The accident was attributed to confirmation bias which prompted the flight crew to continue descending even though they could not see the runway due to snow; poor decision-making by the captain, fatigue of the first officer, and problems with the airport's instrument landing system were identified as contributing factors.

The captain was 40 years old and joined CommutAir in March 2013 before working for another air carrier in November 2015, then returned in May 2016.

[1]: 13–14 Flight 4933 departed from Newark Liberty International Airport around 10:04 Eastern Standard Time (EST) (14:04 UTC).

At 11:01 EST, Boston Air Route Traffic Control Center cleared the flight for an instrument landing system (ILS) approach to runway 1.

Instrument meteorological conditions (IMC) prevailed at the airfield, with low ceilings, fog, and blowing snow.

At 11:28 EST, as the aircraft descended through 200 ft (61 m) AGL, the minimum decision height for the approach, the captain called out "runway in sight twelve o'clock."

The NTSB concluded that the probable cause of the accident was confirmation bias which prompted the crew to continue descending even though they had not positively identified the runway.

[1]: 1–5 Around the time of the first approach, the Automatic Weather Observation System (AWOS) at the airport was reporting wind from 060° at 4 kn (4.6 mph; 7.4 km/h) and visibility of 0.50 mi (0.80 km) in moderate snow and freezing fog.

He had been recently suffering from the flu and had lost sleep, and had made only limited and inconsistent use of his prescribed continuous positive airway pressure machine for several days leading to the accident.

While she had been a de Havilland Canada DHC-8 first officer with CommutAir, she had received a disciplinary letter and been subject to nine months of monitoring before being allowed to pursue captain upgrade training.