What happened
In September 2014, an ExpressJet Airlines Embraer EMB-145LR, operating as flight 4538 under instrument flight rules, departed from Grand Rapids, Michigan, bound for Newark Liberty International Airport in New Jersey. During the flight, the aircraft moved north of its intended path to bypass active thunderstorms and reached a cruising altitude of flight level 370.
At roughly 1915 Eastern Daylight Time, the aircraft entered a large thunderstorm cell. This encounter resulted in severe turbulence, which caused the flight crew to lose control of the plane. The aircraft underwent a rapid descent of about 4000 feet before the crew successfully stabilized the flight. The aircraft eventually reached Newark and landed without incident. There were no injuries to the 26 passengers or the 3 crew members on board, and the aircraft sustained no damage.
The investigation
The investigation focused on the aircraft's deviation from its flight path and the subsequent atmospheric conditions encountered during the flight. Investigators examined the sequence of events leading from the departure in Michigan through the encounter with the thunderstorm cell near London, Ontario.