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Mick - some possible explanations to your question:
You say the SI was clearly relevant - why was it? As it related to the FADEC which others had erroneously suggested was the definate cause!
To paraphrase "why would they say it flies like a Mk1?" - you could argue a Mk2 with a failed FADEC where you have to shut down the engine flies exactly like a Mk1 which has also had an engine failure. Engines do fail - aircraft must be able to be safe in such circumstances which are not rare.
I've no idea why it was not mentioned in the BoI, but perhaps for the reasons above it was not considered relevant? Who thought it shouldn't be mentioned? Is there any proof of that?
The main thing is - is it relevant? Doesn't seem like it had any bearing on the accident to me, but lots of readers of the times might now think so!
You ask why so many were certain the pilots were to blame? I'd suggest this is related to the balance of probabilities as to what happened - as discussed here this is quite a different to proof "beyond all doubt". I will go no further as it is not good form and the thread will get locked.
JFZ
"PS do droop stops still fall out or is that now fixed or just prevented by "inspection"? "
Speaking as one who learned that Fixed Drop Stops were "not square" at the same time as everyone else at ODI, this particular check was made on all subsequent Rotor Head builds since then - I seem to remember the Section bengo even wanted to get in on the Indies! (But we told him he'd have to attend at 2 in the morning to meet deadlines)
Initially this was NOT a part of the US/UK Rotor Head Overhaul manuals, but was subsequently amended in the very late 80's (for Mk1). As the heads are no different to the new Mk2's I assume the same warnings/instructions exist.
I don't know if this check made it to Mk 2 Base/Line maintenance manuals? But I haven't heard of too many (UK) ones dropping off lately.
There is a thread about this very subject here on PPRuNe - possibly in the Rotor Heads forum.
Last edited by Rigga; 8th Jan 2012 at 19:36.
Reason: Thread line
This implies that whilst the control becomes very limited if a FADEC fails, and the affected engine should be shut down for landing, it is not in itself necessarily a catastrophic hazard.
AFAIK this FADEC design was unique in that if it failed there was no manual reversion. It was also very prone to failure in that, as tuc has reminded us, an audit of its code was abandoned as the amount of mal-coding was too large to complete economically. It could not even be relied on to go into reversionary mode following failure, as the number of uncommanded power ups, downs, and shutdowns testify. It was, in short, so bad that Boscombe Down pleaded that the RAF ground the Mk2 (which was already in squadron service thanks to the creative use of the RTS system). I don't know what your motivation is to try to characterise the FADEC/DECU problems as a storm in a teacup, but for my money it was Gross Negligence by the MOD that this aircraft entered RAF Service in this state, let alone to be tasked for VVIP transport over the express protests of the Detachment Commander.
AFAIK this FADEC design was unique in that if it failed there was no manual reversion. It was also very prone to failure in that, as tuc has reminded us, an audit of its code was abandoned as the amount of mal-coding was too large to complete economically. It could not even be relied on to go into reversionary mode following failure, as the number of uncommanded power ups, downs, and shutdowns testify. It was, in short, so bad that Boscombe Down pleaded that the RAF ground the Mk2 (which was already in squadron service thanks to the creative use of the RTS system). I don't know what your motivation is to try to characterise the FADEC/DECU problems as a storm in a teacup, but for my money it was Gross Negligence by the MOD that this aircraft entered RAF Service in this state, let alone tasked for VVIP transport, and that over the expressed protests of the Detachment Commander.
I don't think I am trying to say its a storm in a teacup - its early history was woeful. I think the issue is the blurring of what was safe when, and how bad things really were and what was exaggerated after the event.
What blurring? I don't know if you followed the Mull thread (now locked off but still accessible). Other than one somewhat idiosyncratic member, no-one other that the MOD apologists said they knew why the tragedy happened. No CVR, no ADR, no survivors, no eyewitnesses of the aircraft immediately prior to impact, no definitive evidence from the wreckage. The only burring was done by the AOC and the AOC-in-C, the RO's. It took 16 years for that "blurring" to be undone. What is not blurred is the illegal RTS, and the Gross Unairworthiness of the type when it was issued. I don't see how that can be exaggerated, whether the RAF wishes to confront it or not.
I understand that SI/Chinook/57 is in two parts; initial application and subsequent inspection. The initial application requires the marking of "witness lines" across the connectors and the receptacales on the DECU box. Subsequent inspections call for a check for movement by reference to the witness lines.
Question 1. When a DECU box is replaced it is most unlikely that the witness lines on the receptacles of the new box will line up with those on the aircraft connectors. Do we clean everything off and start again with "initial application"?
