Chinook - Still Hitting Back 3 (Merged)

[tucumseh]

One has to remember the GPS / SuperTANS combination presented error codes that were “meaningless”. That is, if the system displayed a faulty the crew had no way of knowing what to do or what it meant, so would in all probability have to ignore the system or switch it off. The resultant distraction is self evident.

The GPS unit had a number of faults. Time of Day output was faulty, as was the power supply; both fairly fundamental issues in a GPS system.

Neither the GPS nor SuperTANS was cleared for use.

The SuperTANS installation was vulnerable to EMC problems.

Despite the above, MoD’s position remains that both systems were perfectly serviceable. Despite warning crews not to rely solely on the systems, MoD’s case relies solely on them.

I can’t reconcile these facts. Too many problems to be absolutely certain the system was working correctly and displaying the correct information.

[walter kennedy]

Tuc
The problem of concern with the SuperTANS at the time was not interference, etc but fundamental accuracy.
Robin C
CPLS gave very accurate range but was limited to about +/_ 4 degrees in bearing - good enough to home in on someone you wanted to pick up.
There's plenty of info on it - just got to read, understand, and not go off half cock.
Were you on about a co-located VOR/DME?, they're a bit better for you to try.

[tucumseh]

The problem of concern with the SuperTANS at the time was not interference, etc but fundamental accuracy

Walter, I think you should read the whole post.

EMI was an acknowledged problem.

What would cause your fundamental inaccuracy? SuperTANS is a simple rubbish in, rubbish out calculator. Inaccuracies could be caused by sensor input error, failure, signal interrupt or data corruption; such as having a faulty GPS, which I mentioned and MoD admitted (and yet continue to deny!).

Also, the SuperTANS may be receiving accurate information, but if the display is faulty or damaged (or, as in the Chinook, very difficult to see in bright light), then the information is useless as it is not presented to the crew.

You post as if I am completely wrong, but in fact we are in total accord on this point.

[dalek]

Supertans

Off on my Christmas Hols to Costa Rica tomorrow. A little Marlin fishing to catch up on.
John Purdey and Cazatou,
Don't you find it ironic that the Day evidence to the HOL, which I watched on the Parliament Channel, relies entirely on RACAL STANS analysis?
Equipment which the crew were told not to rely on.
Was it lies, ineptitude or just very poor briefing by his staff?
A very Merry Christmas to you all. Back New Year

[walter kennedy]

Tuc
I believe that Flt Lt T's concerns were about the positional accuracy - your other points may have compounded this.
Further, the STANS CDU was indeed hard to see - but all the mavigator had to do was feed it to the HP's horizontal situation indicator (HoSI).
Now this may be news to many of you, but as far as I have seen, that the STANS was most commonly used via the main navigation display (the HoSI) didn't get a mention at any of the inquiries.
There was some little reference to the "steer meter" - calculating bank and displaying on the AI - but nothing about range & bearing on the main one!!
Nor did any of the pilots who visit this forum mention it.
How can this be? It's not a secret in civil aviation or in US military documentation.
No wonder debate never got as far as how GPS and Doppler data together generate bearing, range, and track by the time the data for a waypoint gets to the HoSI.

BOAC
Part has been sent (a while ago) and the rest will follow this week - just have to wait now won't we?

[chinook240]

that the STANS was most commonly used via the main navigation display (the HoSI) didn't get a mention at any of the inquiries

I would imagine the reason it hasn't been mentioned is because the RNS252 did not have any connection or input into the Horizontal Situation Indicator (HSI).

[walter kennedy]

240
Thank you
that explains a lot
If we had had clear info like this years ago it would have saved so much time being wasted.

