For cellos, you may want to request or purchase an extra seat in the bulkhead area for your instrument. Or you can use a special cello shipping case and check your instrument. Be aware that no shipping case provides a guarantee against damage, but using one helps improve the odds that your instrument will survive the flight undamaged.
There are two types of shipping cases for cellos:
A 3 to 5-inch thick padded soft cover that fits around your normal case and often has wheels for easier transport. If the shipper drops the instrument, the thick foam will soften the blow. However, if the instrument is lying on the ground and something very large or heavy falls on top of it, the foam will be crushed and the cello may be damaged.
A very strong and heavy hard case that is used instead of the normal case. It offers more protection should something heavy fall on it. However, if the instrument is dropped, this type of case is more likely to transfer the blow to the cello because the padding inside is usually limited. Another disadvantage with this type of shipping case is that after arrival, you have to lug this heavy case around until you return home.