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With the advanced rocket technology that SpaceX uses in the Falcon for re-entry and controlled descent, could the same technology be used in commercial aircraft? I'm asking about using it in emergencies like engine failures, stalls, loss of pitch control etc. in order to prevent a crash, or at least minimize the damage and reduce the fatality rate.

For fuel storage, the rockets could burn what's available in the tank without any need for an auxiliary tank dedicated to them.

I know that there is a similar technology used in the military: the C-130 Rocket Assisted Takeoff (JATO). But it's only used for short runway landings and take-offs.

EDIT:

The question is specific to thrusters that could recover the airplane from unrecoverable situations (dive, bank, upside down,...). Question Why are movable rocket thrusters not used in airplanes? answer is generic and not detailed for such use case.

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    $\begingroup$ I don't see why that would even need to be used since an airplane without engines is a glider and gliders fly well. And about the "stall" you are talking about, are you talking about compressor stall or wing stall? $\endgroup$ – SMS von der Tann Nov 28 '16 at 14:39
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    $\begingroup$ What exactly is the Falcon controlled descent technology that you mentioned? Are you asking if airliners could use rockets for emergency landings? $\endgroup$ – Pondlife Nov 28 '16 at 14:54
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    $\begingroup$ where would you fit the extra equipment required? who would pay for the extra cost caused by the extra weight? $\endgroup$ – Federico♦ Nov 28 '16 at 14:59
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    $\begingroup$ aviation.stackexchange.com/questions/11584/… $\endgroup$ – abelenky Nov 28 '16 at 15:57
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    $\begingroup$ Rockets are machines, and so are subject to failures. They also tend to carry a lot of rather explosive fuel: see for instance the recent SpaceX explosion, or the explosion of the Pepcon rocket fuel plant back in 1988. So it seems that putting emergency rockets on planes might easily cause more accidents than they prevent. $\endgroup$ – jamesqf Nov 28 '16 at 17:44
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They could but there really is no reason to do so. Most aircraft glide just fine if they lose all engine thrust and are perfectly controllable in such situations (provided they can actuate the control surfaces). As for the situation you propose there are a few issues with it,

First off, rocket fuel is not jet fuel and can't just be burned in the same way.

The JATO engines are a bit different than the rocket assist that Space-X is using (although the principal is similar). For takeoff the Jato engines help add to the totally available thrust and allow the plane to get off the ground in a shorter distance. The rockets are (I believe) single use and provide a very quick burst of thrust.

As for the loss of control this depends on what causes the loss of control and how the rockets are affixed to the airframe. In the case of the Alaska airlines flight you reference the jack screw forced the tail into a position and prevented it from moving, this put the plane in an unrecoverable dive that would only be exacerbated by rocket engines unless you could control the angle at which they were pointed. Again in the outlined case you would need to be able to counteract the full surface deflection of a control surface. In essence you would need the kind of thrust control that space ships have used over the years.

Now to answer the broad question of "could rocket thrusters be used to bring a disabled aircraft down softly" the short answer is yes. They could be added for such a task but the toll they take on the plane would make it a hard sell to the airlines. In short the use case is small and the added weight cuts into the profitability of the flight (you need a lot of jet fuel and heavy thrusters to pull this off). On top of all that the system would have to be built and certified for use, a task that should not be taken lightly. In the end you get a safety system that has a small use case and a big impact on the aircraft. Perhaps the best thing airplanes can learn from space craft landings is the use of parachutes.

The last and somewhat debatable point (common to all safety systems) is when do you actually turn it on? What is your definition of unrecoverable (yes this varies)? Cirrus teaches people to basically always pull the chute in an emergency. Are you going to teach pilots to to always trigger this rocket decent system even if the plane may be recoverable? What if you run out of fuel before getting to the ground and now you are to low to recover from the rocket assisted decent?

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Well, the idea isn't new. During the Iran Hostage Crisis of 1979, an secret rescue attempt codenamed Operation Credible Sport, which would have utilized a one-of-a-kind YMC-130 Hercules aircraft fitted with downward and forward firing JATO rockets, which were planned to allow the aircraft to land in a soccer stadium near where the hostages were being held. It crashed during a test flight on Oct 29, 1980 due both to equipment malfunction and flight crew mishandling. The project was scrapped shortly thereafter due to successful negotiations with Iran on the part of the Reagan Administration obtaining the release of the hostages.

As to whether this kind of a technology would ever be added onto a commercial aircraft, well the YMC-130 was partly a failure and partly a success. It was a failure in the sense that there was never a fully successful test flight resulting in a crash, but it was a success in the sense that the crew walked away from the accident, perhaps a prophetic picture of what would happed to a commercial airline outfitted as such.

I doubt the airlines would be interested in the system for the following reasons:

  • The system is going to add a lot of excess weight and drag onto an existing airframe or even one specifically designed for this - weight which is not paying its way on each flight and burning extra fuel to lug it around on each flight.

  • These systems also require maintenance and overhaul to work properly, adding additional costs.

  • This in an embryonic technology without a lot of flight time behind it and one disastrous flight test; not exactly a great selling point to airline executives.

  • As airline accidents already have over a 90% survivability at current time, such a system seems unwarranted for deployment into commercial aviation.

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For the fuel storage argument, the rockets could burn what is available in the tank without the need of auxiliary tank dedicated to them.

Fuel on board airplanes lacks the oxidizer that rockets need. Instead, jet engines suck in air.

What you're asking is adding huge rockets—with their oxidizer—that can match the plane's weight, a thrust-to-weight ratio that exceeds 1:1. Already airplanes have low thrust-to-weight ratios. You'd be building a very heavy inefficient plane that carries around dead-weight for most if not all its lifetime.

Why is lift larger than thrust?

While I'm sure you don't mean for a plane to land on its tail, instead sink down then arrest its descent in the final moment, poses a big problem. Slow flying (or sinking) planes get out of control and spin because of the big wings protruding either side.

For forward flight/glide, all jetliners already have more than one engine, that's the built-in redundancy right there.

Any emergency that results in control difficulties, won't be solved by arresting rockets, those depend on immense levels of controllability.

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