Would it be correct to say that if an aircraft is in mid-flight and all engines stop working, the plane can safely fly perhaps for hundreds of miles until it finds somewhere to land? i. e. It would not fall to the ground if the engines stopped. Are the engines only required for take-off? I would like to know if it is more difficult to fly a plane without the use of engines.
None of your assumptions is correct.
A multi-engine commercial jet without engine power will drop several thousand feet per minute. The pilot has perhaps 5-10 minutes at best to find a place to land.
While commercial jets have an auxiliary power source to keep the instruments and controls functioning without engines, the mere fact that the airplane is traveling only on momentum makes it more difficult to fly. A commercial jet is not a glider – it is designed to work with engine power.
I’ll leave it to the licensed pilots to add details.
When the engines on a commercial jet stop running the plane loses all hydraulic pressure. No hydraulics = no control over the plane. Fortunately at least some planes (I don’t know how many) have a last ditch backup in the form of a Ram Air Turbine (RAT) which drops out if the plane loses all engine power. The RAT, which gets its power from the planes forward motion and air passing through the turbine, provides just enough pressure in the hydraulics to maintain minimal control over the plane.
For an interesting take on what happens to a commercial jet read this story on the Gimli Glider where the exact scenario in the OP happens to a Boeing 767.
In short, loss of all power to a commercial jet is pretty serious business (and it’s probably pretty serious in almost any other plane as well although I’m sure some make for better gliders than others).
Hundreds of miles? Well, the Space Shuttle does it. But then, it has the altitude to trade for airspeed.
If the engine in an airplane stops, you don’t stop flying. Think of it this way: What happens if the engine stops in your car? If you’re on level ground you’ll coast some distance. If you’re going uphill, you’ll come to a stop more quickly. But if you are going downhill, then gravity will keep you rolling. Same thing in an aircraft. If you lose your power, gravity provides the “motive force”, if you will, to keep the air flowing over the wings. The wings don’t know if the engine is running or not. What you’re doing is trading your altitude for airspeed mush as a car on a hill is trading altitude for roadspeed.
Are engines only required for takeoff? That would be nice! But once you get to altitude you need power to stay there. There are four forces working on an aircraft: Lift, weight (gravity), thrust and drag. You need the engine to generate the thrust that overcomes drag to allow the wings to make lift to counteract gravity. So how does a glider fly without an engine to generate thrust? It uses its altitude. Gravity will pull the glider down, but in doing so it allows the airframe to move forward. Moving forward allows the wings to make lift. Glider wings are more efficient than those on your typical Cessna, so a glider can climb by finding thermals. If I understand it correctly (not being a glider pilot), the air in a thermal is rising faster than the sailplane is being pulled down by gravity.
Is it harder to fly an airplane with a failed engine? I haven’t had the “pleasure”. But as I said, the wings don’t know if the engine is running. Aerodynamically, the airplane will fly just fine. But when the ground is coming up at you at 1,000 feet per minute and you have no power to change your landing site decision, it will probably make the pilot uncomfortable. (What’s the propeller for? It keeps the pilot cool. If it stops in flight, the pilot starts to sweat.)
That’s why pilots say that when a fellow pilot crashes, they run out of height speed and ideas simultaneously.
As any student pilot knows, engine failures are part of the private pilot curriculum. Even when you know it’s happening, it’s still nerve-wracking when the instructor reaches over, yanks out the throttle, and says “your engine just quit, take us down.” It’s still possible for the plane to keep flying; aircraft have a “best glide speed” at which you lose the least amount of altitude and travel the greatest distance. As the others here have said, however, you’re just buying time to find a suitable landing location.
av8rmike: Actually, practice engine failures are quite fun in a helicopter. One of my favourite things.
Saying that you only need the engine to take off in an airplane is like saying you only need the engine in your car so you can leave the driveway. The engine makes the plane go. Most airplanes make terrible gliders.
I just had this mental image of dunmurry sitting on an airplane whose engines had just quit. While everyone around him is panicking, he thinks, “hmmm—I’ll bet the Dopers will know what to do in a situation like this! Should I put it under MPSIMS or General Questions? Hope the Board’s not too slow today, we’re losing altitude . . .”
This reminds me of a joke.
A 747 is crossing the ocean. The pilot announces on the PA system, “Ladies and gentlemen, we’ve had a little problem with our #4 engine and we’ve had to shut it down. Not to worry though, because this aircraft is perfectly capable of flying along on three engines. Unfortunately, this will delay our arrival by half an hour.”
After a short time, the pilot makes a similar announcement about the #2 engine. This time he says that their arrival will be delayed by an hour…
Soon, the pilot is on the PA again. Yet another engine was lost; but the aircraft will fly one one engine. He announces that their arrival at their destination will now be delayed by 90 mintues.
One exasperated passenger turns to another and says, “Jumpin’ Jesus on a raft! If that last engine quits, we’ll be up here all day!”
That’s true, but only if the auxiliary power unit (APU) fails as well.
kunilou had it right. Most if not all commercial aircraft have an auxiliary power unit, which is a small gas turbine meant to provide power to controls and instruments, as well as power to re-start a stopped engine in flight.
If all engines quit, the pilots would still be able to rely on the APU, as long as there was fuel available. If the reason that the engines quit was that the aircraft ran out of gas (as happend to the “Gimli Glider”), then obviously the APU wouldn’t be available either.
