The FTCA (and most state tort claims acts) preserve immunity from tort liability
for the discretionary acts of government employees. This discretionary function
exception is perhaps the most notable and complex exception to FTCA liability.
A discretionary function is an act involving an exercise of personal judgment.
The basis for the discretionary function exception to the FTCA is the legislative
branch's desire to prevent judicial second-guessing through tort actions of
legislative and administrative decisions grounded in social, economic, and
political policy. The federal government retains immunity from tort liability for
itself and its employees for the performance or nonperformance of
discretionary functions. This immunity is granted when the act in question
requires the exercise of judgment in carrying out official duties. Discretionary
immunity applies unless a plaintiff can show that a reasonable person in the
official's position would have known that the action was illegal or beyond the
scope of that official's legal authority.
Harlow v. Fitzgerald, 457 U.S. 800
(1982). U.S. v. Varig Airlines, 467 U.S. 797 (1984)
is a major case concerning the
discretionary function. Here, the federal government was not held liable in a
negligence action. A plane caught fire in midair and although it landed safely,
many on board died from asphyxiation. The airline and survivors brought suit
against the federal government for negligently certifying that the airplane met
the applicable federal safety standards based upon a spot-check which did not
include every aspect of safety. The Supreme Court held that the inspection was
discretionary, and the government was therefore not liable. The Court did not
want to involve itself with policy and the distribution of limited resources,
which is how it viewed the safety inspection policy of only checking certain
aspects of the plane for safety. 
