You've learned to carry him without worrying that he'll break, and you know him well enough to anticipate his needs. Flying with a baby is never carefree, but once he's 3 months old, he'll probably make a fairly peaceful traveling companion. Plan ahead so you'll have everything he needs: Children this young still require your constant protection and comfort, even at 30,000 feet.
Add Security Time
Getting through airport security with a 3-month-old and all his gear takes time. Before you go through the screening area, remove any items from the stroller pockets. Take off your coat or any extra layers that security agents would make you remove, and slip your shoes off and into a carry-on while you sit at a bench outside the security checkpoint. You'll run everything but yourself and the baby through the X-ray machine, unless you have a stroller or other item that won't fold down to fit. You'll carry your baby through the metal detector. Tell the security agent if you're carrying milk or formula, since it needs to be screened by hand.
Rely on the Kindness of Strangers -- Sometimes
Sympathetic strangers could make your trip smoother, especially airline employees. With baby in arm, ask the ticket agent if you could be moved into an empty row. At the gate, inquire whether any first-class upgrades are available; an agent might take pity on you. If you didn't book a seat for your baby, a gate agent might move you next to an empty seat anyway. Most airlines don't require this for children younger than 2 years old, but the Federal Aviation Administration does recommend your baby be buckled into a car seat in his own chair. Ask fellow passengers for help placing your bags in the overhead compartment, but if anyone gets too close to your little one, say apologetically, "He's actually just getting over a cold, so the doctor says everyone needs to keep their distance."
Focus on Baby's Ears
Those delicious little baby ears can cause a small baby plenty of discomfort on a plane. Changing cabin pressure during takeoff and landing could make him cry in pain, though not all babies experience ear pain during flight. As you begin takeoff and descent, discreetly cover yourself and breastfeed, or give him a bottle or pacifier to suck. This motion should keep ear pain at bay. If he's asleep during changes in pressure, let him sleep. Consider too that the chaos of an airport and the noises on a moving plane can be frightening for a baby. HealthyChildren.org suggests loosely placing cotton balls in his ears to block out the noise. Pulling a knitted cap down over his ears might also help.
Keep Your Baby Entertained
At 3 months old, he's alert and aware enough to enjoy stimulation. Pack a few simple, quiet toys like plastic rings or soft baby books. Rattles and squeaky toys are best left in your suitcase for now, since they'll disturb your neighbors. You can also use texture to keep him engaged, says BabyCenter.com. Bring some scraps of fabric with fuzzy, silky or bumpy textures with you, or pull a clean sock or shirt from his bag in a pinch. Run the fabric lightly over his skin, alternating caresses from your fingertips, to keep him smiling and soothed during a long flight.
Stick to Baby's Schedule
Three months old is the age at which your baby's habits start to be predictable, so take advantage of that and don't try to adjust his routine to fit the plane's schedule. If he's dozing off when the plane is loading, rock him outside the gate for as long as possible in hopes he'll be sound asleep before you have to board. Onboard, help him fall asleep by walking him in the aisle before takeoff or holding him in a sling across your body. His feeding schedule should be consistent, too. If you're crossing time zones, set an alarm to remind you when it's time for him to eat and take any medication. The Transportation Security Administration allows you to bring any milk or formula through security checkpoints; pack extra in your carry-on in case the flight is delayed or he develops crankiness that only milk will soothe.
Make Diaper Changing Easy
Change your baby's diaper just before takeoff to minimize in-air stress. When he needs to be changed on the plane, you might get lucky and discover the bathroom includes a changing table. In case it doesn't, bring a portable changing pad to lay down on the closed toilet lid. Remove most of his clothing at your seat so you're not struggling with it in the small bathroom. You might also change a wet diaper at your seat if you have a traveling companion next to you. Pull up the arm rest and lay your baby over both your laps. Cover the baby's bottom half with a blanket while you work.