Of course, as with anything in life human error can come into play. Even a DNA lab may mistakenly switch samples or key in data incorrectly. All of these factors are possible, but also are very rare in occurrence. If there is ever any doubt as to the authenticity or correctness of a test it can simply be performed again to confirm accuracy.
Overall, DNA tests are the most accurate tests we have for using in situations where we need to know the positive identity of someone. They are the tests that do not lie, and cannot be influenced by taking drugs or other substances. Source: http://www.dna-paternity-test.net/how-accurate-is-dna-testing.htm
Requirements for doing forensic DNA testing are quite
high and unlikely to be available on a helicopter or a ship at sea.
Source:
http://www.fbi.gov/about-us/lab/codis/stds_testlabs
If you have the laboratory, known good
source taken from the person in the past, and tissue from the dead
person, you can then do an analysis. The key to the analysis is
something known as the PCR (polymerase chain reaction). PCR is
a method to analyze a short sequence of
DNA (or
RNA) even in samples containing only minute quantities of DNA or
RNA. PCR is used to reproduce (amplify) selected sections of DNA or RNA.
Previously, amplification of DNA involved
cloning the segments of interest into vectors for expression in
bacteria, and took weeks.
It is true that new procedures run by certified people
in land-based accredited labs, by certified personnel can now be done in
hours, but not likely in a helicopter or ship at sea.
Source:
http://www.medicinenet.com/pcr_polymerase_chain_reaction/article.htm