Incident Description
The flight was vectored for an ILS runway 3R approach. ATIS information indicated moderate mixed icing in clouds. The captain reported that the aircraft entered cloud tops at 5500 feet, remained in clouds for approximately 5 minutes, and accumulated about 1.5 inches of rime ice. The ice accumulation was rapid, so the crew decided to wait until they were in clear air to cycle the de-ice boots, to prevent bridging.
After intercepting the ILS glide slope on a coupled approach, the aircraft was slowed to extend the landing gear and flaps. A call for "flaps 15" was made, and approximately 3 seconds later, the autopilot disconnected as the aircraft was descending through about 1900 feet AGL at approximately 146 knots. At approximately the same time, the de-ice boots were cycled as the aircraft broke out of weather, and the aircraft went out of control. It entered bank oscillations (up to 44 degrees) and abruptly lost about 500 feet before the crew recovered. The aircraft landed successfully.
Investigation Findings
Investigation revealed that the recently trained crew did not receive sufficient training in the use of de-ice equipment from company instructors, who had themselves been trained at the factory.
Aftermath
After this incident, the manufacturer revised the flight manual to provide more specific information regarding de-ice operations.