On the 23rd of June, 1950, Northwest Orient Airlines Flight 2501 was flying from New York’s La Guardia airport to Seattle Washington when it disappeared into the night.

Northwest Airlines Corp was a US airline, which was founded in 1926 primarily to carry US mail. They began carrying passengers within the first year and began offering international routes the year after. In 1931, the airline sponsored a pioneering test flight to Japan via Alaska to scout out the Great Circle route. After the second world war, Northwest established a hub at Tokyo and the first direct service between the United States and Japan using a Douglas DC-4 airliner. As a result, they began to advertise themselves as Northwest Orient Airlines.

The airline was merged into Delta Air Lines in 2008. Northwest continued to operate under its own brand until 2010.

The aircraft for flight 2501 was a DC-4 which had been manufactured in 1943. It was originally operated by the United States Air Force and then by a Venezuelan postal operation before being purchased by Northwest in 1947. The end of the war meant that many surplus aircraft were sold to fledgling commercial airlines. It was used for a cargo service initially but in 1950, one month before the crash, it was converted to a 55-passenger cargo-coach aircraft.

The DC-4 was developed by Douglas, after United Airlines worked with them on the prototype of a four-engine long-range airliner. The DC-4E (E for experimental) was flight tested in 1939. It was three times the size of the DC-3 and could potentially fly nonstop from Chicago to San Francisco. The DC-4E never flew commercially but led the way for the smaller and simpler DC-4.

Flight 2501 was one of the DC-4 routes, a transcontinental service from New York City to Seattle.

The aircraft was in good repair and all of the maintenance records were in order. The flight crew who had flown the aircraft to La Guardia reported it as “mechanically okay” before going off shift.

The captain of flight 2501 was 35 years old. He qualified on the Milwaukee–New York segment in 1945 and had flown the route continuously over the following five years.

All times are given as Central Standard, which was the time zone for the believed accident location.

At 15:45 that day, Northwest released a special thunderstorm forecast.

Scattered thunderstorms along and east of the cold front, bases at 3,000 to 4,000 feet, tops 30,000 to 40,000 feet with moderate to severe turbulence at all levels in the thunderstorm and moderate turbulence below thunderstorms, advising flights below 10,000 feet to proceed with caution in the frontal zone, anticipating the activity to be at its peak between the hours of 2230 of the 23rd and 0400 of the 24th EST with possible squall line development ahead of the front during the evening.

The flight crew arrived at the Northwest Flight Control Office at about 18:00, an hour before their scheduled departure. They discussed the weather situation with the dispatcher and examined the hourly sequence reports.

The forecast was for thunderstorms in the Detroit-Minneapolis area, with moderate-to-severe turbulence above 10,000 feet and light-to-moderate turbulence below 10,000 feet. There was also a risk of a squall line developing: a line of thunderstorms that forms along or ahead of a cold front. A squall line means heavy rain, hail, lightning, strong winds and even tornadoes.

The captain and the dispatcher decided on a cruising altitude of 4,000 feet, which seems terribly low for a trans-continental flight by today’s standards. The flight route had them stopping over at Minneapolis, Minnesota and at Spokane, Washington before continuing direct to their destination of Seattle, Washington.

At 18:45, Northwest issued a new forecast, but the New York dispatcher didn’t receive it until after the flight crew of flight 2501 had left to check the aircraft. The 18:45 forecast predicted better weather than the 15:45 forecast, so the dispatcher did not advise the flight crew of the update.

The captain requested an altitude of 4,000 for the initial routing to Minneapolis but Air Traffic Control were not able to approve it, as they had other traffic assigned to that level. The final flight plan had a cruising altitude of 6,000 feet to Minneapolis.

The pre-flight check was normal and there’s no reason to think that there was anything wrong with the aircraft.

Flight 2501 departed La Guardia airport at 19:31 that evening with two flight crew and one cabin crew member. There were 55 passengers on board, including two families travelling with their children and three pregnant women. One passenger was so late, he almost missed the flight. The cabin crew member had already closed the door and had to open it again to let him on. She then passed out pieces of Wrigley’s Doublemint chewing gum before take off.

