Proposed changes to Parts 25 and 33 address dangerous icing conditions caused by supercooled large drops including a requirement that manufacturers not only show that airplanes can operate safely in those conditions but also with specific performance and handling qualities and that “all new transport-category designs be able to fly in conditions where supercooled liquid and ice crystals exist.” Changes would add new icing certification standards for engines and engine installations and components such as angle of attack and airspeed indicating systems. Interestingly, this rulemaking would finally close a significant gap between Part 23 and 25 icing certification standards. There is a stricter requirement for Part 23 airplanes: that they be “capable of operating safely in continuous maximum and intermittent maximum icing conditions,” and to specific “performance, controllability, maneuverability and stability” standards. Part 25 airplanes “must be able to operate safely” in the same conditions, but there is currently no definition of what “to operate safely” means. Comments are due by August 30.