Thread: AF447
View Single Post
Old 27th Sep 2009, 01:53
  #4476 (permalink)  
mm43
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 76
Posts: 1,331
Where were they?

I'm throwing a new graphic into the mix, but before going any further lets have a look at the AOC reported positions. On departure Rio de Janerio the 10 minute AOC reports were noted at 09, 19 etc.., but prior to passing NATAL it is assumed that AF Operations reset the report timing to 10.5, 20.5 etc., probably so that they would get regular sequencing of reports from multiple aircraft, rather than a disorganised dump every 10 minutes. To complicate the issue the BEA produced a route chart showing the report times as clearly occurring on the minute. Based on the timings produced by the BEA, many moons ago I deduced that AF447 was overhead INTOL at 01:32:32 whereas it can now be assumed the time was 01:33:02. This is important because there is currently no rational for the apparent deviation from the track originally noted at 02:10:00 to have occurred prior to the upset that happened at 02:10:06 when the ACARS commenced phoning home.

02:10:10 - AUTO FLT AP OFF
02:10:16 - AUTO FLT REAC W/S DET FAULT
02:10:23 - CTL ALTN LAW
02:10:29 - FLAG ON CAPT PFD SPD LIMIT
02:10:34 - 02:10:30z AOC Position Report [injected into ACARS sequence as priority]
02:10:41 - FLAG ON F/O PFD SPD LIMIT
02:10:47 - AUTO FLT A/THR OFF
02:10:54 - NAV TCAS FAULT
02:11:00 - FLAG ON CAPT PFD FD

Other than the AOC position, it can be assumed that remaining items all originated at 02:10:06 (4 secs to receipt at AF Maintenance Base). Note the AUTO FLT AP OFF, AUTO FLT A/THR OFF and NAV TCAS FAULT are possibly due to discrepancies in Pitot ADM and Baro ADM static pressure data [Note:: The rejection by the EFCS of an invalid IAS due to more than 30KTS reduction in 1 second, doesn't happen until just over a minute later]. On the otherhand, the initial ACARS fault messages could have been caused by control parameters being exceeded, e.g. extreme turbulence, updrafts / thermal elevator, or extreme wind shear involving Loss of Control in what would be a Coffin Corner situation. A Mach Critical event seems to have been avoided.



A larger scale graphic is available at -
http://i846.photobucket.com/albums/a...7-bank-lge.png

A turn radius for a 20 degree bank (grey circle), and the 02:10:30z AOC position would have resulted in a deviation from the track initiated at 02:09:30z. Indications are that the GS from the 02:00:30z position to the 02:10:30z AOC position had remained constant at 463KTS (475KTAS). However, what was happening to the OAT?

Consider each of the following scenarios -
(1) That the Cb cell updrafts in the ITCZ were conveying an unusual amount of water vapour/latent heat which was carried out into the anvil stratus cloud radiating from each cell. The a/c encountered this cloud around 0208z and the incremental ice-up of the pitot tubes, some other surfaces and potentially the engine cores took place over the next two/three of minutes. Likewise the ATHR augmented decreasing IAS/CAS with increasing power. Whether the left turn that is already evident in the 02:10:30z AOC position was crew initiated or took place as a result of a LOC event is unknown - my supposition is that its related to the 02:10:06z events.

A turn radius for a 35 degree bank (white circle), and the 02:10:30z AOC position would have resulted in a deviation from the track initiated at 02:10:00z.

(2) Take onboard the first paragraph in (1), then assume that the a/c effectively penetrated the active Cb cell, hit the wall and rode the thermal elevator, then the 02:10:30z AOC position represents where it had been thrown as it was spewed out of the mesoscale system. The BEA know a lot more about the 0210z position than they have let on - enough said.

Throw in a double flame-out, the AP/ATHR disconnect, ADIRU's disagreeing, unbelievable IAS along with sundry chirps and bells, then it doesn't take you long to realise the only way is down and how the hell do you manage it. On top of all that the FBW software, when it gave up, gave you back the a/c with control limitations!

A turn radius for a 45 degree bank (cyan circle), and the 02:10:30z AOC position would have resulted in a deviation from the track initiated at 02:10:06z, i.e. AP/ATHR OFF.

The debris distribution and current data indicate that the a/c continued in a westerly direction and descended in probably heavy turbulence to possibly FL100 over the next 3min 10sec - averaging nearly 8,000 feet/min with a KTAS of about 408 (+/- wind) and GS of 400KTS. If a high altitude 2 x flame-out had occurred, then sufficient turbine rpm was being maintained to power the essential service bus during this descent. Attempts to relight may have been hampered by turbulence and ice load. Reducing the rate of descent near FL100 then resulted in electrical power loss at 02:13:10z and it is presumed the APU was started as evidenced by resumption of the SATCOM link at 02:13:40z.

Remember, the a/c was deep in the ITCZ descending through numerous cumulonimbus cells and associated out-flowing anvil cloud with the propensity for ongoing icing highly likely.



Putting together a new graphic to represent more clearly what may have occurred, I looked at the 3 separate positions I had previously calculated for the possible impact position and decided they represented the proverbial "cocked hat". Bisecting the internal angles through the center of each opposite side gave me a position of 303.4'N 3104.5'W, and this position when plotted gave the track (magenta line) from the Last Known Position as plotted tangential to the 35 degree bank curve.

As previously suggested, the Cabin Vertical Speed advisory gives an indication of when the a/c was passing through about 8,000 feet - 5 secs after the external pressure exceeded the cabin pressure and cabin vertical speed exceeded 1,800 ft/min.

In summary:-
(1) WX radar faulty or crew didn't detect Cb cell(s). Probably former.
(2) LOC at FL350+/- was as a result of extreme conditions encountered when penetrating an active mesoscale system.
(3) Icing that took place was probably 'rapid' as opposed to 'gradual'.
(4) Intake blanking in the updrafts resulted in a 2 x flame-out.
(5) Recovery was achieved, but relights were unsuccessful due to engine core ice load.
(6) The low level LOC could have been compounded by an aft C of G problem.
(7) Tail yawing to port? A 'flat spin' or just surface wind 025T x 21/35KTS.

Finally, I'm just the messenger!

mm43

Last edited by mm43; 27th Sep 2009 at 21:15. Reason: spelling!
mm43 is offline