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AAIB BA38 B777 Initial Report Update 23 January 2008

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AAIB BA38 B777 Initial Report Update 23 January 2008

Old 2nd Feb 2008, 13:49
  #241 (permalink)  
 
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Anyone who still believes that RFI does not affect electronic systems, please take a look at this:

http://www.cherryclough.com/Download...20Oct%2005.doc

(Word doc format)

Whilst most of the examples given are not directly aircraft related, it clearly demonstrates the wide range of effects RFI can have on an electronic system.

Some sort of high powered transmitter, operated near an aircraft *could* adversely affect avionic systems.

(Note that I said "could" and not "will", "would" or anything similar)
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Old 2nd Feb 2008, 14:12
  #242 (permalink)  
 
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Anyone who still believes that RFI does not affect electronic systems, please take a look at this:


If Radio Frequency Interference didn't affect electronic systems it wouldn't be called Radio Frequency Interference - would it.
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Old 2nd Feb 2008, 15:19
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Aircraft such as the B777 are tested against HIRF (High Intensity Radio Frequency) and critical areas such as the Main Equipment Centre of this aircraft is shielded against it (you only have to look at the SRM for this).

Systems such as flight controls and other rated as critcal are qualified against RF levels up to 200 volts per metre and taking into account the far field square law for RF attenuation (as you double the distance, you half the power), you would need something big and powerful to affect an aircraft at any altitude. For example, the RADAR tower at LHR will be pushing out a fair bit of energy and this is less than a few hundred metres away from aircraft.

This is not RFI/EMI/EMC related incident IMHO
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Old 2nd Feb 2008, 15:26
  #244 (permalink)  
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Not RFI

Agree this is not due to RFI, just think about the RF environment at any Airport. Radar, Comms, Navaids, Mobile Handsets, Walkie talkies etc. If it was that easy to bring down a modern aircraft they would be crashes at every airport. Plus the Military would be looking at it for AA uses!
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Old 2nd Feb 2008, 16:17
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Yes, all aircraft are tested. However, it is impossible for the tests to cover all eventualities.
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Old 2nd Feb 2008, 17:20
  #246 (permalink)  
 
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Known RFI versus Hostile RFI

Quote from Whatisthematrix (today, 15:19):
Aircraft such as the B777 are tested against HIRF (High Intensity Radio Frequency) and critical areas such as the Main Equipment Centre of this aircraft is shielded against it (you only have to look at the SRM for this).
[Unquote]

Thanks, Whatisthematrix, those of us waiting to fly it were naturally very concerned about this when the A320 was being certificated, 20 years ago, in 1987/8. But I'm not sure that hostile RFI was on the engineering agenda in those days, or even the B777's.

Just to correct your (unintentional?) slip, the signal strength is quartered, not halved, at double the distance. [As you say, signal strength is inversely proportional to the distance SQUARED.] That's why my proposed transmission would need to be so powerful.

I've experienced small high-frequency control oscillations from the AP during my own routine HF R/T transmissions on a big jet in the 1980s (pre-FBW technology). Typically, the omni-directional antenna is in/on the fin (vertical stabiliser).

A legitimate HF antenna (for comms) on an aeroplane may be as little as, say, 3 metres from a rudder control servo. But the nearest digital computer of the FADEC/EEC variety might be as much as 30 metres away. Any shielding has comfortably to cope with that. To replicate that signal strength from a ground antenna 300 metres away, it would appear that 100 times the transmission power would be required, but this applies only if the illumination is omni-directional.

So the transmission has to save power by being directional. ATC surveillance radar is directional (in azimuth, at least), as you point out. But, if I remember rightly, radar operates on SHF between (roughly) 3GHz (10cm) and 10 GHz (3 cm), at moderate power, with a BIG receiving dish.

I'm thinking more at the other end of the scale: LF (30KHz - 300KHz) or VLF (< 30KHz). I am minded that the military have used some powerful transmitters in the past, for long-range (directional?) comms. Perhaps someone could enlighten us?

Last edited by Chris Scott; 17th Feb 2008 at 15:03. Reason: Change of other post ref #s
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Old 2nd Feb 2008, 22:34
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Adjective
adequate (comparative more adequate, superlative most adequate)


Equal to some requirement; proportionate, or correspondent; fully sufficient; as, powers adequate to a great work; an adequate definition lawfully and physically sufficient.


What part of adequate is rather vague?
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Old 2nd Feb 2008, 23:20
  #248 (permalink)  
 
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FE Hoppy

"adequate"?
I know very well what the word means!

I do not mean that "adequate" is a vague statement - what I mean is that "an adequate fuel quantity" is a vague statement - I apologize for my mistake

I still would like to know the remaining fuel onboard upon landing - just for info.

I flew the B-767 for many years, and on long flights, especially to our homebase we some times had to replan without fuel to alternate - i.e. land with final reserve fuel (on the B-767 2.0T) as absolute minimum.
Of course weather etc.. permitting.

I just wonder if BA038 did so on their lucky day!

Last edited by grebllaw123d; 2nd Feb 2008 at 23:30.
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Old 2nd Feb 2008, 23:21
  #249 (permalink)  
 
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The AAIB promised more updates as and when, it is about time that we had more info on the progress of the investigation. Even though they cannot pinpoint the exact cause at this time they could well, hopefully, destroy many of the speculative theories expressed in these august posts. I know from personal knowledge that they have brainstorming sessions with all of the inspectors at Farnborough expressing all of the likely reasons for the accident, and they then set about eliminating each likely cause until they find one that cannot be eliminated. I am seriously concerned that they are not going to find a definite cause for the lack of demanded engine thrust from both engines.
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Old 3rd Feb 2008, 09:58
  #250 (permalink)  
 
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AAIB

Stuart

See post #230 by Gem Developer. I think that gives a fairly rational explanation of why AAIB is waiting until all the tests are in.

