Nimrod crash in Afghanistan Tech/Info/Discussion (NOT condolences)

[philrigger]

If I may add.

According to MOD Manual; Fuels, Lubricants and Associated Products,
Def Stan 01-5, Issue 15, March 2007

NATO F-34 AVTUR-FSII Def Stan 91-87
TURBINE FUEL, AVIATION: Kerosine type with FSII
and
NATO F-35 AVTUR Def Stan 91-91
TURBINE FUEL, AVIATION: Kerosine type


Flash point, closed cup, min ... ... ... 38 degrees C

Does this help? Probably not.






'We knew how to whinge but we kept it in the NAAFI bar.'

[EdSett100]

SPHL:

I'll revisit this point. But while I'm away, could someone repeat the estimated temperature of the bleed air in the ducts.

Good question. Except during ground starting only (see below) the bleed air is at ambient temperature, where the ducts are outside of the engine fire zones. Inside the engine fire zones (where there are hot gas leak detectors, firewire and extinguishers) the air inside the ducts can reach 500C and 288psi at max engine rpm. I suggest that this is not unusual in any modern aircraft where air is ducted to start the engines.

During ground starts, when we have to open the crossfeed duct, the engines are all kept below 80% by the pilots, which prevents the bleed air reaching more than 150C, which is well below the auto-ignition point of both hyd fluid and fuel.

Regarding the flash point: OK, I was approx 7 degrees out, but I don't normally have my Def Stan book of fuels at home. My thanks to Phil Rigger for the accurate info to keep us on a factual path.

I'm looking forward to reading SPHL's views on the flash point of kerosene vapours.

Regards
Ed Sett

[SirPeterHardingsLovechild]

Wait no more!

http://en.wikipedia.org/wiki/Flash_point

You'll notice I queried your

Kerosine vapour will spontaneously ignite (flash point) at approx 45C.

But we both now know that the 'Auto-ignition temperature' is not the same as the Flash Point

Therefore:-

Kerosine vapour will spontaneously ignite at approx 220°C (428°F)


On the C130, 14th stage (bleed) air can be up to 125psi at 635°F according to Lockheed.

[dodgysootie]

SPHL,
you said:-

"On the C130, 14th stage (bleed) air can be up to 125psi at 635°F according to Lockheed."

Forgive my ignorance, but wtf has this got to do with the Nimrod?

DS

[SirPeterHardingsLovechild]

Wait your turn, and mind your language.

[Distant Voice]

EdSett100: You said,

Oh, they were not. The only facts that were examined, and were availailable, were the ones that the coroner wanted to examine

I am sorry, this is far from the truth, the coroner examined all paths, and if anyone presented delays it was MoD. If there was a problem with "selective" evidence it came from the BOI. Whilst it was agreed that they did did a 1st class job, the evidence was drived by a preconceived ideas as to what caused the accident.

If you were not at the inquest do not attempt to put yourself in the mind of the coroner.

By the way, have you read the Oct 2007 QinietiQ report. Get back to me when you have.

DV

[tucumseh]

Mileandahalf

Come on, everyones entitled to an opinion. Even Min(AF) admitted this when he wrote saying my opinion that provision should be made to maintain aircraft in an airworthy condition was not shared by ANYONE ELSE in the MoD.

I maintain I was right, but while he was wrong it would seem he was only slightly wrong.




We should be aiming at that level, not at each other. (Assuming you are not Adam Ingram).

[Distant Voice]

EdSett100; Please tell us, what facts were not examined. Did MoD withhold evidence? Think long and hard before you answer that one.

DV

[Distant Voice]

Mileandahalf: I can assure you that my views are closer to the true that you can imagine. EdSett100 is making comments based on selected information.

I say the same to you, come back to me when you have read the reports.

DV

[JFZ90]

DV, what are you implying from the posts above & the QinetiQ reports? Are you saying that electrical ignition risks are infact an issue here?

