Dave
You may have heard of the phrase "past performance is not an indicator of future performance"? Just because the Viggis/Vikings hadn't crashed in recent memory then it didn't mean they were safe - remember the Nimrod? Never had a mid air explosion before its fatal one in 2006 and it had been flying since 1969. Before 2 Sep 06 the Nimrod loss rate due to mid air fuel fires was also zero - it then had the fatal one in Sep 06 and also had another serious leak in mid air in Nov 07, shortly after AAR was suspended for good on the MR2 and the type was retired just over 2 years later.
Aircraft can lose their airworthiness real quick!
LJ