# Buffet Onset & Flight Envelope

> V-n diagrams and the aerodynamic ceiling.

- **Subject:** 081 — Principles of Flight
- **Section:** 081-03 — Stall, Mach Tuck and Upset Prevention and Recovery
- **Topic code:** 081-03-02
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/principles-of-flight/stall-mach-tuck-and-upset-prevention-and-recovery/buffet-onset-boundary/

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## Buffet Onset Boundary
The boundary in the flight envelope where buffet occurs.
*   **Low Speed Buffet**: Caused by airflow separation at high angles of attack (approaching stall).
*   **High Speed Buffet**: Caused by shock waves forming on the wing (approaching Mach limit).

## Aerodynamic Ceiling (Coffin Corner)
As altitude increases:
1.  **Low Speed Stall Speed (IAS)** increases (due to compressibility effects).
2.  **High Speed Buffet Speed (Mach)** decreases (Local Speed of Sound decreases).
*   At a certain altitude, these two speeds converge.
*   The pilot has a very narrow margin between stalling (too slow) and overspeeding (too fast).
*   This point is the **Aerodynamic Ceiling**.

## Load Factor ($n$)
Increasing Load Factor (e.g., in a turn or turbulence) increases the Stall Speed.
$$ V_{stall_{new}} = V_{stall_{1g}} \times \sqrt{n} $$
*   Therefore, the margin to buffet decreases when maneuvering.
*   **1.3g Buffet Boundary**: Altitude where the aircraft can pull 1.3g (40° bank turn) before encountering buffet. This is typically the practical operating altitude limit.

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