fotoguzzi; Often, a company such as Boeing will have some key engineering personnel known as DERs (Designated Engineering Representatives) who approve or recommend for approval designs to the FAA. (see:
Designees & Delegations - Designated Engineering Representative (DER)).
There is some controversy regarding the over reliance that the FAA has on the work product of these DERs. Boeing clearly didn't 'sneak' a LiON battery onto the 787. They requested an exemption to current rules restricting the use of this battery technology onboard aircraft. So now the questions are: Did Boeing (or more accurately Boeing's subcontractor) consider all of the environmental factors and conditions of use placed on the battery when doing its testing and analysis? And did the FAA miss anythging when reviewing the DER's work product?
Often times, Boeing, or some systems subcontractor will define the conditions under which a component will operate and request that the component be designed and tested to those conditions. But due to a lack of understanding of systems integration considerations, those conditions may be poorly defined. The component will pass tests under the specified conditions. But some aspects of its use may push it beyond its design limitations.
Given that there are several layers between the component suppliers, systems contractors and Boeing, the finger pointing may soon commence.