This clip explain the notion of flight envelop. The higher is flying the plane the smaller is its speed limits (called flight envelop). Depending of wheather conditions and altitude it could be as small as 30 knots. In degraded situations when the pilots are loosing their automatic pilot and their speed indications, it could be challenging to maintain the airplane in it's flight envelop specifically when the weather is turbulent (wind speed can reach 50 knots).

Cette vidéo décrit brièvement la notion d'enveloppe de vol. Tous les paramètres susceptibles de modifier cette enveloppe ne sont pas décrits (température, facteur de charge, position des gouvernes de vol, centrage, etc.). En vol de croisière, les avions cherchent l'altitude maximale pour minimiser leur consommation de carburant.

This video clip explains the notion of flight envelope. Mastering this notion is mandatory to understand big jets difficulties when they flight in turbulent weather.

Simulateur : X-Plane