This dissertation grew from a review I did of positions presented in Tim Vasquez's weather analysis of conditions he expected would have been encountered by AF447 enroute from its last known position at INTOL on Airway UN873.
My original calculations, that alerted me to a potential error in the positions, were not correct either! I had transposed a ground speed. On top of that the only fact we had was the last report from AF447 at INTOL and the manner in which the TASIL position had been derived was from a questionable news report stating TASIL was expected within 50 minutes.
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The reported 0214z position - 3° 34' 40"N 30° 22' 28"W couldn't be verified and it was 8.5NM left of track. I then tracked down the Flight Plan and decided to apply Mach 0.82 and work on from there. The following was actually written for inclusion in the Discussion Page associated with the Wikipedia AF477 article:-
There is a great deal of misinformed speculation as to positions said to have been reported by AF447. The sources quoted are newspaper articles, themselves without identifiable sources. INTOL 1° 21' 39"S 32° 49' 53"W at 0133(UTC) and expecting TASIL 4° 00' 18"N 29° 59' 24"W within 50 minutes. The distance between these way-points is 364 nautical miles, and if an ETA of 0223(UTC) at TASIL is assumed, the aircraft will need a Ground Speed of 437 knots.
The Flight Plan filed showed Mach 0.82 at a flight level of 35,000 feet. Conversion at sea level of Mach 0.82 gives 543 knots, but when corrected for the forecast air temperature of -46C at FL350, a factor of 0.88 needs to be applied, resulting in a True Air Speed of 477 knots. Meteorological data derived for this period indicated a head wind factor of 10 knots which results in a ground speed of 467 knots.
Based on the information provided in the preceding paragraph, the aircraft's position report at INTOL would have been in the following format:-
"Air France 447, INTOL 0133, Flight Level 350, next TASIL 0220, Ground Speed 467, Temp -46".
NOTE: The TASIL 0220z matches the Brazilian Air Forces published time.
As mentioned by others, the 0214(UTC) position was not provided by ACARS and is someones "guesstimate" of where the aircraft was at that time. Also consider that Mach 0.80 is the aircraft type recommended turbulence penetration speed, and the aircraft would most likely have been slowed prior to 0200(UTC) - flight parameters permitting.
The Brazilian Air Force are basing their search on the following 0214(UTC) position:-
3° 16' 28"N 30° 22' 28"W, which is at variance with the -
3° 34' 40"N 30° 22' 28"W position attributed in the Wikipedia article, though strangely similar!
Identified debris has now been recovered from near 3° 34'N, 30° 28'W, or 343°T by 18NM from
3° 16' 28"N 30° 22' 28"W, and with the Atlantic Northern Equatorial Current in this position setting generally NW at between 3 - 6NM per day, though likely to tend more to the north at the onset of the North Equatorial Counter Current, debris will probably be found over a wide area.
I suspect the aircraft was essentially on time and on track and any advance on these positions was possibly due to an overspeed event, or tail winds resulting from the ITCZ weather event as detailed by Tim Vasquez .
Secondary Surveillance Radar (SSR) at Fernando de Norhra received the last "squawk" from AF447 at 0148z, and there have been media reports that the ground speed was 453 knots at that time. The only way the ground speed could be established would be by the CINDACTA III (Brazilian Oceanic ATC) using successive plots from the SSR. Should this report be true, then the Mach number required to get the aircraft to either of the last noted positions would have been excessive for the known conditions at the time.
It is worth noting that normal compliance with Oceanic ATC requirements would mean that the aircraft should have requested clearance to deviate left or right of track by, e.g. up to 20 or 50 miles. Such clearance when given, would have required the aircraft to report when back on track. This procedure would be strictly followed in this area where there are many parallel airways. No such request appears to have been made, at least not via HF.
