United Airlines Flight 389
|Date||August 16, 1965|
|Summary||Controlled Flight Into Terrain|
|Site||Lake Michigan, USA
|Aircraft type||Boeing 727-22|
United Airlines Flight 389 was a scheduled flight from LaGuardia Airport, New York City, New York, to O'Hare International Airport, Chicago, Illinois. On August 16, 1965, at approximately 21:21 EST, the Boeing 727 crashed into Lake Michigan 20 miles (32 km) east of Fort Sheridan, near Lake Forest, while descending from 35,000 feet mean sea level (MSL). All 30 people on board perished, including Clarence "Clancy" Sayen, the former president of the Air Line Pilots Association. There was no indication of any unusual problem prior to impact. United Airlines Flight 389 is still used as a JFK-SFO route using a Boeing 757-200.
A definitive cause was not determined by National Transportation Safety Board (NTSB) investigators. However, it was believed that the crash was most likely the result of the pilots misreading their three-pointer (3p) altimeters by 10,000 feet.
The flight was cleared to an altitude of 6,000 feet MSL by air traffic control (ATC), but the plane never leveled off at 6,000 feet. Instead, it continued its descent, at an uninterrupted rate of approximately 2,000 feet per minute, until it hit the waters of Lake Michigan, which is 577 feet MSL.
The control tower at O'Hare lost radio contact with the plane as it approached the western shore of Lake Michigan. A tower crewman at O'Hare said the pilot had just received landing instructions and had replied "Roger" when communication with the plane failed. Wallace Whigam, a lifeguard for the Chicago Park District, reported from the North Avenue Beach House that he had seen an orange flash on the horizon. Three seconds later, he reported, there was a "thundering roar." Other reports of the crash flooded police and Coast Guard from the North Side and North Shore.
The Coast Guard reported that skin divers had assembled at the North Shore Yacht Club in Highland Park, which was used as an informal search base. After a search of several hours there were no signs of survivors, though the area was kept ready in case any were found. Hours after the crash, members of the Civil Aeronautics Board (the predecessor to the NTSB) were on scene to begin investigating the accident.
The most likely explanation is the pilots thought they were descending through 16,000 feet MSL when they were actually descending through only 6,000 feet MSL. Time and radar-image analyses indicated the plane was already down to an altitude of between 1,000 and 2,500 feet MSL when it was again given the 6,000-foot (1,800 m) clearance limit. That final clearance was acknowledged by the captain, and was the last communication with ATC prior to impact with the water.
The captain of a 707 which was 30 miles (48 km) behind the accident flight stated their descent was in instrument conditions until they broke out of the cloud layer at about 8,000 to 10,000 feet and approximately 15 to 20 miles (24 to 32 km) east of the shoreline. The night visibility was "fuzzy and unclear", and lights on the shoreline were the only ones visible.
A study by the Naval Research Laboratory published in January 1965 found that, of four different designs of pilot altimeters, the 3p design was the one most prone to misreading by pilots. The study revealed that the 3p design was misread almost eight times more often than the best-designed of the four altimeters tested. It was also noted that it took the pilots considerably longer to decipher the correct reading of the 3p than with the other altimeters.
The NTSB estimated the plane was traveling at a speed of approximately 200 knots (230 mph) when it impacted the water. The investigation was hampered by the fact that the flight data recorder (FDR) was not recovered intact from the wreckage, which was in muddy water 250 feet (76 m) deep. Portions of the FDR were recovered, but the recording media was never found.
"The Board is unable to determine the reason for the aircraft not being leveled off at its assigned altitude of 6,000 feet."
The first proven case of a crash caused by a pilot misreading the altimeter by 10,000 feet was of a BEA Vickers Viscount outside Ayr, Scotland, on April 28, 1958. The second proven case was the 1958 Bristol Britannia 312 crash near Christchurch, Dorset, in the south of England, on December 24, 1958. While the former carried only a flight crew, all seven passengers and two of the crew members perished in the latter accident, and surviving crew members helped to pinpoint the cause.
- Iberia Airlines Flight 062 - another incident where altimeter misreading is suspected, but not proven
- 1958 BOAC Bristol Britannia crash
- Air safety
- List of unrecovered flight recorders
- NTSB Aircraft Accident Report
- NRL Report 6242, "Altimeter Display Evaluation, Final Report," January 26, 1965
- ICAO Accident Digest Circular 59-AN/54 (129-132)
- ICAO Accident Digest Circular 62-AN/57 (44-47)