A post from nearly a year back that seems worth repeating
The COTS dogma is an abject failure, when attempting to use a civilian-designed and certified helicopter.
In each and every case, requirement creep catches up to the machine. This causes schedule delays, performance hits, and budget overruns.
S92 - CH148 : 4 years late now, millions over budget, and still no completed IDMGB or mission system package
VH71 - AW101 : Billions over budget thanks to insane requirement changes midway though the design process
CSARX, VXX : All axed due to inflated costs in the face of progressively tighter budgets
EC145 - UH72 : One of the few touted "success stories", but this is because this machine was not very militarized and its mission is designed almost exactly the same as its civil counterpart (quite a rarity). That said, even this helicopter had some fairly major issues with its new avionics overheating, which required the addition of some fairly ungainly cooling equipment cutting into its capacity.
The idea that taking a COTS machine and "cheaply" obtaining your military helicopter is deeply flawed and this has been proven over recent history. The customer always realizes (after the contract award) just how much of a compromise it is to be constrained to the COTS product performance, and then tries to redesign it to such an extent that the process breaks down.