At 21:33 the Weather Bureau issued a regional forecast for the period 22:00 to the following morning at 10:00. This forecast predicted widespread thunderstorm activity and described the development of a squall line extending from southern Wisconsin eastward into lower Michigan and moving south. The southern edge of the squall line was located west of Benton Harbor.

Regional forecasts were not routinely broadcast and the Flight Advisory Weather Service man did not ask Air Traffic Control to warn flights about the squall line. Although the controllers had the information available, they did not think to do so either. The meteorologist at Northwest was not convinced that the squall line prediction was accurate and so no one at Northwest advised the flight crew of the forecast.

Flight 2501 flew over Cleveland, Ohio at 21:49. The flight crew again requested a cruising altitude of 4,000 feet, which was approved. Forty minutes later, Air Traffic Control asked them to descend to 3,500 feet.

An eastbound aircraft at 5,000 feet was experiencing severe turbulence over Lake Michigan and was struggling to maintain its assigned altitude. Air Traffic Control estimated that the two aircraft would pass each other around Battle Creek, Michigan and the controller was concerned that 1,000 feet separation wouldn’t be enough because of the turbulence.

At 22:51, Flight 2501 was flying over Battle Creek at 3,500 feet and reported that they expected to be over Milwaukee at 23:37. The radio operator incorrectly copied this down as 23:27.

At 23:13, the flight crew requested a cruising altitude of 2,500 feet. They didn’t say why, nor did they declare an emergency. Air Traffic Control declined the request as there was other traffic at that level.

The flight crew acknowledged that the descent was not approved and the flight continued at 3,500 feet.

This was the last communication from the flight.

On the other side of Lake Michigan, Northwest Radio at Milwaukee became concerned. It was 23:37, which was actually when the aircraft was expected to overfly Milwaukee and check in. However, according to his notes, he expected Flight 2501 to fly over at 23:27. He contacted both Northwest and Air Traffic Control to say that the flight was ten minutes late. The mistake seems almost like foreshadowing: the aircraft was already lost.

Ten minutes later, Northwest Radio still had not heard from the flight. Hoping that this was a communications failure, the controller broadcast that the flight should circle the range station at Madison, Wisconsin if its radio transmitter was inoperative.

Meanwhile, all CAA radio stations in the Chicago-Minneapolis area attempted to contact the flight on all frequencies.

Northwest contacted Chicago Air Traffic Control who altered the air-sea rescue facilities in the area at 23:58. Responders included the Air Force, Navy, Coast Guard as well as the state police of Illinois, Michigan, Wisconsin and Indiana.

By dawn, it was time to face facts: no word was heard from the aircraft crew and, if they’d still been flying, the fuel supply would have been exhausted. The aircraft must have crashed.

Search and rescue operations started searching foggy Lake Michigan as soon as the sun rose.

The New York Times reported (Milwaukee, June 25, 1950)

A Northwest Airlines DC-4 airplane with fifty-eight persons aboard, last reported over Lake Michigan early today, was still missing tonight after hundreds of planes and boats had worked to trace the craft or any survivors. All air and surface craft suspended search operations off Milwaukee at nightfall except the Coast Guard cutter Woodbine. The airplane, a four-engine ‘air coach’ bound from New York to Minneapolis and Seattle, was last heard from at 1:13 o’clock this morning, New York Time, when it reported that it was over Lake Michigan, having crossed the eastern shore line near South Haven, Mich. The craft was due over Milwaukee at 1:27 A.M. and at Minneapolis at 3.23 A.M. If all aboard are lost, the crash will be the most disastrous in the history of American commercial aviation. The plane carried a capacity load of fifty-five passengers and a crew of three, headed by Capt. Robert Lind, 35 years old, of Hopkins, Minn. In Minneapolis, Northwest Airlines said the craft was ‘presumed to be down,’ and that they were beginning notification of relatives of passengers. In his last report, Captain Lind requested permission to descend from 3,500 to 2,500 feet because of a severe electrical storm which was lashing the lake with high velocity winds. Permission to descend was denied by the Civil Aeronautic Authority because there was too much traffic at the lower altitude.