[walter kennedy]

240 committed himself to an opinion on the avionics of interest which should have triggered off interesting and informative exchange of ideas such that a common understanding of the navigation systems could be reached - what should have been a starting point years ago.
Gentlemen, the silence is deafening - don't be shy of putting your understanding forward, some systems are hard to grasp and you, as aircrew, needed to use them well, not build/fix/tweek them. One of my ex's had a favourite saying when I went into unecessary detail on, say, a car fault - "Tell me the time - not how the clock works!".
Problem is in this case, to understand their options, we do need to understand the nav systems.

[tucumseh]

we do need to understand the nav systems

I dare say the crew thought much the same. Flt Lt Tapper had to resort to visiting Racal to try to work out SuperTANS. (An extraordinary event - the details of which should be available in both Racal and MoD files). He probably found it disconcerting to be told the Error messages were “meaningless” and that there was no longer any indication of how accurate GPS was – yet the same system in the Mk1 was apparently still ok. He probably wanted to know what changes had been made during Mk2 conversion, as no-one in MoD had bothered telling him. Given that single simple fact, under MoD’s own rules the aircraft should not have been released to service. That is why any inquiry should always start with this question to ACAS – “Why?”.

[walter kennedy]

<... that there was no longer any indication of how accurate GPS was ...>>
I believe that was only the case when the Doppler system was not functioning (and I mean not functioning/working as opposed to not being selected) - as I believe, even with GPS mode selected, the system continually compared the GPS position with the Doppler position and flagged it up if the discrepancy was beyond a certain amount (makes sense, don't it?).
Even with GPS mode selected, I believe that for generating steering guidance the system still took several parameters from the Doppler side of the STANS - I'm travelling just now and so can't getback to my usual computer to dig out the stuff so this from memory just now - perhaps this input is not known about by those who use the system to navigate - even if you are in GPS mode (as is my understanding) and have STANS (or what ever the nomenclature is on the button - DGPS/TACNAV - I haven't seen an HC2 HoSI mode select panel close up) selected on your HoSI there is an influence from the Doppler system in what gets to the HoSI.
Don't forget, the GPS of the time, apart from the odd glitch and low update frequency (once a sec?), was lagging about 2 seconds.
I hope 240 was not trying to say that STANS as a whole was not selectable to feed the HoSI! - if that were the case, I'd have to agree with one of the popular mantras "the cause of this crash will never be known" - how the HC2 was navigated would never be known!!!
How about talking this aspect through? - getting that overall systems understanding?
Please Tuc et al, don't deflect straight away with airworthiness and interference etc - there is clear need to focus on the basic nav just now - or no one will be able to follow the arguments.

[tucumseh]

Walter, not for the first time you launch into a reply without ascertaining facts or reading source documents.

From the Release to Service, extant at time of crash;

Para 2.2 "GPS has not yet been declared operational by the US DoD and accuracy is therefore not guaranteed to any level. Even when GPS is declared operational by the US, accuracy of TNL8000 GPS (the system fitted to Mk2) could degrade substantially without any indications to the crew".

Para 2.3 (a) "In addition to para 2.2 above, the GPS is highly susceptible to jamming of which the only indication is loss of GPS..... The "ERR" figure displayed, which has conventionally been taken as a measure of GPS performance, is meaningless and so no indication of the accuracy of the GPS is available to the user".

There is no equivalent statement in the Mk1 RTS. The only reasonable assumption aircrew could make from this fact is that something had changed in the Mk2 that did not affect Mk1. As they were expected to operate a dual Mk1/Mk2 fleet, it was incumbent upon MoD to eliminate this uncertainty by finding out why there was a difference, agree what action to take and advise aircrew accordingly.


They didn't. They simply inserted a ludicrous statement that the "ERR" message was "meaningless". To me, that is a potential distraction, human factors risk, call it what you will. As I have said before, it must mean something, even if it is that the installation design is crap.


As you say;

there is clear need to focus on the basic nav just now

To me, it is a pretty basic failing if the system MoD's argument relies upon is "not guaranteed to any level". A logical extension of that argument is that Wratten and Days conclusions cannot be sustained to any level.

