Old King Coal
re fake or otherwise, if referring to #253 the video audio is consistent with the NTSC accident report readout, and if you run an FFT of the audio and check SPL, the later part is consistent with the rapid descent and the break up of the aircraft, you can do the maths on the acoustics from the cruise state to determine the increase in air noise, which is an analogue of freestream flow levels (gotta account for the normal shock-related noise over the top of the cockpit). Take an example of the time deltas between any of the transmissions noted in the report and the audio, and they are accurate to 1 millisecond, so I would discount the proposition that the audio is faked.
The original report (KNKT/07.01/08.01.36 BOEING 737–4Q8 PK–KKW MAKASSAR STRAIT, SULAWESI REPUBLIC OF INDONESIA 1 JANUARY 2007) did not include a complete transcript of the CVR, but did include partial transcripts of the A/G Comms and of the cockpit comms leading up to the upset, including the discussion on the IRSs and the GPWS Mode VI Bank Angle callouts. The FDR transcript of the last 2 minutes of the flight is in the report.
- The audio is consistent with the SPL of the spectrum.
- the timing between comms from Ujung to the aircraft is consistent with those that occurred.
- the time between the comms and the breakup event indicated by the rapid reversal of g load from +3.5 to -2.5 is consistent with the data in the report.
The audiotape of Adam Air 574 should never have been released to the public domain, there is no legal or social value from it, however, the audio is highly probable to be genuine. There is nothing in the audio that contradicts the analysis, conclusions or recommendations that NTSC (KNKT) made in their report.
As an aside I had input to the investigation as an independent expert related to the flight path, and was aware of the data, but had never previously heard the audiotape until this link was shown. (Previously I had used CVR SPL to determine the engine state and the CAS of a widebody accident where the DFDR was destroyed totally.)
The calculated highest speed encountered was transonic, just below sonic, recovery was severely compromised before the structural failure of the tail finally removed all question.
[Years after this in dive test of this wing we ran a 3D DES analysis of the wing at high speed and showed that eventually, the aircraft would encounter a collapse in CL from the wing for a given AOA, expected, which was caused by the formation of a lower surface normal shockwave, not so expected... which then led to an analysis as to the trim change that would arise, for a given stab setting. In the end, it looked like the flight path would tend to lower rapidly due to loss of lift, while the trim would tend to offset that slightly, the net result being a pitch down. The loss of lift was coincident with the development of normal shocks on the bottom of the wing. In the end, running out towards MDive we descended with power on so that a thrust reduction would permit a reduction in speed, and we were quite happy not to go too far outside of the MMO of the aircraft to demonstrate compliance with the Part. Axelson in 1947 wrote a good memorandum (NACA RM A7024) which spoke about the effect on longitudinal stability from the collapse of main wing lift AOA slope at higher Mach. the conventional wisdom of Mach-tuck causation (AP3456A, aero for "non-marines" etc) being from the effect of the aft movement of Cp with shock migration rearward with increasing Mach, and the change in downwash incidence to the tail appeared to be only a partial truth, the development of a shock on the lower surface of the wing altered the zero-lift AOA considerably, and that meant a collapse if CL, which has an adverse flight path angle effect]. So, what the heck, why rabbit on about the cause of the pitch down... simple; the cause is from a reduction in the zero-lift angle of attack, so to get the same lift as before, the wing has to be at a higher AOA than the trim point, therefore all else being equal, the flight path will decay, unless. more nose-up trim is applied, which we see as an effective pitch down moment. The moment is actually not significantly altered, it is that case that the flight path degrades for the given trim state; it May sound like semantics, but if you are out in that region, it gives a hint on avoidance and recovery. Notably, the collapse of CL that occurs is coincident with a reduction of the Cm, and that was the reason for going into the analysis in some depth, as conventional wisdom suggests that wing Cm increases from the migration aft of the Cp, and, it does not.
The Adam 574 tape is adequate to determine the frequency of the cooling fans are in the background, which indicates what the engines were doing in acceleration or deceleration, which happens to be consistent with the DFDR data anyway, not a surprise, but supporting the authenticity of the recording. About the only curiosity coming out of the CFR tape vs the report is that the thump sound that was considered to be the commencement of the breakup of the tail, while it is at the same time as the vertical g reversal, is about 4 seconds before the highest pitch attitude in the recovery, at which point the nose drops once again. The later pitch rate reversal is the greatest rate that is recorded, and probably results from a final farewell of the horizontal stab, following the loss of elevators 4 seconds earlier... at that later moment, there is a very large lateral acceleration, possibly the horiz stab going off in pieces.
For what it is worth, the plane held together longer than any design requirement would require. The aircraft was completely recoverable had the wings been rolled to level earlier while the guys were pulling high g. The bank angle was over 30 degrees for more than a minute, and beyond 90 degrees for over 16 seconds, while pulling g between 1.5 and 3g Had the bank been reduced to near level at any reasonable time, the recovery was possible, but history shows we still have more hard learning to do then on recovery from UA, as occurred with AF447 etc.
FFT of ADAM AIR 574 questioned CVR recording