65 Years ago today: On 23 August 1954 a KLM DC-6 crashed into the North Sea while approaching Amsterdam, killing all 21 occupants.

Date:Monday 23 August 1954
Time:ca 11:30
Type: Douglas DC-6B
Operator:KLM Royal Dutch Airlines
Registration:PH-DFO
C/n / msn:43556/257
First flight:1952
Total airframe hrs:6308
Engines:Pratt & Whitney R-2800
Crew:Fatalities: 9 / Occupants: 9
Passengers:Fatalities: 12 / Occupants: 12
Total:Fatalities: 21 / Occupants: 21
Aircraft damage:Damaged beyond repair
Location:North Sea, 37km N Dutch coast (   Netherlands)
Phase:En route (ENR)
Nature:International Scheduled Passenger
Departure airport:Shannon Airport (SNN/EINN), Ireland
Destination airport:Amsterdam-Schiphol International Airport (AMS/EHAM), Netherlands

Narrative:
KLM Douglas DC-6 PH-DFO (named “Willem Bontekoe”) departed New York on 22 August for a flight to Amsterdam with an en-route stop at Shannon. The aircraft departed Shannon at 09:29 GMT for the last leg of the flight. After almost two hours the crew contacted Amsterdam and reported crossing the Netherlands FIR boundary. Three minutes later they contacted Amsterdam Area Control Centre reporting that they were starting the descent for Amsterdam, heading for the Spykerboor beacon. Estimated arrival time over the Spykerboor beacon was 11:37. The flight was then cleared to approach this beacon at 5500 feet or above, later amended to 4500 feet and 3500 feet or above. At 11:35 Amsterdam Area Control Centre cleared the flight to descend to 2500 feet but no answer was received. After an extensive search, hampered by low clouds, showers and heavy seas, floating debris was found at 16:10, off the Dutch coast near Bergen.
Witnesses on the ground reported having heard the flight pass overhead near Egmond (where Airway ‘Green 2’ crosses the coast. Other witnesses also reported seeing the aircraft at 12:01 when it passed overhead at a low altitude heading back for the sea.
Salvage work was stopped on November 25, when 45-50% of the aircraft had been brought ashore

Probable Cause:

PROBABLE CAUSE: “A number of hypotheses as to the cause of the accident were developed. Some possibilities considered were: overheating of the electric system with heavy smoke development, explosion of one of the high pressure bottles, failure of a cockpit window failure of the automatic pilot. However, no hypothesis could be formulated in which all occurrences and evidence could be made reasonably acceptable. Therefore, in November 1955, after a 15-months’ period of intensive investigation, the conclusion had to be drawn that the cause of the accident could not be established.”