During the landing, the pilot lowered the helicopter air ambulance down to the concrete pad. Shortly before touchdown, a cloth fire extinguisher cover from a nearby mobile fueling unit was blown airborne from the main rotor system wash. The cloth fire extinguisher cover was ingested into the tail rotor (the fenestron). During the cloth fire extinguisher cover ingestion sequence, the fenestron hub flexed, the metal fenestron hub cover detached, and it was also ingested. The pilot was able to land the helicopter without further incident. The helicopter sustained substantial damage to the fenestron. The evidence indicated that the ingestion of the metal fenestron hub cover contributed to the severity of the damage sustained. The operator reported there were no preimpact mechanical malfunctions or failures with the airframe and the engines that would have precluded normal operation. The investigation revealed that the cloth fire extinguisher cover, which did not have a lanyard installed, was not secured with the retention bracket for the fire extinguisher on the mobile fueling unit. The operator additionally reported that foreign object debris checks are conducted by crew members anytime they are on the pad and that the mobile fueling unit is inspected during the daily fuel quality check. The Accident Investigation Board Norway along with the European Aviation Safety Agency, previously issued a formal safety recommendation to Eurocopter (Airbus) regarding the securement of the metal fenestron hub cover.