[Softie]

DV states:

If there was a problem with "selective" evidence it came from the BOI.

This is an offensive statement. The BOI took many months looking at all possibilities and delving into the possible causes of this tragic accident. Nothing was excluded when it came to reporting the "facts". From reports, it would appear that some important information/facts were overlooked by the coroner in his short 13 days of focused questioning. Excluding BOI members present from contributing and clarifying was a mistake.

[Distant Voice]

JFZ: Simple answer, yes.

Softie: Please tell me, what important facts were overlooked by the coroner. I know that the "tea stain" track was overlooked by the BOI along with the non-activation of the temp probe in No. 7 tank dry bay area. Waht else do you need to know.

DV

[Softie]

DV. Sir. Neither point you list was missed. As you will never be satisfied, there is no point offering anything to you to trash around in this pointless discussion thread. Let it rest and please get on with your life.

[JFZ90]

"Principally, the key factor in the Very High and High risk assessments has been the proximity of a hot surface relative to the fuel system.....It is considered that these areas of risk are addressed as part of ongoing inspections or aircraft limitations, specifically, limited use of bomb bay heating, HP Bleed Air cross feed and the SCP"

Have QQ changed their view from that above now? If so in what way - what are they now saying?

the non-activation of the temp probe in No. 7 tank dry bay area

What is the significance of this?

"tea stain" track

I guess from some other statements above this issue casts doubt on the "venting after AAR" theory in the BoI. Can someone explain exactly how this was preseneted & what it means - does it rule out the "venting" theory completely or is it still a possibility & hence ultimately inconclusive either way?

[EdSett100]

DV,

EdSett100: You said,

Quote:
Oh, they were not. The only facts that were examined, and were availailable, were the ones that the coroner wanted to examine
I am sorry, this is far from the truth, the coroner examined all paths, and if anyone presented delays it was MoD. If there was a problem with "selective" evidence it came from the BOI. Whilst it was agreed that they did did a 1st class job, the evidence was drived by a preconceived ideas as to what caused the accident.

If you were not at the inquest do not attempt to put yourself in the mind of the coroner.

By the way, have you read the Oct 2007 QinietiQ report. Get back to me when you have.

EdSett100; Please tell us, what facts were not examined. Did MoD withhold evidence? Think long and hard before you answer that one.

DV

At the top of your next post after you have read this, I would like you to correct your error in quoting my words in Post 939. Your version of what I said could indicate that not all the evidence was made available to the Coroner. You must have another look at what I wrote, which is:

The only facts that were examined, and they were all available, were the ones that the Coroner wanted to examine.

I think you will agree that there is a world of difference between what I actually wrote and what you have "copied" that I wrote. So much so, that even you have suggested, as a consequence of your mis-quote, that MOD held back evidence and that "I should think long and hard before I answer." Perhaps you should think long and hard before you answer ;-) Anyway, moving on... and our discussion about selective use of evidence:

Despite being informed by the Staneval air engineer, the air eng on the flight itself, the ground eng who saw it in after flight, that the No1 tank blow off valve did operate on XV230 2 weeks before the accident, and being further informed by the staneval eng that, despite the fact that it cannot be seen, "the circumstantial evidence stacked up". He then quizzed the engineer on what the circumstances were. The answer given was that the tank did not fill up and, after flight there was fuel discovered in the blow-off valve exit and a residual stain on the bomb bay door in the vicinity of that exiit. Now, the staneval eng didn't claim to be Perry Mason, but that has to be sufficient evidence that the blow-off valve did operate during that flight and, therefore, it remained a possibility that it could have operated on 2 Sep. The Coroner stated, in his summing up that, because no-one can see a blow off, he has to disregard it as a possibility.

Incidentally, I do agree with him that there is no evidence that fuel from the blow off valve flowed into the 7 tank dry bay. However, it clearly has to remain as a possible source of fuel for the probable cause of the fire.

