Airbus Helicopters H135 crash near Rotterdam, Netherlands

An ANWB air ambulance Airbus H135 (PH-TTR, manufactured 2017) and a Cessna F172N (PH-RES) came within 150 metres horizontal and 200 feet vertical separation east of Rotterdam The Hague Airport CTR. The helicopter was returning from a cancelled callout and had been cleared to enter the CTR at 1,500 feet or below. The crew descended to 800 feet while troubleshooting intercom noise. The Cessna, on an instruction flight using the VFR Mike Departure at 1,000 feet, was not visible on the helicopter's traffic advisory system because the aircraft transponder was set incorrectly. Both aircraft made evasive manoeuvres to the right. The Dutch Safety Board found the controller had issued clearances that placed both aircraft on opposing tracks. High traffic volume (two IFR and eight VFR flights) and a defective fuelling station generating extra radio traffic contributed to the controller's failure to issue conflict traffic information.