>> during periods of growth you see airlines are usually pressed to try to put new people in service to -- bring in new aircraft. and all of that actually puts a little bit more risk in the system. >> reporter: and there is another risk, even now. >> you have to be careful not to assume that the battle is over for aviation safety. it is not. >> reporter: accidents happen in an instant. it takes work to ensure safe skies stay that way. lisa stark, abc news, washington. now to the deepening medical mystery over a bacteria linked to a deadly illness in infants. an oklahoma baby is now the third infant this month sickened by this bacteria that is sometimes associated with powdered infant formula. a baby in missouri died. and a chicago area baby went to the hospital and did make a recovery. many stores though have pulled enfamil powdered formula. as a precaution. the oklahoma baby was not given that enfamil formula.