There was a case last year when an Air Transat Airbus A330-200 glided without engine power 85 nautical miles (almost 100 statute miles) in 20 minutes from 34,500 feet and made an emergency landing at Lajes Airport in the Azores with only a few minor injuries. http://www.aviationsafetyonline.com/articles/english/20010910_air_transat_13_minutes.html
A typical airliner’s best glide ratio would be around 16:1 (16 ft forward for every foot of descent), and would occur at an airspeed of something like 180 knots. If an engine failure happened at, say 33,000’, the airliner should be able to glide near 100 miles (i.e. a distance around 16 times its altitude), and would require around 30 minutes to do so.
Aircraft that require hydraulic pressure to operate their flight controls (i.e. large aircraft) typically have some way (e.g. air-driven turbine) to produce this in the event of total engine failure. I don’t know for sure, but it would surprise me to hear that an aircraft could be certified that wasn’t controllable without engine power.
I fly gliders (no engine) and they are easy to control. You need some way to get launched – the common methods are being towed behind a powered aircraft (you release the 200’ towrope when 2000 or so feet above the ground) and winch launching (sort of like being a kite). The way the various controls (ailerons, elevator, rudder) work is almost exactly the same with or without an engine.
Landing is a bit different. In a powered plane, the approach path can be adjusted with engine power. In a glider, you have spoilers that give extra drag and allow you to touch down where you choose. You get just one chance, but with practice it’s not too tough.
Gliders are definitely not the same as powered aircraft - a glider is light enough and graced with long enough straight wings (to maximize lift) to do as its name implies. If you’re not in a glider, you can’t count on thermals to keep you in the sky - in fact, you’ll lose altitude fast in most powerless powered aircraft. IF the engine(s) quite in a powered aircraft, the pilot immediately starts looking at his options for an emergency landing.
I’m a pilot, and I’ve done a dead stick landing.
Engine-out landings are pretty standard practice for us Private Pilots. However, it’s usually done with the engine on, but at idle power. Sort of like in a car if you just took your foot off the gas completely.
However, I got to a point where this practice just wasn’t getting my heart rate up enough. So I decided to try it for real. I climbed up several thousand feet over a seldom used airport and… shut off the engine.
In a small plane such as I fly, there is no difference in control. It will fly just fine. However, on a landing approach, one gets an increased sink rate. The plane I fly has short wings and comes down briskly at idle power, so on this day I had to flare aggressively to arrest the descent.
The interesting part for any pilots here is this: I had read that in actual emergencies, pilots are anxious to not come up short of their intended landing site. Consequently, one is more likely to OVERSHOOT the landing. I found this to be true the day I tried it. I was over a 6000 foot runway, and used half of it! Normally, I can land the plane in 500 feet or less. But with the engine actually off, I wanted to be certain I had the runway and came in high. I was stunned at how much concrete I had used up. This realization in itself was worth undertaking the exercise of an actual dead stick landing.
Gassendi: My instructor told me to “make” the middle of the runway. Once I had that made, I could slip it down to the numbers.
Of course, nowadays I don’t need no stinkin’ runway!
Hydraulics: You guys are all about half right.
Modern airliners have two, three, or four separate hydraulic systems, each run by a combination of electric motor-driven pumps and engine-driven pumps.
737s, and I believe MD-80s and MD90s, do not need hydraulic power to land. The 737 is a so-called “manual-reversion” airplane, and when the two main hydraulic systems fail, the pilot still has a direct mechanical connection to the elevators and ailerons and can continue flying the airplane. Backup power for the rudder is a little separate hydraulic pump (the “Standby” pump), and if you lost engines, you’d lose that, since you’d have no electrical power to power it, but you don’t really need rudder anyway unless you get into a severe crosswind landing situation.
757s and 767s are fully hydraulic airplanes, and the pilot does not have any direct mechanical connection to the ailerons/elevator/rudder. However, the airplane has a Ram Air Turbine (RAT), which is a little hydraulic pump with a propellor on it. The RAT automatically swings out into the airstream after dual engine failures (or can be deployed by the pilot) and provides sufficient hydraulic power for “continued safe flight and landing.” The valves that admit the hydraulic fluid to the flight control actuators are commanded by cables pushed/pulled by the pilot, and so a 757 or 767 can fly with no electrical power whatsoever.
747s do not have a ram air turbine, but it turns out that if the engines fail, there’s enough hydraulic power generated by the “windmilling” engines to safely fly the airplane. On the 757 and 767, we were unable to show that windmilling engines gave enough power, so we added the RAT. Aagain, the valves are actuated by cables.
The 777 is a little more complicated. It also has a RAT, but the valves are electrically actuated,so in addition to the little hydraulic pump, the RAT has a little electrical generator to provide power to operate the valves.
Okay, one typo and one technical error; about par for the course.
Technical error: The 767 and 777 have (in addition to electric motor-driven pumps and engine-driven pumps) air-driven pumps. Air-driven pumps are run by engine bleed air, and are an abomination unto the Lord (IMHO) 
An instructor one taught me a neat emergency landing trick with Cessna’s. It would probably work with any plane having the same type flaps as the Cessna.
With engine out come to the field with enough altitude to ensure that you can make it. Then lower full flaps and lower the nose to make the desired landing spot or to maximum flaps-down speed.
When close to the ground flare out and with full flaps down there is so much drag that you lose the excess speed rapidly. With full flaps and diving at max flaps-down speed the thing comes down like an elevator.