A team of 20 investigators from the Federal Aviation Administration yesterday began probing Delta Air Lines' pilot training program, looking for inadequacies that may have contributed to a series of five incidents ranging from a near-collision over the North Atlantic to a landing on the wrong runway in Boston.

Investigators will search Delta's files and training manuals in the effort, which the FAA calls a "special emphasis surveillance." The airline, the nation's fourth largest carrier, will assemble "profiles" of the incidents -- detailing pilots' ages, experience levels, training, and work schedules -- to determine if they contain a common element.

FAA spokesman Fred Farrar said the agency will be looking for flaws in Delta's training procedures. "Is it truly random?" he asked. "Is there something we can fix?"

The probe will investigate the landing of a Delta jet in Frankfort, Ky., about 20 miles from its destination in Lexington; a Delta landing on the wrong runway at Boston's Logan International Airport, just as an Eastern Airlines jet was preparing to cross the runway; a Delta pilot's attempt to take off on a runway in Nashville when another jet already was taking off from the other end; the inadvertent shutdown of a Boeing 767's engines by a Delta pilot taking off from Los Angeles; and the near-collision of a Delta L1011 and a Continental Airlines 747 over the North Atlantic, after the Delta pilot strayed 60 miles off course.

Delta announced it has begun two in-house investigations -- one to review pilot training and the other to review the string of recent incidents. The airline has 5,800 pilots.

Jim Ewing, Delta's chief spokesman, said all of the incidents involved senior pilots and none involved former Western Airlines pilots, who became Delta pilots after the two airlines merged April 1.

The FAA probe, which will take between three and six weeks, will concentrate on long-range navigation procedures, cockpit training and crew coordination. Sources close to the investigation of the near-collision over the Atlantic said they believe the Delta pilot may have entered incorrect coordinates into his navigation system, which could have misguided the plane.

Acting FAA chief Robert E. Whittington said in a statement that the agency has found no obvious pattern among the incidents, but he added that each involves human error, "and this is a matter of grave concern."

Investigators also added to the probe a new incident that occurred Monday 50 miles west of Oklahoma City. A Delta plane strayed several hundred feet above its assigned altitude and, in the words of the FAA, "conflicted" with a Southwest Airlines jetliner.

The two planes came within 700 feet of each other vertically and 1.9 miles horizontally. Both were being directed by air traffic controllers at the Fort Worth Air Route Traffic Control Center.

The airline's spate of bad luck included two Delta flights that were forced to return to Los Angeles International Airport yesterday because of mechanical problems. Neither involved pilot error, but an FAA spokesman said both incidents were serious.

A Boeing 737 bound for Mazatlan, Mexico, had to return after the crew discovered a malfunctioning control panel. A Boeing 727 headed for Salt Lake City lost cabin pressure because a door to the plane's galley was not properly closed.

Adding insult to injury, a Delta flight from Atlanta to Columbus, Ohio, was canceled when the crew found a monkey loose in the cargo hold.