AF 447 Search to resume

[Chris Scott]

Oh bother, I missed that one the other day. But they didn't give much notice, did they? Three days' notice to register. Pity it's too late now; otherwise we could have asked broadreach to take time off for a long day's jolly up to Recife.

[auv-ee]

News stories from today's press conference are starting to appear. This one contributes no new information, but has some nice pictures, including some in the side bar to the right.

Airbus e Air France retomam operação para localizar as caixas-pretas | Últimas notícias | Diario de Pernambuco - O mais antigo jornal em circulação na América Latina

The Portuguese/English translation provided by Google:

Google Translate

says:

On board the vessel will be three mini-submarines REMUS 6000, the same that allowed the location of the wreck of the Titanic.

which is not correct, considering that the wreck was located in 1985; perhaps this is a translation error. However, the REMUS 6000s did visit the Titanic last summer to participate in a survey of the wreck and debris field.

EDIT:

This German article has better technical information and gives the viewpoint from IMF-GOMAR, who are providing one of the REMUS-6000s. I think all of this information is known in this group.

Neue Suche nach vermisstem Air France Airbus

Google Translate

[broadreach]

Thanks for the suggestion, Chris. Fortunately, I missed the BEA release as well or I might have been tempted.

The advantage of Suape over Recife is that it's well removed and a pain to get into, ergo less journalists and other interested parties. Even so, given the size of the Alucia one suspects there would have been little room to swing a cat this morning.

And, as from now on, little fresh news - sans spin - regarding the search is likely to appear unless it arrives indirectly via MM43's or others' contacts.

[mm43]

Information + interpretation = misinformaton

There's nothing more to say!

[mm43]

Update - BEA press release

Information, 23 March 2011

The "Alucia" departed Suape (Brazil) on 22 March, 2011 at 2320z.

Link to press release and BEA video made in Suape.

[mm43]

The following is the English translation of the video commentary.

In a few hours, a final search operation attempting to locate the wreckage of Air France flight 447 will be launched from this harbor, in Suape, Brazil.

A crew of 34 has been deployed for this operation that will last 16 weeks and use 3 autonomous underwater vehicles to locate the wreckage.

The operation is smaller than the last one, but it is designed to cover the search area in 4 months.

Over the last 12 months, the BEA has been adjusting its strategic approach.

Jean-Paul Troadec, Director of the BEA, comments:

"Last time, our strategy targeted a relatively limited area, located in the North West region of the perimeter where we believe the crash occurred. This time, we are going to survey the entire area inside the circle. This was not previously done."

The strategy adopted may be different, but a high level of determination remains:

"This is a really peculiar situation. There are very few instances in which accidents occurred and we were not able to either explain their causes or retrieve flight recorders".

The crew will deploy autonomous underwater vehicles called REMUS 6000, able to operate at depths to 20,000 ft. and navigate over rough terrain. The three vehicles were used at the site in 2010 and demonstrated their effective sonar detection performance and photographic recording abilities.

At the head of this flotilla, Mike Purcell, of the Woods Hole Oceanographic Institution, who is the chief of sea search operations.

Mike Purcell (WHOI) discusses tactical operations:

"We are going to start searching north of the aircraft's last known position, close to the area where last year's operation ended. Survey, in the first leg, will cover unsearched terrain in a circular area extending 20 nautical miles around the last known position. Some areas may prove more difficult to search considering their rough terrain, but we feel very confident about the ability of REMUS' vehicles to find the plane wreckage."

The search operation is under the authority of the BEA. A specifically appointed safety investigator will remain onboard at all times. Airbus and Air France will cover the financial cost of this operation, estimated at $12.5 million.

Jean Claude Vital, BEA safety investigator, comments:

"I will act as liaison between the crew and fellow investigators of the BEA. When we locate the wreckage, I will start identification and validation procedures before moving on to phase #5."