[chinook240]

I hope 240 was not trying to say that STANS as a whole was not selectable to feed the HoSI

Err, yes, I am.

how the HC2 was navigated would never be known!!!

I hate to say it, but the same way we do today, and when the ac was introduced in 81. Hope that isn't too scary for everyone.

[BOAC]

I hate to say it, but the same way we do today, and when the ac was introduced in 81. Hope that isn't too scary for everyone.

- yes, why some think you need an 'HoSI' to 'navigate' at low level I do not know.

[tucumseh]

With apologies to Boscombe and MoD(PE), when I said it was incumbent upon MoD to resolve the uncertainties I mentioned, I should of course have said “RAF”. It was they who said the aircraft should fly, not the other two. Boscombe were trying to resolve matters. They were awaiting necessary information from MoD(PE).

Walter, if you want to focus on the basic Nav, may I suggest you start with a list of what Navigation equipments you mean. In fact, three distinctly different lists;

1.What MoD say was fitted
2.What we know was fitted
3.What you think was fitted

(They get progressively longer).

Then ask a basic question. Of the equipments listed, which were cleared for use during flight?

None.

Analyse that.

[Chugalug2]

Walter, I have no knowledge or experience of the Chinook of whatever mark or of its nav kit, but I think that you are suffering from a fundamental misconception about military tactical flying, be it rotary or fixed wing. So far you have encouraged us to believe that these pilots slavishly followed the DME from the wacky radio counting down until it counted them down into a hillside. Now you propose that they slavishly followed an HSI, whatever it could or could not be coupled to. As others have repeatedly pointed out the navigation of such low level sorties was, and I suspect still is, Mk1 eyeball, map, and pilot navigation (1 in 60 rule etc).
The Hercules K model was stuffed full of avionics, mostly UK made to the extent that half the aircraft's initial cost was in pounds Sterling. We had Decca map displays that purportedly told you where you were on a badly distorted roller map, providing of course you first told it where it was beforehand and were in the area of coverage. We had doppler roller map displays that consumed a fortune in charts as the Co-pilots had first to perform Origami on them and discard the excess. With the inherent drift involved it was very much advisory only in its authority.
In short you were/are responsible for knowing where you are and what is ahead, not the bloke wandering around the Mull with a backpack, not the shysters who flog dodgy kit to the MOD, not even the MOD for buying it, you are! I do not share the theory that this accident was nav based, illustrious though its proponents may be. This aircraft was a death trap, that was set when it was granted an RTS into RAF service, and was very likely sprung seconds before it killed 29 people.

[vecvechookattack]

All this gumpf regarding Supertans and GPS is a massive rabbit hole you are all disappearing down. They had a map....they were trained in navigation....they were not relying solely on GPS to navigate ...so why were they lost, in cloud and below the safety altitude? Poor airmanship - thats why.

[tucumseh]

Vec

Even if your last statement were true, your post acknowledges the possibility of these uncleared nav kits being inaccurate/faulty/defective etc.

MoD's case is built on them being fully serviceable (they were not) and able to be used in the final moments (one was switched off).

That rather proves the point of those whose sole aim is overturn the verdict. There may have been poor airmanship. That there was prior negligence does not make you wrong. The difference is that this prior negligence is demonstrable fact.

[vecvechookattack]

I totally agree with you. I have said all along that these aviators were not grossly negligent. They displayed poor airmanship, poor captaincy and were unprofessional. But they were not grossly negligent.

[Chugalug2]

tuc:

There may have been poor airmanship.

vecvec:

They displayed poor airmanship, poor captaincy and were unprofessional.

Spot the difference?

[Bertie Thruster]

I can't see any evidence to suggest:

They displayed poor airmanship, poor captaincy and were unprofessional

low flying with passengers.

?

they didn't plan the sortie sufficiently, the brief was poor, the plan was bad, the nav route was poor, they should have turned around

??

Are you joking?