Boeing 747 accident at Chicago, Illinois, 15 Feb 1979 (N467DA)

Accident narrative

About 0911 c.s.t. on February 15, 1979, a near collision occurred on the ground at O'Hare International Airport in Chicago, Illinois. Delta Air Lines Flight 349 was cleared to cross an active landing runway just as Flying Tiger Flight 74 was landing on it. To avoid a collision, the Flying Tiger captain veered his aircraft off the runway into the snow. The Boeing 747 was substantially damaged, but the Boeing 727 was not damaged, and there were no injuries to the occupants of either aircraft.

### The flights

Delta Air Lines Flight 349, a Boeing 727-200 (N467DA), was a scheduled passenger flight to Orlando, Florida. There were eight crewmembers, a cockpit jumpseat rider, and 106 passengers aboard.

Flying Tiger Flight 74, a Boeing 747-F (N804FT), was a scheduled cargo flight from Seattle-Tacoma to John F. Kennedy International Airport, New York, with a scheduled stop at O'Hare. It carried three flightcrew members and three nonrevenue passengers.

### The sequence of events

At 0906, the O'Hare outbound ground controller cleared Delta Flight 349 to taxi to runway 4R, instructing the flight to hold short of runway 9R.

Meanwhile, Flying Tiger Flight 74 was approaching the terminal area. After declining an approach to runway 9L due to weight restrictions, the captain accepted an immediate instrument landing system (ILS) approach to runway 9R. The flight was sequenced behind United Air Lines Flight 225, a DC-10, and ahead of Trans World Airlines Flight 291, a Boeing 727. The local controller advised that the runway 9R visual range (RVR) was 3,000 feet in the landing area and 6,000 feet in the rollout area.

At 0909:35, the United DC-10 landed. Flying Tiger Flight 74 was about 2 miles from the runway threshold. Ten seconds later, after the United aircraft turned onto a high-speed taxiway, the local controller cleared Flying Tiger Flight 74 to land.

At 0910:00, as Delta Flight 349 approached runway 9R on a parallel taxiway, the ground controller cleared the flight to cross the runway, transmitting, "...keep it moving, sir, and cross runway niner right..." The ground controller later stated he had checked his radar display, observed landing traffic, and assumed it was the next aircraft in the landing sequence.

Expecting to stop, the Delta captain had been taxiing slowly. After receiving the crossing clearance, both Delta pilots stated they looked toward the approach end of runway 9R but saw no traffic. The captain recalled a fog bank in the vicinity of the west end of the runway, estimating visibility to the west at about a half mile.

At 0910:05, Flying Tiger Flight 74 reported the approach lights in sight. The captain stated he first sighted the lights from 300 feet above ground level, describing atmospheric conditions similar to a "white-out." The aircraft landed about 2,400 feet down the runway, and the captain applied reverse thrust to three engines; the No. 4 reverser was placarded inoperative.

About this time, the Flying Tiger first officer called the captain's attention to the Delta Boeing 727 moving slowly onto the runway. At 0910:29, the Delta first officer sighted the Boeing 747 approaching from his right side and shouted a warning. At 0910:30, Flying Tiger Flight 74 transmitted on the local control frequency, "Hey, Delta stop." Because the two aircraft were on different radio frequencies, neither crew heard the other's clearances or warnings.

As the Delta aircraft moved further toward the runway center, the Flying Tiger captain steered his aircraft to the right. The Boeing 747 left the runway at about a 16-degree angle, passing immediately in front of the Delta aircraft at 0910:31. The Boeing 747 traveled 1,325 feet through 2 to 3 feet of snow, stopping about 100 feet south of the runway. The crew and passengers evacuated via the flightdeck slide chute. The Delta aircraft stopped momentarily, then taxied clear.

### What the investigation found

The Boeing 747 sustained substantial structural damage to its forward lower fuselage and inboard engine installations. The No. 2 engine separated from the aircraft, and both the right and left wing landing gear separated.

The investigation reviewed air traffic control procedures. The approach controller had sequenced Flying Tiger Flight 74 only 2 miles behind the preceding heavy aircraft, failing to comply with the 4-mile radar separation minimum required for wake vortex avoidance. When the local controller cleared the flight to land, he noted the less-than-required separation but did not issue a missed approach clearance.

A local tower directive authorized the ground controller to clear aircraft across an active runway without coordinating with the local controller, provided he visually scanned the runway and utilized radar displays to ensure no conflict. The Board concluded that the ground controller's clearance was the result of a failure to see the displayed radar target. The automated radar system was programmed to drop data tags for arriving aircraft 2 miles from the runway threshold, leaving only an asterisk symbol. The Board believed the ground controller failed to see the asterisked target of Flying Tiger Flight 74 and instead accepted a more conspicuously displayed target with a data tag—Trans World Airlines Flight 291, which was about 5.25 miles behind—as the next arrival.

The Board also conducted a cockpit visibility study. It determined that from a normal eye reference position, the Delta first officer could not have seen the Boeing 747 until about 4 seconds before the near collision, though this response time probably was sufficient to have stopped the aircraft. The Delta captain could not have seen the approaching aircraft from his position until 1 to 2 seconds before it passed. The Board noted that the predominant silver-gray fuselage of the Boeing 747 would have been inconspicuous against the dull overcast, and its landing lights were not illuminated.

### Probable cause

The National Transportation Safety Board determined that the probable cause of this accident was "the O'Hare outbound ground controller's issuance of a taxi clearance across runway 9R, which permitted Delta Flight 349 to move into a collision path with Flying Tiger Flight 74 and, further, the failure of the pilots of Delta Flight 349 to maintain a continuous vigil for landing traffic before entering an active runway. The improper clearance was the result of the ground controller's failure to see the displayed radar target of the landing aircraft."

Contributing to the accident were "the approach controller's failure to effect required spacing criteria between Flying Tiger Flight 74 and the preceding arrival aircraft and the local controller's failure to issue a missed approach clearance when he noted the less-than-required separation."