What happened
On November 7, 1999, a Hughes 369 D helicopter, registered in the USA and based in the United Kingdom, departed from Marl-Loemühle for a private flight to Idar-Oberstein. The flight was conducted under Visual Flight Rules (VFR). At approximately 11:55 AM, the pilot, accompanied by one passenger, began an ascent. While the pilot initially managed to fly above the cloud layer at roughly 3,800 ft, the weather conditions deteriorated as the flight progressed.
At 1:22 PM, the radar controller informed the pilot that continuing the flight to the destination under VFR was not possible and inquired if the pilot could proceed under Instrument Flight Rules (IFR). The pilot declined IFR capability and requested a radar-assisted descent through the clouds (cloud breaking), which the controller denied due to the pilot's lack of IFR certification. The pilot then decided to return to Marl-Loemühle, turning onto a northern course without prior coordination with the controller.
By 12:30 PM, the pilot reported encountering icing and requested a descent to 3,500 ft, confirming the aircraft was still within the clouds. The helicopter continued to descend to 2,500 ft. At 12:34 PM, the pilot declared a Mayday emergency but did not provide specific details, again requesting a radar-assisted descent. Although the controller offered radar vectors to Cologne-Bonn Airport, the aircraft began to lose altitude rapidly, at an average rate of over 1,300 ft/min. The final radio transmission was recorded at 12:36 PM, with the pilot stating, "we are out of..." before contact was lost. At 12:37 PM, witnesses observed the helicopter emerging from the clouds with a severe nose-down attitude and impacting a field in Lindlar-Fenke. The impact resulted in two fatalities and the total destruction of the aircraft.
The investigation
The BFU investigation examined the crash site and analyzed radar data and radio communications from the Deutsche Flugsicherung (DFS). Physical examination of the wreckage showed no evidence of mechanical failure. The investigation established that the weather at the accident site was foggy and rainy, with visibility below 1 km and cloud ceilings as low as 200 ft. Radar analysis revealed that the pilot performed unauthorized turns and failed to maintain the requested altitude during the emergency. The investigation also noted that the pilot was flying a US-registered aircraft without the proper legal authorization required for such operations in Germany.