The search could last up to 100 days and extend over 10,000 km^2. The BEA would then dispatch 3 consecutive onboard investigators. Should the accident site be located, the BEA will immediately move on to phase #5, and focus on retrieving the flight recorders for analysis.

[Chris Scott]

Everyone hopes that part or all of Charlie Papa's remains will be found this weekend or soon after, but we have to continue to be realistic. The BEA is interestingly vague about the deadline of Phase 4.

"The search could last up to 100 days..."
"... this operation... will last 16 weeks [112 days]..."
"The operation... is designed to cover the search area in 4 months [~122 days]."

Fingers crossed it doesn't come to that.

[Bobman84]

Hope they find it this time. I'm really curious how complete the plane might be or what exactly happened as is everyone else.

Wish them all the luck.

[mm43]

The "Alucia" has arrived in the proposed search area, and my interpretation of press releases is that the search will commence in the north sector of the 20NM radius circle and progress southwards. A reposting of a previous BEA graphic with additional enhancements will provide a general indication of the area the "Alucia" will now be working in.



EDIT :: For clarification, the yellow circles are drawn at multiples of 10NM radii from the Last Known Position. The initial Phase 4 search is concentrating within 20NM radius of the LKP, and the remaining area out to 40NM will eventually be searched if required.

[Capetonian]

I don't know how you professionals will view this article, but I think it explains well in laymans' terms some theories that have done the rounds.

Aviation accidents: The Difference Engine: Wild blue coffin corner | The Economist

[auv-ee]

WHOI Press Release

Last week WHOI issued a press release that provides some additional technical detail that has not appeared accurately before.

News Release : WHOI Conducts Latest Search for Air France Flight 447 : Woods Hole Oceanographic Institution

It says that BEA plans to issue weekly updates.

[mm43]

Capetonian

One of the better newspaper articles on the subject. Readable and without any wild assumptions about what did or didn't happen.

The readers comments show the full range of opinion, misconstrued or otherwise.

[Chris Scott]

I was also impressed. In general terms, the description of flight at subsonic-jet cruising altitudes is remarkably well-informed by journalistic standards, including the part about coffin corner. Well above average.

17000m is normally on the high side for the tropopause, even in the tropics (was it that high for AF447?). The quoted 25-knot envelope at 10600m (FL350) seems about right, provided you are considering IAS rather than TAS. That doesn't represent most pilots' idea of being close to coffin corner.

[HazelNuts39]

Facts

At the time of the accident, AF447's "coffin corner" was at FL460. Shortly before that, the airplane was in cruise at FL350, M.82 (280 kCAS). The available range of safe speeds at that altitude was from M.58 (192 kCAS) to M.86 (295 kCAS). It would take 2.5 minutes to decelerate from M.82 to M.58, the low-speed boundary for the onset of perceptible buffet, in level flight at zero thrust, and somewhat longer at idle.

Regards,
HN39

[mm43]

17000m is normally on the high side for the tropopause, even in the tropics (was it that high for AF447?).

Possibly a handwritten 1 has been transcribed as 7.

...m.......ft......°C
10999 36089 -56.3 ISA at tropopause
10668 35000 -54.1 ISA (AF447 - forecast -46°C)
09448 31000 -46.2 "

[Chris Scott]

Thanks for the AF447 specifics, HN39,

I am reminded that the 25 kts envelope I was thinking of has MMO at the top end and VLS at the bottom. At this late hour (and the wretched clocks about to go forward from real time to big-brother summer time here) I'm not going to try and look up the definition of VLS in the cruise; but it is way above the 1g buffet, of course. Of the order of 1.3g?


Thanks for the AF447 trop figure, mm43,

It's remarkably low for the tropics, considering that the standard atmosphere uses 11000m (36090ft) -56.5C, (and tends to represent temperate latitudes) - almost exactly the same. There could have been a very big step-up at the frontal ("ITF") edge, I suppose?

