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Old 24th Apr 2011, 23:56   #61 (permalink)
 
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ALCS65, they went down 400 miles from Natal (which I'd half expect to be VHF ACARS equipped and 160 miles from Fernando de Noronha (which might be ACARS equipped.) They were pretty much out of VHF communications for quite a period of time. Off hand I cannot find a reference to either of them supporting ACARS. I'd estimate they were a good hour out from any meaningful VHF contact, maybe (much) more. I'd expect the cut over to satellite would happen at or some modest time after the switch from VHF flight control communications to HF.

Released documentation reports the last several position reports as well as the standard ACARS all, they say, through Inmarsat's AOW bird.
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Old 25th Apr 2011, 00:43   #62 (permalink)
 
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Electromagnetic messaging from aircraft

I get the impression that some commentators here are making the assumption that HF/VHF/UHF radio signals from AF447 would have been equivalent to that of trailing a broadband internet cable behind the aircraft.

Radio amateurs would love to have an antenna 40,000 feet up in the air but realize that in the midst of an electromagnetic storm, signals even 500 metres away might be unintelligible to a receiver due to noise, propagation anomalies and polarization rotations regardless of error correction protocols even if one is dumping the full American 1.5 kW into the ether.

Does anyone know if the QRN at the critical moments of the AF447 flight obliterated RF communications or whether the sequence of the ACARS messages was affected by poor reception?

Last edited by kilomikedelta; 25th Apr 2011 at 01:23. Reason: clarification
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Old 25th Apr 2011, 01:23   #63 (permalink)
 
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Quote:
Originally Posted by Greybeard
I have great respect for Public Broadcasting in the US, but this program failed miserably. I wonder if major sponsor, billionaire David H. Koch, didn't have too much editorial input?
One might fault PBS for repeating without independently checking, but that was originally a BBC production broadcast in the UK on 2010/05/30. I believe it was re-narrated (different accent of narrator) and possibly re-edited for the PBS release on 2011/02/16.
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Old 25th Apr 2011, 01:41   #64 (permalink)
 
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Quote:
1. The storm did not look bad enough to deviate around.
2. The line of storms was so long and uniform, it would not seem to matter where they penetrated.
3. The pilots did not have enough training in Wx radar ops.
. a. Nobody was looking at the radar returns.
I believe 1., 2. are more likely than 3. or 3a. The whole WX deviation thing may be a red herring. In the animation that PJ2 posted, we can see the ELY flight flying without any deviations. In fact, it looks like it flew through a cell comparable to the one AF447 is projected to have flown into.

I think AF447 was unlucky to have entered a UAS condition. (quite independent of weather conditions.) AF knew this was always a possibility, no matter how remote. Hence, the pitot replacement program.

Two other possibilities I'd like to add to the above list, if I may:

4. Crew noticed something anomalous with airspeed and were fixated on understanding the situation.

5. Crew noted the weather ahead but deemed it a lower priority issue than something else. (If so, what is the USD 64K question)

Quote:
But the pilots would know that NORMAL LAW is u/a, so why try to latch a/p only to see it booted (rejected) by the computer again??
Could this be the last actions of a crew desperate to get out of it...
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Old 25th Apr 2011, 01:45   #65 (permalink)
 
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Brazil - VHF ACARS

Most of Brazil is covered by SITA/Datacom VHF ACARS, and the eastern corridor is completely covered. This coverage extends to a station located on the offshore island of Fernando de Noronha (SBFN). The ACARS frequency is 131.55MHz, and this coverage was in place at the end of 2008.

AF447 was in range of the SBFN secondary radar until about 250NM or about 10 minutes after passing INTOL. With an omnidirectional 3dBi VHF antenna at SBFN, reliable data comms should have been achievable to at least 180NM with the a/c at FL350.
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Old 25th Apr 2011, 01:57   #66 (permalink)
 
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"With an omnidirectional 3dBi VHF antenna at SBFN, reliable data comms should have been achievable to at least 180NM with the a/c at FL350."


In HF/VHF/UHF in the middle of a Cb?
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Old 25th Apr 2011, 02:25   #67 (permalink)
 
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ARINC assumes a coverage of about 245nm for an aircraft at FL300. Both Natal (NAT) and Fernando de Noronha (FEN) are ACARS RGS's, but I put NAT at 590nm and FEN at about 420nm.

It does look like AF447 would have passed through several VHF ACARS sites prior to being out of range. Still hoping someone with first hand knowledge can comment on whether the VHF to SATCOM ACARS switch happens automatically as mentioned in the manual, or if maybe on a flight on this route it just uses SATCOM the whole time.

