Are there any known laws of nature, which don't allow the existence of an animal with following characteristics?

1. Can fly to the altitudes of modern airliners (around 10 000 meters or 32808 ft).
2. One of the sources of thrust are organic jets or rocket engines (details see below).
3. The animal can carry up to three passengers (about 240 kilograms, 529 pounds).
4. The animal can fly up to 1000 kilometers (621 miles) using his own thrust source (that is, not just gliding or using the wind).

Regarding organic jet engine: There is at least one animal, which produces organic, flammable material - cows generate flammable methane. So, theoretically, an animal could have a combustion chamber in his body, where the flammable gas could be concentrated.

The next thing it needs is some form of nozzle, from which the gas would escape and it must have varying shape, controllable by the animal. Several animals can control the shape of their bodily openings, so it could be possible.

Finally, it needs a spark so that the flammable gas actually starts to burn, but that's easy - as stated in the requirements there is at least one pilot, who could activate a contraption, which generates a spark close to the nozzle.

I imagine that the animal can gain low altitude using wings (one of potentially many thrust sources), then the animal starts to generate flammable gas at the command of the pilot (we train dogs and horses, why not this fictious animal?) and the moment it opens the nozzle, pilot fires the ignition.

Here we go: A VTOL-capable (vertical take-off and landing), jet-powered dragon with at least two power sources (wings, jets - i. e. it is fail-safe).

Notes:

* I say *animal* on purpose - because of mental inertia I'm thinking about a dragon, but there may be other animals, which can fly with jets.
* There are some military fighter jets with [variable sweep wings](http://en.wikipedia.org/wiki/Variable-sweep_wing) that an animal could achieve easily (real birds do that all the time).
* An interesting variation would be an organic liquid-fuel rocket engine. Unfortunately, I know too little about rocketry to imagine how it work in an animal. Ideas in this direction are welcome.