At 16:52 PST, a Cessna 172N made an emergency landing at the El Monte airport after experiencing an in-flight cockpit fire. The aircraft was destroyed in the subsequent ground fire. The pilot was not injured; a passenger and airport employee were treated for smoke inhalation. The flight was a traffic aerial observation flight for a local radio station and originated at the Van Nuys airport. The pilot said the airplane was over a traffic accident about -mile from the El Monte Airport. The pilot was in the right seat and the reporter was in the left seat. The reporter switched the left door post-mounted map light to the on position, and a pop noise was heard. Almost immediately, flames shot out from both sides of the Royalite molding covering the left doorpost. The pilot reported that black smoke filled the cockpit. He removed his shirt and attempted to suppress the fire, but was unsuccessful. The reporter then moved to the back seat to escape the flames. The pilot declared an emergency and set up for a downwind landing on runway 1. By the time the airplane landed the flames had spread to the left side cockpit sidewall upholstery and the left side of the cockpit glareshield/instrument panel. As the airplane rolled to a stop, the reporter exited the right side door, followed immediately by the pilot.