From "AVweb":


"Risks" identified by a DOT's Office of Inspector General (IG) report
earlier this month "will impact the cost, schedule, and expected
benefits of ADS-B" and may feed off of each other until addressed by
the FAA.

The Inspector General said the greatest risks to successful
implementation "are airspace users' reluctance to purchase and install
new avionics" and "FAA's ability to define requirements" for the
advanced capabilities of that equipment.

The FAA has estimated overall costs on the user end could range from
$2.5 billion to $6.2 billion overall. And the FAA currently plans to
mandate only ADS-B Out by 2020. However, ADS-B Out "essentially
replicates existing domestic radar coverage," meaning adopters would
bear a cost but see few new benefits.

The main benefits of ADS-B rely on in-cockpit ADS-B In. But the IG
estimates FAA requirements and equipment costs for that feature "may
not be mature for at least two years." According to the IG, so long as
that mix of uncertainties remain, "progress with ADS-B will be
limited" and delays, cost increases and performance shortfalls "will
continue." There are other complications and the FAA has responded.

Aside from the cockpit side of ADS-B, the IG says integrating ADS-B on
controllers' displays also presents a significant and yet unmet
challenge. And on the foundation level, the IG says the FAA has failed
to update its cost-benefit analysis structure to ensure the most cost-
effective approach to implementation. The FAA has also not yet
assessed "staffing gaps or actions needed" to provide oversight once
the ground system is in place and being used to manage air traffic,
according to the IG. The report notes that the FAA is making progress
refining how ADS-B is put to work with airspace users, and makes
recommendations "to help FAA reduce risk" with the program's oversight
and implementation. The FAA agreed in full with seven of the nine
recommendations and has put forth plans to addressed them and meet
with the IG's approval.