Los Angeles police officers fire tear gas into a Van Nuys apartment unit as they search for a reported second gunman after an LAPD helicopter was fired upon, forcing it to make an emergency landing. No second gunman was found. (Ringo H.W. Chiu, for The Times / April 24, 2011)

Jet fuel was pouring from the bullet hole when the Los Angeles Police Department helicopter struck by sniper fire Sunday in Van Nuys made an emergency landing, authorities said Monday.

The pilot "heard a loud thump outside the aircraft and took evasive action," said Robert Price, chief pilot for the police Air Support Division. "He knew the fuel tank had been hit - he could smell the fuel and some of it got on the windshield."

The names of the pilot and observer aboard the A-Star American-Eurocopter AS350 B2 were not released. Officials consider the two to be witnesses in a criminal investigation into the attempted murder of police officers.

Police arrested Danny Lopez, 18, after officers reportedly saw him aiming a rifle skyward in the 15700 block of Saticoy Street about 6 a.m. Officials said Monday that no other suspect is being sought.

Air Support Division officers said airborne police have been targeted by lasers, but "it's been a long time" since bullets were fired at the department's 19 helicopters, said Lt. Phil Smith of the helicopter unit.

"Gunfire directed at us, that's a surprise," Smith said. Helicopter crews know "there's a potential for it ending badly" when a craft is struck by bullets.

Smith said the crew involved in Sunday's emergency landing at Van Nuys Airport was back at work Monday. The helicopter was being checked for additional bullet damage, he said.

Although Price said he envisioned no change in protocol for police helicopters circling about 500 to 800 feet above crime scenes, Smith said the craft "may have to go a little higher and farther out" in the future.

Police try to keep at least two helicopters airborne at all times, and crews practice emergency auto-rotation landings every 90 days. Sunday's landing was done under full power, they said.