A United Airlines flight from Houston to Seattle was forced to make an emergency landing in Idaho, when the pilot apparently had a heart attack.

The captain of United Airlines flight 1603 has died after he fell ill in the cockpit and his plane made an emergency landing in Boise. The cause of death and the captain’s name have not been made public, but a Boise airport spokeswoman said that he apparently suffered a heart attack on the plane, according to the Associated Press .

KIRO reported that after a crew member called for a doctor, two passengers attended to the captain. An off-duty United pilot aboard the plane helped land the plane safely about 8 p.m. Thursday in Boise. Passengers transferred to another plane and arrived in Seattle just after midnight.

The plane, a Boeing 737, was carrying 161 passengers and six crew.