What safety issues led the FAA to ban Constellation flights into/out of the U.S.? Although the Lockheed Constellation (like the other late, large piston airliners) was superseded in the 1960s and 1970s by newer jets (plus turboprops for shorter/lighter routes), it hung on into the 1990s with various Latin American airlines, who used them for international flights to and from the U.S.; this only ended in 1993, when the FAA abruptly banned the last of these airlines (all of them from the Dominican Republic, weirdly enough) from flying their Constellations in U.S. airspace.  According to Wikipedia, this ban was due to some sort of safety concerns:


  Most Super Constellations were retired by their original operators after the advent of the Boeing 707 and Douglas DC-8 jet airliners. The last commercial flight of the L-1049 Super Constellation was in 1993, when the Federal Aviation Administration banned all airlines from the Dominican Republic that flew Constellations to the United States (due to safety concerns). The Dominican airlines were the last operators of any version of the Constellation.


I’m at a loss as to what those safety issues could be:


Was it due to concern about poor safety practices at those airlines, rather than concern about poor safety of the Constellation per se (but, then, why weren’t there at least one or two Constellation-flying carriers that did meet the FAA’s safety standards)?
The Constellation being an old, pressurised aircraft, were they worried about metal fatigue (but, then, why did the FAA impose a total flight ban on the Constellation, when fatigue-life concerns haven’t caused them to impose such a penalty on any other aircraft - especially since fatigue would be less of a concern with piston airliners like the Constellation than with jetliners, due to their lower cruising altitudes and resultant lower cabin pressure differentials)?
Were the old, large, temperamental multi-bank radials used by large piston airliners such as the Constellation simply incapable of meeting increasingly-strict engine-reliability requirements?
Was the FAA casting a jaundiced eye on the safety hazards of U.S. airports having to store vast quantities of the extremely-high-lead grades of avgas needed by the aforementioned engines?
Something else?
Individual airlines, or even all of the airlines from entire countries, are sometimes banned for safety reasons. It was the Dominican airlines, not the aircraft, that were banned by the FAA.

It is just coincidence that many of these un-safe airlines flew Lockheed Constellations. They were banned from flying ANY aircraft into the USA. 

The Wikipedia article talks about the end of Constellations used in commercial airline service, but it was the grounding of the airlines that caused the end, not the grounding of any particular aircraft. 

Here is a link to a NY Times article describing a ban of all airlines from nine different countries. 

Sept 3rd 1994 NY Times article


  The Federal Aviation Administration has barred airlines from nine nations from flying to the United States because of poor safety procedures.
  
  The unusual action, announced today, is a response to safety questions
  from consumer groups. Officials say they hope the economic fallout of
  the ban will encourage the airlines to follow safety guidelines.
  
  The aviation agency surveyed safety procedures in 30 of the 93
  countries that have commercial flights to the United States. The
  agency sought to determine if the aviation authorities in each country
  were meeting the safety requirements of the International Civil
  Aviation Organization, a United Nations agency. Its rules are less
  strict than those of the Federal Aviation Administration.
  
  The aviation agency did not reveal details about the safety
  deficiencies that had prompted it to ban the nine airlines.
  
  The banned airlines are from Belize, the Dominican Republic, Gambia,
  Ghana, Honduras, Nicaragua, Paraguay, Uruguay and Zaire. Four other
  countries were allowed to continue flying into the United States, but
  under increased supervison by the aviation agency. They are Bolivia,
  El Salvador, Guatemala and the Netherlands Antilles.