Sometimes, it's a necessity. But regardless of whether or not you can get around taking your dog on a flight with you, it's a good idea to weigh all the options before booking them a flight; that includes being realistic about what can happen in a worst case scenario.
Some airlines allow small dogs to travel inside the plane with their owners. Larger dogs (those that don't fit comfortably in a carry-on sized bag) or those passengers on other airlines can be out of luck, however, and your canine companion could be designated as luggage.
Kennels and crates are often checked into the airline's care at the same time you check your suitcases. And those who have had baggage lost - or who have tried to bring back delicate items inside a suitcase - know just what horrors can befall luggage. The same is true for your dog. As careful as a handler may be, it's extremely easy for a crate or kennel to be tipped over, bounced around, or crushed during the chaos of loading or unloading a plane. And if a kennel is pushed or broken open, the likelihood that your dog will escape onto a busy runway or into a bustling, scary airport is high.
At one time, baggage was stored in compartments that weren't necessarily temperature controlled or airtight. While conditions are much more favorable to any animals that might be travelling in the cargo hold, weather conditions can still be a very real danger to flying dogs. Leaving from Phoenix? Your dog could be sitting in 120+ degree temperatures while waiting to be put on the plane. Have a layover in Minnesota? He could be sitting in the freezing cold. And remember, cabins and baggage areas only get pressurized once the plane is in the air, so sitting on the runway for two hours waiting for a gate is even worse for your dog.
Luggage sent to the wrong airport is a hassle for any traveler, and it's an equally possible nightmare when it comes to your dog. In the worst case scenario your dog could end up at a completely different destination, in an airport not equipped to deal with pets, or in an area where employees and handlers aren't even aware there's a dog.
For some airlines, breed is a concern. Short-nosed, flat-faced dogs like pugs aren't even allowed on some flights because of the difficulties they will undoubtedly have in breathing through the change in altitude and air pressure.
Instead of the cases of fatalities, illnesses and lost pets going down, many airline reports actually show an increase in the cases of a dog being injured or killed in flight.
So think carefully before taking your beloved dog on a plane with you, and if possible, make other arrangements.