To follow up on Chris Scott's query and ionagh's reply, here are a few links from twenty years ago to problems the US Army may have had with EMI affecting its Black Hawk helicopters (I emphasise the words "may have had", in contrast to "did have"!). The Navy apparently did not have similar concerns with its Sea Hawks: they were better shielded because of the extremely EM-loud shipboard environment.
All from the Risks Digest:
From Risks 5.56
From Risks 5.58
Also from Risks 5.58
From Risks 5.59
From Risks 5.60 and a cautionary note from me:
in Risks 5.59
PBL