The widely reported ACARS 0214z position - 3° 34' 40"N 30° 22' 28"W could not be verified, but it is not normally transmitted by the ACARS system, though a "so called" GPS position may have been incorporated in the data stream sent at that time presumably via the Satellite Communications link. The position sent is derived from the aircraft's integrated flight navigation system (FANS-A), so essentially relies on the integrity of the system, but in this case there could be some doubt as to validity of such data at 0214z. I understand that the SATCOM phased-array antenna system requires an initial position, altitude, heading and attitude, etc. to seek the nominated satellite, but once "locked on" will become self-sufficient - within reason.
The 0214z "Ultimo Reporté" position - 3° 16' 28"N 30° 22' 28"W used by the Brazilian Air Force (FAB) is right on track and uses the INTOL 0133z and TASIL 0220z times to derive a position for the last known transmission from the aircraft. This is standard Search and Rescue procedure, and the fact that the ACARS position and the "Ultimo Reporté" position share exactly the same longitude, is just one of "long odds" in a lottery.
In fact, there is a difference between the derived SAR position - 3° 19'N 30° 21'W and that plotted above, but as the distance between them is only 2.85NM they have been shown as one. I suspect that the FAB has actually used the same methodology to arrive at their "Ultimo Reporté" position as I have done.
Examination of the Estimated Positions (light blue dots) on the chart above will provide some evidence that the aircraft has either become involved in an overspeed situation, possibly from erroneous air data inputs or from winds associated with strong CB cell sheer. The 0200z position to the 0214z ACARS position gives a Ground Speed (GS) of 502 knots, while the 0210z to the 0214z ACARS position gives a ground speed of 600 knots. If the aircraft had proceeded from INTOL at 453 knots GS, then the 0210z Estimated Position would have been 8.5NM further back on the track. This situation results in 735 knots GS to the 0214z ACARS position! Without knowing at what altitude the aircraft was and the Outside Air Temperature (OAT), it is impossible to draw any conclusions, except to say that events that occured between 0210z and 0214z may have lead to an overspeed incident/accident.
18 June 2009. Since writing the above, the French Accident Investigation Bureau (BEA) has released details showing the positions of recovered debris. The only physical references on the chart published were, (a) TASIL, (b)'derniére position connue' (last known position), and (c) a 50km scale. Extrapolation has provided an 0210z position at 3° 00.3'N 30° 33.3'W. which is about 1.5NM left of track and slightly more than 1 minute ahead of the 0210z Estimated Position. However, a better solution is to use the position provided by the BEA with their Surface and 1000m depth currents. It is 2.98N 30.59W, or 2° 58' 48"N 30° 35' 24"W and the BEA's 'derniére position connue' on the chart has been changed to reflect this new information which is about 3NM left of track and slightly less than 1 minute ahead of the 0210z Estimated Position.
The BEA 0210z position seems consistent with the aircraft having continued from INTOL at Mach 0.82 as per the Flight Plan. However, the "so called" 0214z ACARS position should be discounted completely for the following reason:-
(a) 3.5777°N 30.3744°W = 3° 34' 40"N 30° 22' 28"W - 0214z ACARS
(b) 3.2777°N 30.3744°W = 3° 16' 28"N 30° 22' 28"W - 0214z Ultimo Reporté
- the most significant digit following the decimal in the latitude coordinate was probably changed or mistranscribed from a reporter's notes, and the position provided doesn't fit any "real" probabilities. (See 21 June 2009 update - below).
20 June 2009. The 0148z SSR media reported 453 knots GS now appears to be incorrect, as the BEA have released a flight path graphic showing the recorded position of the aircraft as received by Air France via SATCOM for every 10 minutes from the commencement of the flight out of Rio de Janerio until the last position report received at 0210z. The reported time of 0133z at INTOL as well as the 0148z SSR "final squawk" correlate with the auto SATCOM positions. INTOL to the 'derniére position connue' position is 293NM, which provides a ground speed of 475 knots.
Note:: At these speeds a variation in timing of 1 minute results in positional displacement of 8 nautical miles (15KM), so absolute precision is not easily achieved.
21 June 2009. Assuming that the auto SATCOM position report at 0210z supplied the latitude/longitude coordinates, then without reference to someone in Air France Flight Operations it is only a guess that track, ground speed, flight level and outside air temperature were also sent. That being the case, then 020°T by 570 knots GS leads to the 0214z ACARS position - a position that would never be reached.
