Management Computer. Needing 20.088 liters for the return flight, they left Edmonton with 5.000 liters. The Fuel Quantity Indication System incorrectly indicated adequate fuel. These errors were repeated in Ottawa.
The Inquiry found Air Canada´s procedures, communications, and training were inadequate, and recommended all the airline´s planes be immediately converted to kg/liter to avoid further confusion.
The pilots of the Gimli Glider were initially also blamed, but won an appeal. They were later awarded the first Fédération Aéronautique Diploms for Outstanding Airmanship. The plane was repaired and served with Air Canada until 2008, when it was retired.
Flight KL867–15 December 1989
KLM Flight KL867 was a 747–400, reg. PH-BFC, under six months old. This new design required no in-flight engineer, and had screens instead of analogue instruments. This plane was a “combi,” and could be converted to carry passengers, cargo, or both.
Her flight crew were: Captain Karl Van Der Elst (51, with 13,000 hours experience) and two First Officers, Imme Visscher and Walter Vuurboom. They left Amsterdam at 8.30am, destination Narita, Tokyo, refuelling at Anchorage, Alaska.
Eleven hours into the journey, they noticed dust in the cockpit, and a strange smell, probably Sulphur.
Volcanic Ash
A Boeing 747 has four engines; volcanic ash can cause them all to fail. It consists of solid particles, 2mm or less, with sharp edges; erupting volcanoes produce massive amounts.
This does not appear on weather radar of planes or ATC, because the particles are so small.
The electrically-charged ash particles are made of silicates, which melt at 1.100ºC. The temperature of a cruising jet engine is around 1.400ºC. The ash melts, then solidifies like glass, sticking to the interior and suffocating the engine.
Without air, the engine cannot combust fuel; it surges, then flames out.
This is what happened to KL867, flying at 25,000 feet through the 45,000 feet high ash cloud from explosive eruptions of Mount Redoubt. This is a 3.108 meter (10,200 feet) stratovolcano in Alaska´s Aleutian Range, 250 km (155 miles) from Anchorage.
Neither the pilots nor ATC had up-to-date information.
At first the cloud looked normal. The pilots tried to climb to 39,000 feet to avoid it but, one by one, the engines failed. The Captain tried to restart them, using extra power.
He gave the First Officers control of the plane, and continued to work at restarting the engines. As it got darker, First Officer Visscher, talking to ATC, mentioned smoke in the cockpit. The pilots put on oxygen masks. Then the plane started to descend.
The electrical systems worked sporadically. For the passengers, the lights came and went. As KL867 descended, the glass in the engines began to shatter. On his eighth attempt, Captain Van Der Elst succeeded — engines 1 and 2 (left wing) re-lit at 13,000 feet, and 3 and 4 (right wing) at 11,000.
KL867 made a forced emergency landing at Anchorage. All 245 passengers and crew survived, but the plane was badly damaged by abrasive ash particles.
Investigators found over 80kg of ash still in the engines. All four needed replacing, along with the windshield, internal systems, wing leading edges, avionics and electronics.
The cost of repair was over $80 million, but PH-BFC flew again until retirement in 2018.
Preventive Measures
A major factor was lack of information available to pilots and ATC. This, and similar events, led ICAO (International Civil Aviation Organization) to advise foundation of the Volcanic Ash Advisory Network.
There are now 9 centers worldwide. At the planning stage, flights can be re-routed, and if pilots encounter ash, they now have detailed action guidance available.
*Footnote:
Aviation works to resolve safety issues, but gliding isn´t always successful. According to my online calculator, 37 commercial planes had to glide. There were 454 fatalities, and over 3385 survivors (numbers on board are unknown for three flights) — 7.5 times as many as died.
If you are ever in a plane which starts to glide, you have a good chance of survival.
Sources:
https://en.wikipedia.org/wiki/List_of_airline_flights_that_required_gliding
https://simpleflying.com/gimli-glider/
https://skybrary.aero/articles/volcanic-ash
https://aviation-safety.net/database/record.php?id=19891215-1&lang=es
Geologyhub, about the volcanic ash incident https://youtu.be/lINhO5rHcNQ
