Definition
An approach to landing in which the airplane is not established on the proper flightpath, airspeed, configuration, descent rate, or power setting required for a safe landing, and in particular one flown at an airspeed below the recommended approach speed where the airplane is operating on the back side of the power curve. In this regime, increasing pitch to arrest sink rate increases drag faster than available thrust can overcome, producing irreversible deceleration and an increasing sink rate that cannot be corrected before ground contact.
Plain English
A landing approach that is too slow or otherwise out of control — wrong speed, wrong descent rate, wrong power, or wrong path — to the point where the pilot can no longer fix it before touchdown. Pulling back on the yoke to slow the descent only makes things worse because the airplane is already too slow.
Context Anchor
Seen in landing training, stabilized approach discussions, and go-around decision-making near the runway.
Derivation
“Unstable” comes from “stable,” meaning firm or steady, with “un-” meaning not. “Approach” means coming near something. Together, the phrase points to an airplane that is nearing the runway but is not steady, properly placed, and ready to land.
Why Pilots Care
These approaches are a leading factor in landing accidents; spotting them early lets the pilot go around before the situation becomes unrecoverable.
Grounding Statement
If the airplane is low, slow, and still not properly lined up close to the runway, there may not be enough time or energy left to fix it before touchdown.
Intuition Check
“Unstable” does not mean the airplane is shaking. Here it means the approach is not within safe, planned limits for path, speed, descent, and landing readiness. “Slow” does not mean calmly or carefully; it means the airplane may not have enough airspeed for a safe landing correction.
Example Sentence 1
The instructor called for a go-around when the student's unstable, slow approach left the airplane high, off centerline, and well below the recommended final approach speed.
Example Sentence 2
Maintaining the correct airspeed on base leg helps prevent unstable or slow approaches to landing in gusty wind conditions.