Pinkman
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Old 3rd Feb 2008, 17:38
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Post 263
Recorded data indicates that an adequate fuel quantity was on board the aircraft and that the autothrottle and engine control commands were performing as expected prior to, and after, the reduction in thrust.
My reading of this statement is that the AutoThrust/Engine Controls (Throttle Levers?) were working as expected however this statement does NOT explicitly state that appropriate commands were transmitted from the FADEC/EEC to all of the boxes e.g. Fuel Management Unit FMU etc that take their commands from the FADEC/EEC

FWIW My limited experience in these matters suggests that it is not what is said but rather what is NOT said that is significant.
Stuart
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Old 3rd Feb 2008, 18:15
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What would happen if the tank fuel temperature sensors overread?

The crew would be blissfully unaware while the wax crystals accumulated to the point where little more than flight idle was available.

They would get the bad news when more thrust was needed.
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Old 3rd Feb 2008, 18:23
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What would happen if the tank fuel temperature sensors overread?

How many separate/totally independent fuel tank temperature sensors are fitted in the 777 tanks?

S
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Old 3rd Feb 2008, 18:47
  #254 (permalink)  
 
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I have nothing new to say on the 777 incident per-se but do have an observation nonetheless...

Every accident or incident gets people chatting about possible causes and chains of events. Much of this is no doubt drivel and some of it may well be spoken by experts with every shade in between. Some think this speculation is a bad idea and think we should say nothing until the AAIB reports. I beg leave to differ.

To me the debate may well go down a good many dead ends and contain many inaccuracies but surely those who know better will correct those who have blundered and all will learn from the experience, whether or not the board outcome is accuratly guessed. I would far rather see a exchange of ideas that ultimatly raises the profile of the issues at hand and improves understanding than have silence until the AAIB report their findings.

Good pilots are always seeking to learn from the mistakes of others and will also seek to 'try out' their pet theories, if anything to expand and validate (or otherwise) their understanding - IMHO it can only be healthy provided everyone keeps an open mind.
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Old 3rd Feb 2008, 18:57
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What the AAIB are not saying

Snanceki - I agree that the wording of the first update reads as if it was meant to be very precise indeed, I was just curious to see if anyone could throw more light on just what they did mean. I thought 'engine control commands ' had to refer to all of the engine control systems but I can see there may be components that are not coverd by the term.

Once the immediately obvious stuff of gross error and fuel exhaustion were out of the way, this accident was always going to be tough to explain, aircraft of this sort are just not meant to suffer double failures. I agree with others, though, the AAIB implied they would keep the community informed as and when, but they haven't done so. No idea what this implies. It was suggested that they wouldn't want to even mention fuel contamination for political reasons, in order not to upset the Chinese; I'm not sure what that would achieve, as contamination has to be up there in the frame as one of the relevant common modes in the system, and it has been a prime suspect and hot topic as a result. I recall the Big White Chief was quoted as saying that there would be a report in 30 days, the clock is ticking.
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Old 3rd Feb 2008, 21:49
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What the AAIB are not saying..

gonebutnotforgotten - you say:
"aircraft of this sort are just not meant to suffer double failures."

In a sense you are right, aircraft are not meant to suffer double failures, but nevertheless double failures MAY occur in old as well as in modern aircraft, although the risk is extremely small.

I am not saying that we have a double failure of some sort in connection with this accident - but nothing can be discounted
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Old 3rd Feb 2008, 23:09
  #257 (permalink)  
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Crossfeed valves

The FAA "leak" says
The fuel crossfeed valves were closed in flight according to the flight crew, but the switches were found in the open position and only one valve was open. In the days following the event, the flight crew has added additional details to their report. The crew now believes they opened the valves just prior to impact and the airplane lost power before both valves moved to the open position.

It sounds as if there was a common feed to both engines, and that something in the right tank interfered with the flow to both engines.
 
Old 4th Feb 2008, 04:31
  #258 (permalink)  
 
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If every checklist fails to make things work, I would open crossfeeds, do anything to help the situation no matter what the checklist says and doesn't work. Especially like this when you have no time to read a checklist. They were probably thinking outside the box because that is all they had left. If he brought the flaps up to 20 he probably saved everybody but no checklist says to do that at 600 ft. He did a great job.
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Old 4th Feb 2008, 05:28
  #259 (permalink)  
 
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All will be likely answered in the next update.

Bubbers44:
After reading that internal report, this is exactly what I thought - when your givens are gone, get creative.
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Old 4th Feb 2008, 08:31
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Hmmm.

@GerryFoley
Crossfeed valves
The FAA "leak" says
The fuel crossfeed valves were closed in flight according to the flight crew, but the switches were found in the open position and only one valve was open. In the days following the event, the flight crew has added additional details to their report. The crew now believes they opened the valves just prior to impact and the airplane lost power before both valves moved to the open position.

It sounds as if there was a common feed to both engines, and that something in the right tank interfered with the flow to both engines.
Hmmm.
How did you conclude the "....right tank interfered with..." bit?
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