A Lufthansa Regional Avro RJ85, D-AVRN (msn E2293), suffered a serious icing incident on 21 March. She was operating flight LH4062 from Frankfurt to Firenze. While climbing through 11,000 feet, significant pitch oscillations began that the crew had difficulty controlling. Controllability increased substantially once the aircraft had descended below 8,000 feet. The RJ85 landed safely at Stuttgart a short time later. None of the 86 passengers and crew on board were injured. An investigation is underway, but it is suspected that deicing fluid residue built up and froze. Type II and IV deicing fluids, which have thickening agents to enhance hold times, have proven to be particularly susceptible to such problems.