Possible Clues:

• Sounds like flyer moving through water process is uncomplicated
• Smooth easy progress
• Easy progress
• Unobstructed progress
• Easy progress of prairie schooner?
• Student in agonies, suffering - but it's easy!
• Frank's in poor health, but making smooth progress
• Steppes under the weather provide easy progress
• Schemes in a bad way to restrict current smooth progress
• No problem (for yachtsman?)