[HazelNuts39]

Chris;

VLS in the cruise is probably(*) defined as 1.3 g to buffet onset, which is M 0.675 (226 kCAS) for AF447.

According to Tim Vasquez' analysis, the tropopause level was 15295 m. What is the importance?

Regards,
HN39

PS:: (*)Buffet onset varies with C.G., while the stall speed (Vs1g, V-alphamax) per regulatory definition is at forward C.G. (17%). I don't know what convention Airbus uses for VLS in the cruise with respect to C.G. My values are for C.G.=37%.

[Chris Scott]

Sorry, HN39,

I'm unable to say whether the displayed VLS allows for cg position, or how much difference it makes. The FMGC certainly calculates where the current CG is, expressed in terms of %MAC (mean aerodynamic chord), but relies on correct crew entry of the ZFW CG. I don't know if there is any independent in-flight verification of current CG.

[In the case of current AUW (gross weight/mass), the FAC (not sure if it's called that on the A330) calculates current AUW independently of the FMGC (so if the crew enters the wrong ZFW before departure, the assumed AUW is not grossly affected).]

By the way, for anyone puzzled, 1.3g is equivalent to a balanced turn with 39 degrees bank. Flying at the 1g-buffet speed is for test flights only. As HN39 indicates, the true "coffin corner" is where the 1g-buffet speed equals MMO [see Editorial Correction below]. Fortunately, very few aircraft (and certainly no airliners) have enough high-altitude thrust to get up there. Flying "on the 1.3g buffet" is fine if you are in reasonably smooth air, and not planning on using more than about 15 degrees of bank.


Quote:
According to Tim Vasquez' analysis, the tropopause level was 15295 m. What is the importance?

I think it is important, and that is very different from the figure (10999m) quoted by mm43.

Flight in the vicinity of a clearly-defined tropopause ("trop.") ** is an unsettled affair. (For the uninitiated, met books traditionally described climb above the trop. as being isothermal; in practice there is a distinct rise in temperature initially as you climb through it.) In level flight, every time you encounter the mixing layer, the SAT (and therefore TAT) go all over the place, affecting IAS and IMN (indicated Mach), the engine thrust changes spontaneously, and the W/V changes. If they had been cruising in and out of the trop., they would have been in that regime. Also, they might have been in and out of the tops of Cbs. (Again for the uninitiated, the trop. acts like a saucepan lid, because of the inversion of temperature associated with it.) That itself is uncomfortable, but unlikely to be accompanied by icing/precipitation.

On the other hand, if the trop. was over 4000m above them (typical in those latitudes), the regime would have been very different. Better in terms of stability away from Cbs; but in the midst of the cells if they entered Cbs. That means severe turbulence, probable precipitation with icing, and high risk of lightning strikes.


** "Trop." is flight-crew slang for "tropopause", and is not to be misinterpreted as meaning troposphere, which is the volume of air between the tropopause and the earth.

[Editorial Correction]
Following HN39's post #2842, the sentence highlighted in red is amended as follows:
"The true 'coffin corner' is the altitude at which, flying at 1g, the onset of the low-speed buffet occurs at the same speed as the onset of the high-speed buffet. In this case, the high-speed buffet occurs at a speed below MMO."

[Dengue_Dude]

Who pays for this extra search, come to that, who's paid up to now?

[auv-ee]

Originally Posted by Dengue_Dude

Who pays for this extra search, come to that, who's paid up to now?

The present search (Phase 4) is funded by Air France and Airbus, probably equally.

The Phase 3 search (Spring of 2010) was also funded by AF and AB.

I'm not sure who paid for the Phase 2 sonar search by the Pourquoi Pas? in August of 2009.

The Phase 1 search, immediately after the accident was likely paid for by several governments, mainly France and Brazil.

If the site of the wreck is found, then there will be a Phase 5 recovery that will be paid for by France through BEA:

The New Undersea Search Campaign

I'm sure others will correct or clarify any of this.