A Pan Am jet taking off with 136 people was forced into a steep climb to avoid a small plane mistakenly allowed onto the runway, and the aircraft came within 20 to 50 feet of each other, an official said Monday.

No one was injured in the incident Sunday at Logan International Airport.The Boeing 727 scraped its tail in the takeoff maneuver and had to return to the airport for examination, said Michael Ciccarelli, regional spokesman for the Federal Aviation Administration. The extent of the damage was not immediately known.