



Further, when seeking a helicopter pilot’s license, one has to practice landing using this no-power technique.  When practicing, instead of actually shutting the engine off completely though, they usually just turn the engine down enough to disengage it from the rotor.  This way, if the student encounters a problem during a no-power landing, the helicopter can be throttled back up to avoid an accident. Given that this isn’t an option during actual engine failure, it’s critical for helicopter pilots to practice this until they have it down pat.

A landing via autorotation is also sometimes necessary if the rear rotor blades stop functioning properly, no longer countering for the torque of the main rotor blades, so the helicopter will spin if the engine isn’t turned off.  Whether this happens and the pilot shuts off the engine or in the case of actual engine failure, once the engine drops below a certain number of revolutions per minute, relative to the rotor RPM rate, a special clutch mechanism, called a freewheeling unit, disengages the engine from the main rotor automatically.  This allows the main rotor to spin without resistance from the engine.

Once the engine fails or otherwise is shut off, the pilot must immediately lower the pitch, reducing lift and drag, and the helicopter will begin to descend.  If they don’t do this quick enough, allowing the RPM of the main rotor to drop too far, they’ll then lose control of the helicopter and will likely not get it back.  When this happens, it may well drop like a rock.  However, this isn’t typical because as soon as the freewheeling unit disengages the engine, the pilot is trained to respond appropriately immediately.

Exactly what the correct glide angle is to maintain optimal rotor RPM varies with different helicopter designs, but this information is readily available in the helicopter’s manual.  The glide angle also varies based on weather conditions (wind, temperature, etc.), weight, altitude, and airspeed, but in all cases a correct glide angle has the effect of producing an upward flow of air that will spin the main rotor at some optimal RPM, storing kinetic energy in the blades.

As the helicopter approaches the ground, the pilot must then get rid of most of their forward motion and slow the decent using the stored up kinetic energy in the rotors.  If done perfectly, the landing will be quite gentle.   They accomplish this by executing a flare, pitching the nose up, at the right moment.  This will also have the effect of transferring some of that energy from the forward momentum into the main rotor, making it spin faster, which will further allow for a smooth landing.  Because the flare will often need to be somewhat dramatic, the tricky part here is making sure that the rear of the helicopter doesn’t hit the ground. Ideally the pilot executes the flare (hopefully stopping most all the forward motion and slowing the decent to almost nothing), then levels the nose out just before touchdown.

Autorotation may sound like a fairly complex and difficult thing to do, but according to one instructor I briefly chatted with about this, it’s really not all that difficult compared to a lot of other aspects of flying a helicopter.  In fact, he stated that most students have a lot more trouble when they first try things like hovering, than they do when they first try a no-power landing.  Granted, this is partially because students don’t try autorotation landings until they are near the end of their training, so they are more skilled than when they first try a lot of other maneuvers, but still.  It’s apparently not nearly as difficult as it sounds and most of the problems students have just stem from being nervous at descending at a higher rate than normal.

You can see a video of someone executing a near perfect autorotation landing below:


Bonus Facts:

  • The word ‘helicopter’ derives from the Greek “helix/helikos”, meaning “spiral/turning”, and ‘pteron’, meaning ‘wing’.  This in turn gave rise to the French word hélicoptère and then the English ‘helicopter’. The word hélicoptère was coined in 1861 by Gustave de Ponton d’Amécourt.  The first documented instance of this term was in a patent application filed in April of 1861 in France for a steam engine powered helicopter, invented by Gabriel de La Landelle.
  • Before the invention of the freewheeling clutch, when engines failed on helicopters this would freeze the rotors, which of course made it so that the helicopter really would fall more or less like a rock.
  • The longest recorded autorotation was achieved in 1972 by Jean Boulet who was attempting to set an altitude record in a helicopter, which he did and which still stands today.  He managed to make it up to 40,814 ft. when his engine died due to the extreme cold (−63°C).  He then autorotated his way all the way to a nice safe landing.
  • Boulet had originally wanted to land his Lama helicopter on the top of Mt. Everest (29,029 ft.) to demonstrate its capabilities, but couldn’t get authorization to do so, so instead just decided to go for the world record in altitude in a helicopter, which he achieved as described.
  • There is actually a type of one seat, personal ultralight helicopter designed to fly using an autorotating main blade all the time.  This helicopter has an engine mounted on the back with a propeller, just like a regular airplane with a rear engine.  On top is a free-spinning rotor attached to no power source, positioned at a “pitched-forward” angle.  These craft take off much like a regular airplane, though usually not requiring nearly as much runway as the wind generated just from the rear engine is near enough to get the top autorotating blade to spin fast enough take off.  (I’ve personally seen one at an airshow take off near straight up with a head wind aiding it a little).  If the rear engine dies in these, they can be safely landed via the same autorotation method used in normal helicopters.
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  • Me

    Wow, thanks for this! It should make riding a helicopter a lot less scarier, if I were to ride one.

    • bob

      oright fam, chillin pillin.

      • Kabal


  • KO

    The last factoid references a gyrocopter (or autogyro), which predates the invention of the powered-rotor helicopter by more than a decade. Read up them, it’s quite interesting to see how they work.

  • Steve

    Yeah sure: Four people who died after a Super Puma L2 plunged into the North Sea off Shetland on Friday after a catastrophic loss of power!

    • Daven Hiskey

      @Steve: Well, you do need to land on, you know… land. 🙂

    • Kabal

      One incident doesn’t make something true

  • J Rob

    If the main rotor were to become damaged or fractured and detach from the aircraft.

