Here are 4 facts, and 4 questions arising from them:
Facts:
(1) There is a notation on the FDR report of a [sound similar to altitude alert] about 20 seconds before the FDR stops.
(2) This sound occurs right in the middle of the drop in the engine pressur ratio [EPR] of the #4 engine, which itself takes about 6 seconds.
(3) During and following this drop on #4, #1 and #3 show slowly rising EPRs over the about 18 seconds.
(4) The Chinese radar recorded returns for about 9 secs. after the last transponder signal recorded by the CAA.
Questions:
(a) What conditions could give rise to an [altitude alert] at 34,000 ft.?
(b) Is there any way that a small drop in an ERP could give rise to an [altitude alert], or an audible alert similar to an [altitude alert]?
(c) Are these EPR changes (#4 down, followed by #1 and #3 slowly increasing) a normal operation? e.g. for trimming purposes. Would this be an auto pilot action?
(d) The CAA recorded no transponder signals for a period of 30+ seconds about 4 mins. before the recorders on the a/c stopped. I am curious to know whether the Chinese radar recorded any transponder signals during this gap.