Direct answer: No. Air marshals are not on every flight. They operate selectively, with a small fraction of flights having an air marshal onboard, and the presence is determined by internal risk assessments and security needs.

Context and details:

• The Federal Air Marshal Service (FAMS) cannot cover all daily US commercial flights, given the sheer volume of flights versus available marshals. Estimates often place marshal presence on a minority of flights, with higher likelihood on longer or high-risk international routes.

• Independent assessments and reporting commonly cite figures in the single-digit percentage range for domestic flights having an air marshal aboard, and even lower for certain routes, though high-risk destinations may see higher probabilities.

• Some sources note that other countries or airlines employ their own security measures, and unique operators (e.g., El Al) have different policies, but in the United States the standard practice is selective deployment rather than universal coverage.

If you’d like, I can pull up the latest official statements or GAO reports to provide precise current figures and the methodology behind the risk-based selection.