    The Helicopter WILL drop like a rock.

    Helicopters are far more dangerous than plane, as if the engine on a plane becomes damaged and detaches, the plane can still glide to safety.

    What every one forgets it that the main Rotor on a helicopter can become damaged and if this occurs the helicopter will Drop like a Rock, as this eliminated any chance of autorotation

    • B.D.

      It’s true that a helicopter can autorotate, but if you are flying large twin engine rotorcraft, it’s probably going to hurt. And you’re right, if your rotor system is damaged, you’re pretty much done for. In fact, if you were to lose a blade, the resulting force would cause such a strong jolt it would kill you immediately, before you even knew you threw a blade. That centrifugal force a powerful beast!

  • Peter jones

    If the main rotor shaft fractures. The Helicopter will fall like a rock.

  • Pfft

    Do you realize how many plane crashes result from engine failure as well. Planes are no more safer. Generally speaking helicopters do have a better chance of landing in a malfunction. In a plane trying to find a landing strip good luck and have sufficient gliding power.

    As far as landing in the sea. There are copters that actually gave an inflatable sponsons for such emergency. Just saw such an instance on the news the other month. Hats off to the pilot.

    Bottom line your only as safe as the skill of the pilot. I think we can all agree on that.

    Btw. I know nothing of aviation.


  • Hugh

    My great-uncle, Harold Pitcairn, came up with some key innovations for the autogiro (or autogyro, gyroplane, gyrocopter, or rotaplane). He bought the U.S. rights to Juan de la Ciervas’ autogiro patents and in 1977 his estate won a $32 lawsuit against the U.S. government enforcing these rights on the miltary purchase of heliocopters based on autogiro technology.

  • אייל טנדלר

    Wow, It was a first hard to believe, but after seeing the youtube , Its one of those see in to believe it , recommend to see the video before reading .

  • pierre

    sprag clutch question. the bearings are not skateboard roller bearings. if the inner part is spinning one counterclockwise the rotors are free from the engine, clockwise the sprag holds inner and outer and they turn together. why dont the blades spin opposite direction?

    • Herbert

      Its called collective pitch…

  • David

    (ATP, CFI, MEI) Sadly this article misrepresents the facts. Yes, in the event that an engine simply ceases to produce power, a helicopter may land safely through auto rotation. That exercise is no less dangerous than a fixed wing AC looking for a suitable off field place to land. However, that disregards the fact that most mechanical failures are not simply a reduction in power output of the engine. They typically involve some catastrophic mechanical failure which will either creates inherent instability or uncontrollably of the (main or tail) rotors or the ability to control their collective pitch. That’s the equivalent of an airplane losing a wing on a fixed wing AC. In addition the fatality rate in helicopters is about 100X the published rate for commercial operations in fixed wing AC (NTSB Helicopter 1.48 1.69 1.39 1.48 1.60, Airline .011 .011 .000 .011 .016 for the period 2000-2004). Faulty premise, flawed argument, bad conclusion.

    • Herbert

      Yes, its called cyclic failure…

    • Heli Pilot

      Comparing accident rates of major airlines only to all helicopter rates, including general aviation, is not a fair comparison. Airlines are also 100x safer than general aviation fixed-wing.

  • Pingback: How Helicopters Are Designed To Land Safely When Their Engine Fails | Gizmodo Australia()

  • Philip Andrews

    As an autogyro pilot I have to smile at all the misconceptions and glib half-truths in the original article. In a Robinson R22 after engine failure, you have 0.97 seconds to lower the collective or you end up on your own downdraft and it’s irrecoverable. Whatever you do it’s irrecoverable on engine failure below 700ft – according to the operating manual. With larger aircraft and higher mass rotor systems you have a bit longer, but not much. First you’ve got to r ealize you have an engine failure, and then you’ve got to react to it.

    The big difference with autogyros is that they are always auto-rotating and it’s not a big drama if the donkey quits (the engine goes) you just glide down, but in a helicopter (with no wheels) it’s a whole different story. Yes you can practice it, but in RL, not so easy. Mechanical failure is also a biggy as all of the rotor systems are under huge stress (unlike those in an autogyro) due to the complexity and way of working of a helicopter such that a serious failure is much more likley.

  • Flyboy

    On my computer flight simulator, I crash more with the choppers-lol. Of course, I also wipe out on the 737 because I don’t land it right, and get killed in military dogfights as well (-;.

    BUT I think (and sites on the www Agree) that a backup lithium electric power system for both choppers and Cessnas is a Good Idea. Just a few minutes worth so they can land safely.

  • Mary Klausen

    I was thinking about safety precautions for helicopters – like Cirrus has a parachute – why couldn’t a helicopter be equipped with switch blade type wings that flip out from the bottom edge of the body or maybe even the landing gear in such a way that would help them glide down slow enough to possibly survive? The wings could be kevlar and bracing titanium or something- kind of fold up like a bat’s wing if the framing for it were strong enough to handle the snap of opening. I don’t know why they don’t have that. I would think they could be tucked into an aerodynamic housing tube that would just blast off or apart like an air bag being deployed and the wings would open up like crazy fast.

  • Alex

    Thanks but I still prefer wide winged planes if I can’t help flying……..

  • Alex

    I still would not ride a heli nevertheless 🙂

    of course, if properly done, that should result in a decent descent – check the text (and slow the decent using the…)