An Air National Guard (search) pilot who accidentally fired on a New Jersey school during a nighttime training exercise was to blame for the incident, but poorly designed controls in the F-16 also played a role, the Air Force concluded Friday.

The report, obtained by The Associated Press, also disclosed there have been three other incidents this year in which an F-16 (search) pilot unintentionally fired during nighttime strafing missions. No one was hurt in any of the incidents.

The report called the Nov. 3 incident in New Jersey an "unfortunate and unintentional mistake." It said the pilot never intended to strafe the Little Egg Harbor Township Intermediate School (search), and it suggested computer software changes to the aircraft control systems to prevent another incident.

"The last thing he wanted to do, obviously, is have the gun fire and have rounds land off the range," Col. Brian Webster, commander of the 177th Fighter Wing of the New Jersey Air National Guard. "He simply got confused. He had the gun up and armed."

He said the software upgrade being installed on 600 older F-16s nationwide will make it impossible to use the same trigger mechanism to activate the aircraft's laser target marker and fire its 20mm cannon.

The Air Force board that investigated the New Jersey accident recommended the change.

"In my opinion, using the same trigger for both laser marking and firing the aircraft's gun significantly increases the risk of human error and an unintentional gun discharge," the board's head, Col. Kevin W. Bradley, said in the report.

The other accidental firing incidents occurred at the Adirondack firing range in upstate New York and at two ranges in Western states, Webster said; none of them involved projectiles landing outside the range.

The pilot in the New Jersey incident was identified as Maj. Roberto Balzano of the 113th Wing of the District of Columbia National Guard, based at Andrews Air Force Base in Maryland. The report said his commander will determine if any punitive or administrative action should be taken, and whether any retraining is necessary.

Balzano has more than 2,000 hours of experience flying planes, 975 hours of which were in the F-16s.

Balzano, referred to in the report as the "mishap pilot" or MP, was verifying his aircraft position in relation to his intended ground targets on the Warren Grove range, about 30 miles north of Atlantic City. The school is about four miles from the range.

"Unfortunately, the MP forgot that his aircraft's air-to-ground gun mode was selected and armed ready to fire. The MP immediately realized his error when the aircraft gun's discharged," the report said.

The accident happened as Balzano was flying at approximately 7,000 feet. Twenty-seven rounds of inert 20mm ammunition were discharged. Eight of the 2-inch lead rounds punched through the school's roof, knocking down ceiling tiles. At least one round struck a child's desk, and others scuffed the asphalt in the parking lot.

Balzano immediately told the control tower something had gone wrong, scrapped his mission and returned to Andrews.