Definition
An unintended flight condition in which the airplane's pitch attitude is more than 10 degrees below the horizon, and/or the airspeed is increasing rapidly toward or beyond limit speeds, often combined with an unusual bank angle. It is one of two recognized categories of airplane upset, the other being nose-high.
Plain English
The airplane has ended up pointing well below the horizon and is picking up speed fast — a situation the pilot did not intend and must recover from before the airspeed or load on the airplane gets out of hand.
Context Anchor
Seen in spiral dive and upset-recovery training when the airplane is descending with the nose down and speed building.
Derivation
“Nose” refers to the front of the airplane. “Low” means below the desired reference, usually the horizon. “Upset” comes from the idea of something being disturbed or thrown out of its normal state. Together, the term means the airplane has been disturbed into a nose-down condition.
Why Pilots Care
If not recognized and recovered from promptly, a nose-low upset can quickly turn into a high-speed spiral dive that risks exceeding the airplane's structural limits.
Grounding Statement
Picture looking over the cowling and seeing more ground than sky while the speed is increasing.
Intuition Check
“Upset” does not mean the pilot is emotionally upset. Here it means the airplane is not in the normal or intended flying condition. “Nose-low” does not always mean a small normal descent; it means the nose is lower than it should be for the situation.
Example Sentence 1
The instructor demonstrated a nose-low upset by rolling into a steep bank and letting the nose drop, then talked the student through the recovery.
Example Sentence 2
A nose-low upset during instrument flight can develop into a spiral dive if the pilot fails to apply the proper nose-up and wing-leveling inputs.