Recorder Locations
1. The recorders are placed where they are least likely to be damaged in the typical crash. Of all the crashes in the jet age, only a handful have been into deep water.
2. The recorders may be used only once or twice in the lifetime of the airframe, if at all. The rest of the time they are dead weight. They may be used for FOQA, etc., but that is not primary purpose.
3. The recorders are certified with the airframe. Subsequent moving to another location would cost heaps of money, with little probability of return.
4. The recorders should be in a benign environment. That precludes mounting with the engine. The A330 FDR outside the pressure vessel is hardly benign, either.
5. The power to the recorders must be as secure as possible.