Possible Clues:

• Thing that can bring you down?
• It keeps you grounded
• Downward pull somewhat strong, for certain
• It's zero in free-fall—and, put another way, a hint to how the four longest puzzle answers were formed
• Measure of acceleration due to gravity
• NASA measurement
• Jet pilot's concern
• It puts pressure on pilots
• Aerospace measure
• Power of pulling, for certain?