He didn't really establish where and how the hot SCP pipe elbow fitted into the 7 tank dry bay. He said that only the crossfeed pipe is in the 7 tank dry bay and that the crossfeed pipe is too high up in that bay for the nearby fuel pipes to supply fuel onto it. The fact is that the SCP pipe elbow is inside a fairing that forms part of the rear portion of the dry bay floor panel. All fluid in that bay will fall onto that panel and, due to air flow (its not a sealed panel), flow rearwards onto the SCP elbow. He didn't accept some very logical thinking by the BOI.

He said that a fuel feed pipe (supplying a stbd engine at 25 psi) was probably the source of fuel for a sustainable fire. He didn't ask any of the experts present how that fuel was going to maintain its flow rate past the front spar (solid metal cast) and then the rear spar (solid as well). I can accept that an engine might run normally with a large fuel leak in its feed lines. The refuel pipes in the dry bay, within feet of the hot pipes were pressurized up to 50 psi for 6 mins with some spiking above that shortly before the fire became apparent. You don't have to be Perry Mason to work out where the fuel probably came from.

Broadly speaking, his summing up, despite thanks to the BOI, was IMHO an insult to their diligence and integrity in discovering serious failings in the airworthiness process.

I cannot say how I know this stuff, but it is all true.

I'll certainly get back to you about the October report. On the face of it, as JFZ90 has also noted, there appears to be a significant change in the conclusions on the same piece of work. We are closing in on the crux of the matter...

Ed

[EdSett100]

DV:

I know that the "tea stain" track was overlooked by the BOI along with the non-activation of the temp probe in No. 7 tank dry bay area. Waht else do you need to know.

The tea stain track was indeed overlooked by the BOI because it was, indeed, a tea stain. We have a galley sink drain in the vicinity of the Stbd 7 tank dry bay. This caused some much needed laughter in the room.

I disagree that the temp probe was overlooked. I assume you are discussing an overheat detector. It is set to operate a red light immediately below the flight refuelling switches on the flight deck. The air engineer was one of the most experienced and capable individuals we had. It is standard practice to make a clear announcement on intercom if that red light illuminates. He was operating the refuel system and that light was directly in front of his eyes. He didn't mention it, so it didn't illuminate. What does this tell us? It tells us that there was not a significant hot gas leak in the stbd 7 tank dry bay. The detectors are cleverly placed to protect other systems (it is possible that these detectors were mistakenly thought to be the fire detection and suppression system quoted in the safety case; but I speculate). It is possible that a small leak played directly onto a fuel pipe coupling and caused the seal to fail. For that reason, the BOI correctly identified that scenario as one of the possible causes of the fire.

Regards
Ed

[EdSett100]

Tuc:

You can’t say the risks don’t exist – you identified them. The probability of occurrence may be incredible (e.g. caused by “massive electrical failure”) but as the outcome would be catastrophic that results in a Class C risk – Tolerable if ALARP.

Tuc, IMHO, that is not a single point failure. Surely, we must only consider single failures in risk analysis, otherwise a whole stack of "what ifs" will combine to stop us flying. An example of this concept might be this: we must accept the possibility of an engine failing in flight, so we have engine failure drills and we go flying. However, if we consider that the engine will not only fail, but explode as well and send shrapnel into an adjacent fuel tank which will then catch fire, which we cannot extinguish, such that the aircraft will crash, we might view the aircraft as unsafe. If so we don't fly it. Thats not acceptable risk analysis, surely?

The point I'm trying to make is that a massive electrical fault is one failutre that we guard against with all of our protective devices and drills. We should not formally analyse further any what ifs regarding subesequent failures of the protective devices and further what-ifs, such as a leaking fuel pipe nearby.

We have to draw the line at single point failures. ie. What is the consequence of a failure of one item in a zone with other systems operating normally in that zone? eg, what is the consequence of a fuel coupling failure such that the fuel will leak onto an adjacent hot pipe, that is working at its normal temperature? Thats a valid risk assessment question.

