Packing a bicycle for a flight

There are several schools of thought on how to pack a bicycle for a flight. Some like to leave it unpacked so that the baggage handlers will see it's a bike and will treat it gently. Others are convinced that only a hard shell case with steel bracing will do the job. Most of the cyclists take the middle way and put the bicycle in a cardboard box. So let us first start with:

Recipe for packing a bicycle in a bike box

Ingredients:
- 1 road bicycle, size 622 (or 700c) wheels, frame of the size L (or 58), drop bar.
- 1 cardboard box of dimensions 138x78x20 cm.
- several pieces of cardboard (a middle sized cardboard box will do).
- 1 spacer for the fork (or cardboard).
- 1 roll of packaging tape.
- 2 meters of duckt tape.
- 2 or 4 plastic bottles.
- Allen keys 4, 5 and 6 mm.
- 15 mm pedal spanner.
- scissors.
- 1 large beer.

Procedure:

1. Put the beer in the fridge.
2. Tape the bottom of the box with packaging tape, from inside and outside.
3. Reinforce the carrying openings of the box with cardboard from the inside.
4. Shift the chain to the largest rear cog and largest front ring.
5. Put one plastic water bottle in a bottle cage.
6. Unscrew the pedals.
7. Fix one crank arm by taping it to the seat tube with duckt tape. The other crank arm should point down below the front rings to protect them.
8. Remove the seat and fasten back the seat clamp.
9. Deflate the tires slightly. The rear one a bit more then the front one.
10. Lower the rear wheel a bit below the dropout and move the wheel toward the seat tube. Tighten the rear Quick Release. This will give you some more room to fit the bike in the box. You may not need to do this if the box is long enough.
11. Cut the bottom of plastic bottles and protect the rear axle and the rear derailleur with it. This is done in order to prevent the axle puncturing the box and as a protection of rear derailleur. If you have only 2 bottles, cut them in quarters. 
12. Unscrew the stem-steerer bolts and turn the handlebar for 90 degrees in line with the bike.
13. Fasten the stem-steerer bolts back.
14. Turn the bike upside down.
15. Remove the front wheel and remove the front quick release axle.
16. Put a spacer in fork dropouts. You can use a rolled piece of cardboard.
17. Protect the front wheel axle with plastic bottles.
18. Put the bicycle (without the front wheel) in a box.
19. Unscrew the stem-handlebar bolts and remove the handlebar.
20. Screw the stem-handlebar bolts back in.
21. Put the front wheel in the box so that it fits somewhere between the fork and the seat tube.
22. Put the handlebar in the box.
23. Put additional pieces of cardboard between the wheel axles and box sides, and between the front wheel and bicycle frame.
24. From a couple of pieces of cardboard a bit wider then the box width make rolls and put them in the box as spacers. This is not a crucial step, but will give you some protection against squashing the box. 
25. Put the saddle, the pedals and front QR axle into the box and fix them to the bike or the rack.
26. If you have anything else to put in a box, do it now.
27. Shake the box and look for any loose parts. Everything should fit tightly without moving.
28. Close the box and seal it with packaging tape.
29. Have a beer.

Time required: 2 hours.

If you have smaller bike or wheels (MTB especially) and flat handlebar you can use a smaller box. If the box is too small, you'll have to take the rear wheel off too: in this case the procedure might be considerably different.

Other options

Of course, the cardboard box is not the only way to pack the bike for a flight. Other options are:

1. Leave the bike unpacked, just turn the handlebar, lower the seat, deflate the tires and remove the pedals. There is an ongoing debate whether by doing so your chances of getting your bike damaged are increased or decreased.
2. Dismantle the bike and put it in a hard shell travel case. This would certainly be the preferred method if you have somewhere to leave the case upon your arrival.
3. After the procedure as in 1, put a minimal protection made of pieces of cardboard or pieces ob plastic bottles on the sensitive parts: shifters and derailleur. Something like this.
4. After the procedure as in 1, wrap the bike in plastic. You can use a roll of food wrapping plastic. A roll of 30cm x 50m should do. The result looks like this.

Which procedure to use might depend on the policy of the airline company and whether you are starting the tour or flying back. I prefer to start the tour by packing the bike in a box as explained and my preferred option for a return trip is to wrap the bike in food-wrapping plastic. This allows me to cycle to the airport with minimal packaging material and without hassles of finding a box or transportation, preparing the bike and wrapping is quite easy and fast (half an hour) and attracts lot of interested attention at the airport. It also complies with rules of some companies that the bike has to be packaged (to avoid damage to other baggage).

On return trips I usually improvise. More so as I like to cycle all the way to the airport.
This is hardly a school example of the proper packaging of a bike for the flight, but, weighing less then 10 kg it was free of charge on the plane and arrived unscratched to destination after 3 connecting flights.
Ingredients/tools required: a roll of scotch tape, a piece of cardboard and a razor blade.
Pedals and seat were in my hand-luggage, tools & tent spikes (not allowed as hand-luggage) were taped to the rack .

Improvisation can save you some money on train (or bus) trips too. As an example, I can tell you my experience on trains Dali-Kunming (seater) and Kunming-Chengdu (hard sleeper) in China. I bought the biggest bag I could find on the market, disassembled the bike and put it (stuffed it really) in the bag and carried it on the train. The bag was too small even only for the frame and rear wheel, I carried second wheel in the other hand, but nobody in the station or in the train said anything. In the seater I put the bag in the place between compartments and in the sleeper under the bed. Everything went smoothly, except that my arm grew few cm longer after carrying the bag around the stations. See the picture of the bike/bag below.

This is hardly a school example of proper packaging of a bike,
but it was free of charge on the train.