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stabilator
20th Nov 2016, 02:35
Hello all,

I have a somewhat out of the ordinary question, put simply, how sensitive are recorders to damage in the tail area? There have been several cases where damage has occurred in the tail area which has stopped recorders from recording, even though the damage wouldn't seem to have affected the reorders

here are the examples:

AA 587 (A300), FDR stops recording seconds (2-3 sec) after vertical stabiliser separates. Why would such damage affect the FDR?

DHL 611 (757), FDR and CVR stop recording shortly (8-9sec) after a large portion of the vertical stabiliser is torn off. Same as above, how would that affect the recorders?

EK 407 (A340), FDR stops recording following a tail strike on takeoff after sliding out of its mount. Strange and unusual that a tail strike can dislodge a recorder.

It seems that under some circumstances the recorders can be quite sensitive to stopping when damage occurs near them, I'm also wondering why the recorders can seemingly randomly stop recording several seconds after the damage has occurred? For example The DHL report states that the CVR recorded for 9 sec and the FDR recorded for a further 8 sec following the damage (with the last 7 sec of the FDR tape being damaged).

Regards,

Stabilator

vapilot2004
20th Nov 2016, 12:18
Signal/data and power wiring typically runs along the crown of the aircraft and most DFDR and CVRs are installed above the ceiling (beyond the fascia) near the root of the vertical stabilizer. Damage to this area could interrupt power or input channels, both of which would stop the data recording process.

Sevarg
20th Nov 2016, 20:19
The 340 sounds like the cvfdr or whatever wasn't fitted correctly, ie the retaining nuts failed to engaged. The other two I would guess at the G switch tripped. Can't remember what value they trip at but on helicopters a good slap would switch off the cvfdr. I would guess it would be less for fix wing.

stabilator
21st Nov 2016, 11:52
Thank you for the responses, I didn't realise the recorders were so close to the Vertical stabiliser, I suppose anything related to that damage could affect them in that case, leaking hydraulic fluid for example? Also I also dont know what will trip the G switch, its probably fairly high, but without a V-stab the aircraft were subject to large lateral G's, I suppose this also may have tripped them perhaps, I dont imagine the lateral G threshold is that high