In the original write up for Wikipedia (box above), I mentioned the finding of identified debris near 3° 34'N 30° 28'W. This debris, a seat cushion, may well be the best clue as to where a possible in flight break up occured as it has a reasonably large area/volume to mass, and the likely trajectory will quickly become more vertical with increasing air density. More importantly it floats with a low profile to surface wind. Simplistic hydrographic current modelling has already been mentioned above, but careful analysis using observed surface currents along with the SHOM Surface and 1000m depth currents may help provide likely trajectories for larger items and their ultimate locations.
My suspicion is that shortly after the Auto Pilot Disconnect ACARS message, the aircraft was no longer in controlled flight and a high altitude stall now seems more probable, which would most likely result in excessive G forces in an attempt to recover and a resulting airframe break up. The horizontal velocity of the aircraft would now have reduced significantly and wreckage would be confined to a relatively small area - maybe a radius of 15NM. The true cause will not be known until at least the Flight Data Recorder is located and recovered - hopefully intact.
Time taken for bodies to surface would be influenced by the depth of water and temperature. Deep subsurface currents tend to be of a low velocity and tend westerly, but upward momentum of bodies will basically be determined by gas created in the decay process - very slow in deep cold water temperatures and progressively greater as they approach the surface. Many of those bodies already recovered will have been travelling freely in the near to surface current for many days before becoming buoyant enough to become visible on the sea surface. This explains the large distances found between individual bodies, but follows the processes just outlined.
23 June 2009. The position of the Vertical Stabilizer when recovered has been determined with reference to the BEA debris data of 17 June 2009 and a graphic published by the FAB for 9 June 2009 showing the item marked "Grande Peça" at 234°T x 45NM from TASIL. This "Grande Peça" item has been matched up with the BEA debris number 209 and a fairly reliable position of 3° 34'N 30° 36'W, which has now been plotted on the chart above. This position is also west and south of other debris recovered on the same day, and some conclusions may be drawn from this.
Note:: Closer examination of the FAB derived data above, proves that it is totally unreliable (the positions used and distances given do not correlate) and the location has been changed - see 27 June 2009 update below.
27 June 2009. Without being able to conclusively identify the recovery location of the Vertical Stabilizer, a position found for item 209 in the BEA positions of recovered debris on 8 June 2009 has been added to the chart. Suspicion that the Vertical Stabilizer may have a bearing on the incident cannot be ruled out, as the aircraft may well have entered a "micro burst" of high energy upward and outward flowing winds combined with a change in air temperature and saturation as well as density. Violent yawing ("fish tailing") combined with a longitudinal oscillation through the airframe could have been responsible for rapid metal fatigue at the base of the Vertical Stabilizer. Any other events may well be consequential to, or just part of this ITCZ turbulence.
03 July 2009. The BEA in its Preliminary Report on this accident has provided a few more clues as to what may have happened. The appendix documents to the report are to be found only in the French version, and the English language version of the report is available here. It is possible to discount the "forté turbulence" report - it apparently didn't happen. The events that lead to the aircraft impacting with the Atlantic Ocean appear to have their origin at just before 0210z when the aircraft was probably in the most convective part of the ITCZ event, into which it had penetrated.
The Vertical Stabilizer location has now been conclusively identified, and once more the chart above has been amended. Debris item #209 has been left on the chart, and it would seem that items that had any significant windage were carried further to the west than the surface current would normally have taken them. There has also been an addition to the chart which allows the overlay of some meteorological data showing where satellite images detected cloud tops in excess of 50,000 feet. This data shows as pale purple areas, and a notable spot is at the 0210z position. The origin of the data is from the Meteosat 9 satellite and the 'nominal' time of the image was 0215z, though the image area was actually scanned at 0208z. It is reasonable to assume this event was occuring just prior to the initial ACARS messages commencing at 0210z.
Near the bottom left of the chart above there are three radio buttons which will allow you to switch the image either fully on, 50 percent opacity, or off.
Barry Carlson - 7 June 2009