CNN WIRE -- What's known about recent aviation incidents

A series of aviation incidents now under investigation highlights concerns for travelers as summer travel ramps up and the United States marks its 250th anniversary. CNN reports that the TSA expects to screen nearly 18.7 million passengers at U.S. airport security checkpoints during the Fourth of July weekend, June 30 to July 6. The incidents include an Air Canada flight where a pilot faced a medical emergency while en route to Halifax from Newark; operated by PAL Airlines, the plane diverted to Boston Logan International Airport. The airline said the captain experienced a medical issue and was removed from the flight deck per safety protocols, and an emergency landing was carried out after the first officer took over. Another incident described involves a Cessna 208 Caravan making an emergency crash landing in rural Alaska, captured by a passenger on Monday. A separate case also references two passenger jets that nearly collided in Boston. Aviation safety expert Ed Pierson said investigators should assess what happened and apply fixes to prevent recurrence.