What is the lower altitude limit for the Foxtrot working Low Block?

The lower altitude limit for the Foxtrot working Low Block is indeed 4,000' MSL. This altitude is specified to ensure safe and effective air traffic management within the designated airspace. The term "MSL" refers to Mean Sea Level, which provides a consistent reference point for altitude across different geographical areas.

Airspace blocks, like the Foxtrot working Low Block, are clearly defined for various operations, including special use airspace, military training routes, and other controlled airspace where specific altitude restrictions are enforced to maintain separation between different types of air traffic. Operating above this limit helps to reduce the risk of collision and ensures that flight operations remain within established safety parameters.

While other altitude limits such as 3,000' MSL or 5,000' MSL may apply to different airspaces or operational contexts, the specific designation of 4,000' MSL for the Foxtrot working Low Block is crucial for maintaining the intended safety and efficiency of operations within controlled airspace.