The captain of a commuter plane that crashed last December in Minnesota was an angry man who deliberately jostled passengers to spite his employer and sometimes bullied or hit his copilots, colleagues told investigators.

Marvin Falitz also failed semiannual proficiency checks three times in the past five years, according to reports released Friday by the National Transportation Safety Board.

The twin-engine Jetstream 31 -- Northwest Airlink Flight 5719 -- crashed near Hibbing, Minn., Dec. 1, killing all 18 people on board. The plane was operated by Express II, a commuter carrier affiliated with Northwest Airlines.

Falitz was in a bad mood the day of the accident because he was supposed to fly the next day, his day off, the reports revealed.

Speculation about the cause initially focused on the icy weather, but the reports released Friday indicate investigators are focusing on performance of the crew. There were suggestions in the report that copilots might have been reluctant to challenge Falitz if he made a mistake.

The plane had gone into a sharp dive, apparently to avoid icing, shortly before it leveled off, clipped a tree and crashed into a hillside. The steep descent was a common practice among Express II pilots in icy conditions, investigators found. Ice can cause a plane to lose lift.

Falitz had a reputation for following company procedures and being meticulous with flight check lists, according to investigators.

But three junior pilots, known as first officers, said he was sometimes "deliberately rough on the flight controls, causing the passengers to receive a rough ride," according to the NTSB reports.

Falitz told them that was "his way of getting at the company," Express II.

Some of the pilots also said "that they thought that Captain Falitz was angry with them but after flying with him for awhile, realized that he was angry with the company."

Express II's chief pilot told investigators he kept an eye on Falitz, whom he described as competent but "intimidating and provocative" with colleagues.

On one flight, Falitz repeatedly punched his copilot in the headset for making mistakes, according to the reports.

There was no indication of friction between Falitz and his first officer, Chad Erickson, 25, on the flight from Minneapolis-St. Paul in the transcript of the plane's cockpit voice recorder that was released Friday.

Before they took off, however, a ground agent said Falitz angrily criticized Erickson for an improper procedure on an earlier flight that day. The agent said he had "never seen {Falitz} act like this before."

"I did hear about his not getting along with employees," Warren Wilkinson, a spokesman for Memphis-based Phoenix Airline Services, Express II's parent company, said Friday. "But the cockpit voice recorder showed no abnormalities."

Falitz was "well-known and well-liked" by colleagues in his union, said Paul Omodt, a spokesman for the Northwest Master Executive Council. He was considered a "very easygoing, friendly guy," Omodt said. Omodt said he did not know Falitz personally.

Falitz failed pilot proficiency checks in May 1993, and in 1992 and 1988. He passed the tests after additional training. His last proficiency check, which he passed on the first try, was in November.

It is uncommon for pilots to fail the checks, said Hop Potter, a staff specialist in air carrier training for the Federal Aviation Administration.

The safety board should finish its investigation by the end of the summer, spokesman Alan Pollock said.