RGS List:
RGS list
(Note: Not a complete list.)

Map:
http://datalink.sas.se/ground/images/sita_eumea.pdf

Quote:
ALCS65, they went down 400 miles from Natal (which I'd half expect to be VHF ACARS equipped and 160 miles from Fernando de Noronha (which might be ACARS equipped.) They were pretty much out of VHF communications for quite a period of time. Off hand I cannot find a reference to either of them supporting ACARS. I'd estimate they were a good hour out from any meaningful VHF contact, maybe (much) more. I'd expect the cut over to satellite would happen at or some modest time after the switch from VHF flight control communications to HF.

Released documentation reports the last several position reports as well as the standard ACARS all, they say, through Inmarsat's AOW bird.
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Old 25th Apr 2011, 02:28   #68 (permalink)
 
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Thanks for getting me to dig into the books again, mm43. Yes, tangential range is 300 miles or the equivalent in nm. Intelligibility would likely suffer some at about 200 miles. They were easily out of communications for some time before things pickled.
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Old 25th Apr 2011, 02:32   #69 (permalink)
 
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kilomikedelta - at 200 miles out they were not in a storm. That came up 200 miles further on. And the map I checked distances on had the LKP mislocated. They had it south rather than north of the equator. Teach me to double check things rather than wing it.
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Old 25th Apr 2011, 03:59   #70 (permalink)
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Salute!

Too much about ACARS and WX radar on the jets. And times for ACARS data not correlated with the flight recorders yet.

As Cog pointed out, at least one other plane flew thru the wx.

SOMETHING happened and the result was loss of control. I do not blame the crew.

I have flown thru the ocean CB's and they are nothing compared with a big CB over Kansas, USA. Whatever happened was before penetration of a line of storms. I use the Captain's body recovery to make the point that "things were going well until......"

Before I quit posting here for awhile, I shall bet that some sensor or input to the flight control system went haywire and the crew could not figure it out in time to do something constructive. My God, I just went thru the tech order for the jet and it is layer upon layer of inputs to the control system. Sheesh. Despite the plane's basic aero stability compared to the military jets that have FBW, it looks like even the most basic control laws still use many inputs from sensors. And some of those could be FUBAR.

The CVR will be more revealing than the basic flight data recorder, IMHO.

What did the crew see?

What were the flight conditions? When things went south, what was the environment? Were they pitching up and down and rolling left-right? I don't think so or the Captain would have been back in the cockpit.

SOMETHING happened before encountering the storms. The ACARS transmissions will soon be correlated with the flight recorders. We may be able to paint a picture of the final minutes or seconds. Findings will help to prevent another occurrence.

Although the Columbia breakup did not capture much crew talk, the flight dynamics were faithfully recorded. That tragedy took place very quickly despite indications on the recorder that something was terribly wrong 4 or 5 minutes beforehand. The crew didn't know, but at the last transmission they wanted to ask about something versus tire pressure in one of the wheels that the ground control was interested in.

sorry for the rant, and will stay silent for a bit.

P.S. The IAF guy on board Columbia was a student of mine in the F-16. I have a patch from that IAF bunch, and the IAF only sent one small group to check out in the first operational FBW jet in the world. So I have a special interest in incidents involving FBW planes, having been one of the first to fly the damned things.
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Old 25th Apr 2011, 04:55   #71 (permalink)
 
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Hi, KMD this is CW,

With the proper selection of QRG (band) HF would be VERY RELIABLE even with high QRN and the poor current HF antennas.

I NEVEER lost a QSO in several thousands hours of HF operation using 200 W out sometimes lowering to 1.8 MHz (phone) due severe QSB.

In just one case due a VERY STRONG WX System i faced almost complete blackout of powerful MW BCST STN 80nm from my PSN but this is RARE.

I don´t believe, based in ACARS msg´s, they tried to use comm, HF or other.

They should be looking to other priorities.

The info on QRN at the night i think was lost and i think was not a factor.

On good antennas look at the trailing wire (30,000 ft) used by the 707 of USN for VLF to subs.

Unfortunately the current HF antennas are VERY POOR.
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Old 25th Apr 2011, 05:03   #72 (permalink)
 
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ok do I have this right?

A working scenario is - the FMC disables the autopilot because of unreliable airspeed measurement by the clogged pitot tubes. Once that is done, it should not be possible to re-engage the autopilot manually. Since that apparently did happen, the implication is that the crew re-engaged the autopilot after some initial upset, and this played right into the trap that was mentioned by the recent AD. The crew think they have recovered, and instead they have guaranteed the worst sort of stall, a flat spin basically.

