Ask Captain Lim

Hello Captain Lim,

If an airplane encounters total engine failures during the flight, what will happen? Does the plane start flipping and crash, or it continues to fly while losing height, and how long does it last and how safe is to land?

Raid Asfour,
Australia

This is a very interesting question and I am sure many other non-aviators would be interested.

When all engines are failed during flight, not all hopes are lost my friend ! Have you ever heard of gliders flying ? Well, gliders fly without any engines! Okay, I am being too simplistic. Nevertheless, all aircraft can glide to a safe landing but the degree of distance flown varies. Gliders can stay in the air for a long time. Single engine aircraft encountering an engine failure can also glide a fair distance to execute a safe landing provided it has the height.

I am sure your question concern commercial aircraft. Firstly, I must say that all commercial aircraft engines are very reliable and to have all the two, three or four engines failed totally on them are very, very rempte. Of course, I am not going to argue with the Murphy's Law that, anything that can go wrong will go wrong.

Okay, I will tell you a true story or two. In 1983, a Boeing 767 belonging to a major Airline in Canada actually lost all their (only two!) engines in flight. The cause of the failure was not because the engines were technically faulty. It was due to human error ! You see, apparently the engineer in charge of refueling the aircraft interpreted the fuel request incorrectly. The pilot requested fuel uplift in kilograms, which is normal (rather than in gallons or liters) but the refueler read it as in pounds. Remember, one kilogram of fuel equals to about 2.2 pounds. So the aircraft had about half the fuel required to fly the distance. Consequently, the Boeing 767 ran out of fuel halfway and both the engines quitted on them !

Of course, the pilots should have realized the mistake but it was unfortunate that they missed the second chain of events which could have prevented the accident. What was fortunate was that, the pilot concerned used to fly gliders as a hobby. He happened to recognize a disused airfield nearby that he used to land before. He then executed a perfect forced landing without any loss of lives or aircraft.

The second story concern another major Airline from the United Kingdom. Its Boeing 747 was enroute from London to somewhere in Australia when it lost 4 engines due to volcanic ash spewing over the sky near Jakarta in Indonesia. Fortunately, the crew were able to restart (or relight in aviation term for jet engines) at least 2 engines when they were cleared of the volcanic ash at a very low level.

Your question was, when an airplane encounters all engines failure, does the plane start flipping and crash, or continue to fly while losing height? If it continues to fly, how long does it last and how safe it is to land the aircraft ?

As I have described earlier, the aircraft does not flip or crash. It continues to fly at an optimum gliding speed, a speed much lower than its cruising speed.

However, it may not be able to maintain its cruising altitude but continues to lose height at a rate of about 3500 to 4500 feet per minute. This will give an aircraft, cruising at 35,000 feet about 10 minutes to fly a distance of about 40 to 50 nautical miles. Remember, pilots have been trained to restart/relight the engines whenever they encounter total engine failures. If restarting the engines were unsuccessful, they would have no choice but to carry out a prepared forced landing - just like what the Canadian pilot did to the crippled Boeing 767.

If you were a passenger on board this ill-fated aircraft, how would it feel like ? Although I have never encounter such an experience as a passenger, I have practiced this exercise many times and have been tested thoroughly in the aircraft simulator.

This is what will likely happen if you are in the passenger cabin. Firstly, if both engines failed simultaneously (very, very unlikely, but normally one after another), the noise level will drop very rapidly. The cabin lights will flicker and may be a bit dimmer. If the aircraft auxiliary power unit (something like a standby generator-cum compressor) fail to start automatically, you will feel the slow depressurization in your ears. Oxygen masks will drop from the ceiling and an automatic emergency announcement will be made through the Public Address System shortly. The cabin crew will then brief you the emergency procedures for a possible Forced Landing or Ditching.

How safe is it to land ? In a Boeing 777, with both engines failed, it is still controllable even though most of the normal hydraulic system pressures would be lost. However, there is the emergency hydraulic pressures generated by the Ram Air Turbine system (RAT). The RAT will automatically extend when it senses both engines had failed. There are fan blades on the RAT which will turn to generate hydraulic and electric power as the aircraft glide forward at a speed of about 180 to 280 mph. The landing gears would be extended by the emergency alternate system and the aircraft has sufficient brake pressure to bring the aircraft to a complete stop using the emergency accumulator pressure.

In a nutshell, if an airplane encounter all engines failures, it is capable of gliding to a safe landing provided there is a suitable landing area. The landing gears would extend and the brake would still function to stop the aircraft safely. So all hopes are not lost !

Hope that answers your question.

Airbus 330 suffered two engine failures

On 8th August 2001, an Air Transat Airbus 330 en route from Toronto to Lisbon with 293 passengers and 13 crewmembers suffered two engines failures. The twin-engine aircraft is certified to operate under the ETOPS 120-minutes rule. This means that the aircraft is permitted to divert with one good engine to an alternate airport up to a maximum of two hours away. (about 850 nautical miles)

The Flight was cruising at 39,000 feet when the flight crew realized that there was an imbalance of fuel between the main tanks. They were concerned with the fast depleting fuel quantity and decided to divert to Lajes Field Airport, located on Terceira Island in the Azores, 850 miles west of Lisbon.

The crew then ascertained that there was a leak somewhere that had caused the excessive fuel loss. They then declared an emergency. When they were 136 miles from Lajes, the right engine failed. As the aircraft was drifting down on the good engine at 34,500 feet, they ran out of luck! The remaining engine failed on them as they were about 85 miles out from Lajes. The crew was uncertain as to whether they could glide towards a landing at the Airport and advised the Air Traffic Control that ditching at sea was a possibility.

The Airbus 330 became a virtual glider when all the fuel tanks were empty, causing both the engines to quit on them. It was very fortunate that they were able to glide towards the airport at night and touched down safely on the two mile-long runway. It came to a safe stop, not after bursting eight of its ten tires. There were some minor fires on the main gear wheels but the Fire Fighting Services extinguished them without any problems.

Only nine passengers and two crewmembers received minor injuries during the emergency evacuation. (See the Video Flying on Empty 'Tanks' below)

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