I suggest, for example, that an invalid risk assessment would be:

What is the consequence to the aircraft if a 200V cable terminal on a 3 phase alternator was to corrode to breaking point, creating massive sparks and consequent voltage imbalance which is then not detected within the time that the voltage sensor is rated to activate within, so that the sparks continue for another second or two and ignite a possible simultaneous fuel leak from a nearby fuel pump? IMHO we must not consider these daisy chain scenarios in airworthiness decisions.

Regards
Ed

[tucumseh]

EdSett

The MoD issue Def Stans, but Design Authorities must also issue their own internal Safety Case Policy document, which articulates in detail how they apply the MoD's standards to their products. Extracts from a typical Aircraft DA Safety Pase Policy (in no particular order);



The Safety Assessment shall, in particular, assess the design for vulnerability to;

• Common Cause Failures
• Cascade Failures
• Maintenance Errors
• Flight Crew Errors
• Hidden Faults
• Faults in related systems
• Environmental Effects
• Lightning Effects

Zonal Analysis facilitates assessment of Cascade Failures. (A consecutive sequence of individual failures where each successive failure is a result of the preceding failure).


If a Hazard is considered and discounted, the reason must be recorded. It is not acceptable to expunge it from the list.


Any Safety Case which treats a (sub system) in isolation, and ignores the system or system of systems as a whole, is likely to be rejected (by Boscombe Down).


The environments within which the system functions (must be assessed), particularly defining where is passes from one environment to another (e.g. the passage of a fuel line from a wet environment to a dry one).


Where a Failure Condition resulting from a Functional Failure of a system can be made worse by additional Functional Failures or adverse events, either from within the system under examination or externally from a separate system, then this combination must also be considered.






If you mean MoD itself does not look at such detail, then you are correct as they seldom have the detailed knowledge. But DAs are required to and must demonstrate they have complied. As this particular book says, there is no point in not complying as they would be snagged by Boscombe. Of course, this always assumes MoD has the DA (and now Boscombe) under suitable and continuous contract to maintain the build standard. While mandated in airworthiness regs, the requirement is not complemented with funding.



In short, MoD have rafts of people with, in one hand (a) a letter of Airworthiness delegation warning them of the dire consequences of not complying, and in the other (b) an e-mail from bean counters telling them they can't have the resources to comply with the legal requirement of (a).

[Distant Voice]

EdSett100; As requested, in reply to

All the facts were examined

You said

Oh no they were not. The only facts that were examined, and they were all available, were the ones that the Coroner wanted to examine

Sorry for the misquote in my original posting, but my question to you remains the same, what facts presented to the court were not examined? Let us not forget that whilst the inquest was driven by the Coroner, MoD had its own legal team in court to ensure that all points were covered.

On the question of the "tea stain", you know very well we are not talking about a tea stain from the galley, we are talking about the statement made on oath by a Kinloss tradesman regarding fuel tracking after a possible blow-off.

"It was like a tea pot stain. Starting below the No1 tank blow-off outlet it was about 6-9" deep and below the bomb bay door hinge line. It followed the contour of the fuselage about a foot below the door hinge line before climbing up and crossing the hinge line near the galley drain"

This statement, along with the airflow diagrams presented by BAE Systems, were a clear indication that, even if a blow-off had taken place (and no one had ever seen one), the fuel would track below No 7 tank dry bay area and the SCP elbow. That is to say, that is most unlikely that fuel source came from the No.1 blow-off outlet.

Anyway, I believe that the bottom line is that the Coroner declared the current Nimrod fleet as not being airworthy, on the evidence presented to him by Group Capt HIckman and QinetiQ. Both said that the Nimrod system is not ALARP.

Sorry I can not send you a copy of the QinetiQ report, because I do not have an electronic version. The document is made up of 185 pages.

DV

[buoy15]

Mile
Good post - well said!!