Questuion 2. When subsequent inspections are carried out in-flight (every 15 mins), who signs for them, and where are they recordered? Perhaps the Chinook as the sort of sign up sheet we see for public toilet cleaning. "This connector was checked at ______ hrs, by ______. Next inspection due at _____"
Question 1. When a DECU box is replaced it is most unlikely that the witness lines on the receptacles of the new box will line up with those on the aircraft connectors. Do we clean everything off and start again with "initial application"?
Logically a new DECU box* would be unmarked so one would only need to tighten the connector and place a witness mark where the connectors mark is...
*One is assuming you don't replace an old DECU box with another "used" one...
It appears, from close up photographs of a DECU box, that the connectors used are of the Amphenol Threaded type; hence the working loose. If this is the case, then they should have been replaced by a Amphenol Bayonet type connectors. But that involves time and money, and if you are in a hurry you have neither.
I believe that the connector pins used are of the EMI/EMP type. So clearly the DECU is very susceptible to EMI, RFI and EMP. Having a loose connector would not help the situation.
It also appears the the main connector to the Hydromechanical Metering Unit (part of FADEC) is of the Amphenol Threaded type. Of course that can not be checked in flight.
DV
Last edited by Distant Voice; 9th Jan 2012 at 12:22.
"The Sqn Ldr emphasised the frequency and volume of these types of failures both before and after the crash of ZD576. Because they were not well understood by either aircrew or ground crew, and there was then little guidance from the manufacturer, the standard fix for these problems was first to swap the two engine DECUs and if the fault re-occurred to then change the DECU. If the problem continued ground crew would change the Hydromechanical Actuator. The squadron had to change the DECUs so often that they ran out of them. A further problem in understanding and rectifying faults during this period was that the type of faults normally left no trace and were very difficult to replicate on the ground and therefore verify and diagnose. The reverse of this was also true in that some ground checks did not function properly. For example, the overspeed ground check often produced the very fault it was intended to avoid.
The poor serviceability of the aircraft also had a knock on effect on fault reporting. A tendency developed unofficially amongst crews but which was strongly supported by squadron executives to not formally report all faults because squadrons stood to lose one of their few, or their only, remaining serviceable aircraft and thus be unable to fly and meet tasks. As a result the Sqn Ldr considered that formal fault records that the Department have presented to demonstrate the relative good serviceability of the Mk2 as it entered service would significantly understate the true position."
What the witness did not know (I've spoken to him) was that funding had been slashed for Fault Reporting by the RAF Chief Engineer. (CHART confirms a 25% overall cut in 1992; it was actually 28%, 3 years running). EAs were instructed not to submit requests for investigations, but save them up and submit omnibus requests. This became academic as (a) junior suppliers were permitted to over-rule senior engineers within AMSO/AML and prevent requests being approved, and (b) funding was chopped to the extent even safety related investigations were refused.
When you put both these issues together (Sqns and EAs not reporting and funding being stopped), it places the criticism of the aircrew and ground crew (for not reporting faults) in a completely different light. The Chief Engineer would have known of this, and certainly his 2 i/c did (Director General Support Management, an Air Vice Marshal) because the latter threatened his staffs with dismissal in December 1992 for drawing attention to the gross, systemic failures being encouraged and perpetrated in the Chief Engineer's name. This, during the so-called "Golden" age of airworthiness.
I would very much hope that this SI on the DECU connectors was removed many years ago following corrective action to address the cause, or at least some palliative action in service (e.g. application of wire locking) to negate the need for in flight checks.
Can anyone confirm that?
It's the basics here - in my view you just don't carry out in flight checks of anything unless the aircraft is signed up for a Check Test Flight, or a specifically documented In Flight Check. For an engine control connector, this would normally be a 'one off' to investigate a problem. In any case, you are checking for something that you really can't tolerate happening - it's got to be fixed, not checked.
If (and I really hope that I'm wrong here) this SI is still in use, then there is something seriously wrong in the State of Denmark here. It's a threaded electrical connector - it must have been fixed by now. If not, the RAF have some explaining to do.
Best regards as ever to those actually trying to do the job at the front line
If it was threaded, that would perhaps explain why 15mins may have mitigated the hazard (easy to spot, early indication of onset, probably take a while & several turns to fully loosen).
Thats not to say its acceptable and should not have been fixed ASAP - just that the mitigation, however undesirable, was probably effective. If the check was conducted of course - but the crews were probably keen to ensure the connectors stayed connected.
As you say engines, I'm surprised some form of interim wire locking solution could not have been developed.
DV
Quote:
I believe that the connector pins used are of the EMI/EMP type. So clearly the DECU is very susceptible to EMI, RFI and EMP.