So all talk about being asleep and weather and all that is just not relevant - because the problem here was systemic, even down to the over-reliance on programming instead of piloting. Ok that was a speculation.
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Old 25th Apr 2011, 05:10   #73 (permalink)
 
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JD-EE;
Quote:
Yes, tangential range is 300 miles or the equivalent in nm. Intelligibility would likely suffer some at about 200 miles.
260NM and 174NM.
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Old 25th Apr 2011, 05:23   #74 (permalink)
 
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RR_NDB:
Quote:
Unfortunately the current HF antennas are VERY POOR.
What basis do you have for that statement, Mac?
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Old 25th Apr 2011, 05:28   #75 (permalink)
 
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Appreciate the apology Svarin - accepted.

OK. If I understand correctly, several of you are thinking:
1. Initial UAS leading to upset, leading to loss of AP
2. Manual recovery
3. Re-engage AP - at a lower altitude and several minutes later
4. Catastrophic LOC due to inappropriate pitch up issue covered in recent directive.

Now if you had a significant upset followed by a recovery, would you not expect over a period of some minutes:
1. Some form of radio communication
2. Pax and CC secured

Or do you suppose that the initial upset was sufficiently violent that anyone not secured was incapacitated (and stayed unsecured)? In which case, would the pilots really try and re-engage AP having gained a degree of manual control?

Am I misunderstanding you all here?
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Old 25th Apr 2011, 06:30   #76 (permalink)
 
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'But the pilots would know that NORMAL LAW is u/a, so why try to latch a/p only to see it booted (rejected) by the computer again??'

So if it couldn't/didn't get the a/p back, what was Svarin's ACARS message about ?
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Old 25th Apr 2011, 06:41   #77 (permalink)
 
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Quote:
1. Initial UAS leading to upset, leading to loss of AP
2. Manual recovery
3. Re-engage AP - at a lower altitude and several minutes later
4. Catastrophic LOC due to inappropriate pitch up issue covered in recent directive.
That's one possibility according to the AD.


The other is:
1. Initial UAS leading to upset, leading to loss of AP
2. Manual recovery
3. FD bars re-appear
4. Catastrophic LOC due to following FD orders
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Old 25th Apr 2011, 08:22   #78 (permalink)
 
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Short sequencing of a likely scenario

Gentlemen,

here is my own offer of a scenario sequence. All of this to be taken as an opinion. I would not bet my life on it, but it is the best I could come up with, with great outside help :

1 - high altitude ice crystals (outside CBs but inside thin layer of high altitude clouds around them - red returns on infrared satellite pictures).
2 - ice crystals block pitot probe drainholes (over-reading of IAS)
3 - Unreliable airspeeds -> A/P kicks OFF, along with other stuff
4 - a nasty invisible trap is set through FCPC2, no notice to the crew
5 - crew recovers from UAS without any upset
6 - UAS appears over, F/D bars reappear (see AD)
7 - crew reengages A/P, thinking the problem over
8 - trap is sprung, A/P kicks OFF again in violent upset (hard pitch-up)
9 - upset is not recoverable or not recovered (I expect 99.9% of airline pilots to fail that one)
10 - upset ends up as a deep stall or slow spin to the surface

This means the a/c likely did not crash right after end of ACARS sequence. The Cabin Vertical Speed message looks (to my opinion) like a consequence of FMGEC1 fault triggering a CPC reset or change of configuration, not a real descent (other messages exist for relief valves and other conditions).

Comments, questions and counters welcome.
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Old 25th Apr 2011, 10:01   #79 (permalink)
 
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I've been trying to imagine the mechanism by which re-engagement of the autopilot at corrupted airspeed would cause a violent upset. The AP controls altitude, so the first assumption one needs to made is that the altitude at re-engagement differs from the selected altitude. Let's assume it is lower. The AP will then command movement of the elevator control to initiate climb to capture the selected altitude. The AD suggests that the initially commanded movement of the elevator could be too abrupt when the real speed of the airplane is much greater than what the AP 'thinks' it is. The response of the airplane would then be more abrupt than what the AP is trying to achieve, which is, I suppose, a schedule of vertical acceleration and vertical speed. Wouldn't the AP adjust its command before it results in an uncontrollable attitude?

Last edited by HazelNuts39; 25th Apr 2011 at 10:42.
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Old 25th Apr 2011, 10:07   #80 (permalink)
 
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Goodness.

ELY 010 was on a parallel track to AF447. AF 447 was on Airway UN873. ELY was on UN866, over 100 NM to the west.
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