They searched until sunset but there was no sign of the aircraft.

The following morning, the search and rescue operation was expanded to include underwater searches. They loaded the boats with sonar equipment and sent divers down where strong sonar contacts were made. The lake was 150 feet deep in these locations. The lake bottom was covered by a layer of silt and mud estimated to be 30 to 40 feet deep. Visibility was less than eight inches. Everyone knew that the chances that they would find the aircraft this was was slight, but they continued anyway.

The entire area was also dragged with grapnel hooks in the hopes of pulling something to the surface, to no avail.

That evening, after 11 hours of searching, a US coast guard cutter discovered an oil slick on Lake Michigan about 18 miles north-northwest of Benton Harbor, the southern edge of the squall the night of the accident. Meteorological reports confirmed that a squall line was located there at the time that the aircraft was believed to have crashed.

The US coast guard also found the aircraft log book floating in the water. Further floating fragments was found in the area but they could not find the aircraft wreckage.

They scoured the lake and the surrounding areas for another day with no further results. After four days, the Navy suspended their search because of the difficult conditions. The Coast Guard and aircraft flying in that area continued to watch for any sign of the missing aircraft but the official search was over.

The only pieces of the aircraft which were recovered were fragments which could float free: foam rubber cushions, arm rests, clothing, blankets, pillows, pieces of luggage, a fuel tank float, cabin lining, plywood flooring and other wooden parts.

There was no sign of fire on any of the debris recovered. The cushions and arm rests were shredded from the impact, which means that the aircraft must have struck the water at high speed.

Body parts began to wash up on the shore. Some were described as “shredded”. Coast Guard officials initially believed that there must have been a terrible mid-air explosion to disintegrate the bodies so badly.

Soon, South Beach, popular with tourists, was forced to close because of the large number of body parts that washed in. Years later, two unmarked grave sites were identified which are believed to hold the remains of the flight-crash victims which washed to shore.

They were buried quickly and quietly as only small pieces were found, no intact bodies. One is a mass grave in a cemetery near St Joseph and the other at Lakeview Cemetery in South Haven. Both sites now have markers in the memory of the victims.

The only debris offering any information about the flight was a plywood oxygen bottle support bracket. The bracket had been installed on the forward left side of the fuselage, which meant that the impact force which ripped it off must have been forward, downward and to the left.

The Tribune quoted an unknown source from Douglas Aircraft Company, who speculated that perhaps the aircraft had turned onto its back. He said there were eight cases of this happening in high winds; however usually the flight crew usually had enough height to recover. As Flight 2501 was only at 3,500 feet, they had no chance.

Flights that crossed the southern Lake Michigan area shortly before and after the aircraft disappeared reported moderate-to-severe turbulence and frequent lightning (both cloud-to-cloud and cloud-to-ground). Several flights flew around the storm by flying to the south. Three flights turned back, refusing to carry on into the severe turbulence at the edge of the storm. One of the pilots reported that he couldn’t fly over the storm because it extended over 30,000 feet.

In 1950, this was the deadliest commercial airliner accident that the United States had ever experienced. The Civil Aeronautics Board, who was in charge of the investigation, could not determine a probable cause.

The mystery continues to this day. The plane struck the water with considerable force: that’s all that we know. It’s possible that there was a mechanical failure mid-flight, but the aircraft appeared to be in good condition and normally the flight crew would have reported as soon as they realised there were any issues.

Over 60 years later, the aircraft has still not been found.

The Michigan Shipwreck Research Associates has searched Lake Michigan for the aircraft wreckage every year for over a decade. Even if they find the wreckage, they won’t find the “black box,” in 1950 commercial aircraft did not carry them. They are most likely to salvage the four massive 14-cylinder engines, if anything at all.

We’re unlikely to ever understand exactly what happened that night but at least it would offer some closure to what happened to the aircraft.

CAB Accident Investigation Report, Docket SA-215, File 1-0081 can be found online at United States Department of Transportation Library under Investigations of Aircraft Accidents 1934 – 1965.