Is your conclusion that the DECU is susceptible based on the type of connectors used? Designing to avoid EMC problems in an aircraft environment (e.g. through connector choice) is common practice - it doesn't necessarily indicate that there is a known weakness or history of problems with a specific equipment.
I'm not a helicopter man, as you know, but it seems to me that a crew flying over badlands in a shooting war, all busy performing their roles, might have better things to think about than checking a simple, but critical connector every time the egg timer goes off.
"Sorry, Captain, I've go to stop looking after the machine gun and the casualties while I go and check the MoD's mistake to make it's not going to kill us."
Don't even bother telling me who does what or even if they have a mchine gun. You know the point I'm trying to make!
Absolutely spot on. Crews on ops simply can't be required to check that bits of their aircraft are still attached. Crews on training shouldn't be doing that. Crews on SAR shouldn't be doing it. Crews just flying around on GFP shouldn't be doing it. No one should be doing it. At all. Ever. It's not their flaming job. It's the engineers, and until it's fixed, the aircraft stays on the ground.
JF, the point is not that 'it's threaded, so 15 minutes mitigates'. 'Easy to spot' is not the point. 'Several turns to fully loosen' is definitely NOT the point. The point is that no aircraft should ever be allowed to get into the air with an electrical connector that affects the integrity of the engine controls not properly secured so that it might come loose. Especially, especially, if you know about it.
It's not rocket science, honestly. It's stopping a plug falling off, and we've been doing this for years. This is basic aircraft engineering standards and practices. Our crews deserve far better than this, and if people are still signing this one off they need retraining until they stop doing it.
I hope I'm not coming over as too judgemental here, but honestly, the fact that we might still have some people who are prepared to tolerate this sort of thing sacres the bejeesus out of me....
If it was threaded, that would perhaps explain why 15mins may have mitigated the hazard (easy to spot, early indication of onset, probably take a while & several turns to fully loosen).
I do not know your background, but the only way to mitigate this hazard is not to fly. The only way that Nimrod's AAR hazard was minitgated was to avoid AAR. It took a long time to sink in with the RAF Chiefs, but that was the final solution.
The DECU is shown as having a threaded connector. Why did the BOI not go down this road, and why does it take a "retiredee" to discover it 17 years later?
DV
Last edited by Distant Voice; 9th Jan 2012 at 20:05.
I would very much hope that this SI on the DECU connectors was removed many years ago following corrective action to address the cause, or at least some palliative action in service (e.g. application of wire locking) to negate the need for in flight checks.
MoD's answer is that "this SI was withdrawn from use in 1995 and the details incorporated into he normal Chinook Maintenance Manual". So it looks as though the connectors remained and the SI just became part of normal servicing.
"MoD's answer is that "this SI was withdrawn from use in 1995 and the details incorporated into he normal Chinook Maintenance Manual". So it looks as though the connectors remained and the SI just became part of normal servicing."
'Withdrawn' may be for any one of several restorative reasons, including a possible modification action, the details of which would be placed in the AMM.
Please keep this thread's discussion to 'speculation' and try to avoid 'wild' speculation.
Also: Engine's missive that "Engineers should do it" implies blame on the shop floor when in reality they can only react (legally) to "Servicing Instructions" from design engineers/PT staff.
"MoD's answer is that "this SI was withdrawn from use in 1995 and the details incorporated into he normal Chinook Maintenance Manual". So it looks as though the connectors remained and the SI just became part of normal servicing."
Photgarphs in a 2006 trainee handout show DECU THREADED connectors.
Threaded they may be - but are they sealed and/or locked?
There are many ways of locking joints, even mere threaded Plugs and Sockets. I'm afraid you'll have to do better than quoting a photgarph from "Training Notes in 2006".
I assume from your location that you are amongst Bristols 'finest'. If so, find someone who can back up your proposition rather than wildly speculate on some unpublished picture from more than 5 years ago.
I have a picture of Fairies at the bottom of my garden...
To take a point made earlier that SIs were issued by MoD(PE), and as DV seems to have the actual Servicing Instruction, could he confirm who issued it? If PE haven't signed it, then what indication is there that it has been validated and verified? I did a tour in that PE department and from the info on this thread I'm fairly certain it would have been thrown back and a formal modification required.
The other point about Odiham apparently amending the SI to an in-flight SI is, as Engine says, not a recognisable procedure. You've got to wonder at what was going on higher up in the RAF if Odiham felt it necessary to resort to this.
With apologies to Tuc and Pulse1 who discussed this a long time ago on the ZD576 thread. The rest of us catch up eventually.
