Thanks I.I. all perfectly easy to provide that
 

I didn't think most of those points were in dispute.
Most of them acknowledged by Nick Lappos and JimL on this forum.

If you can't see what the downsides of the twin are then you don't have a balanced view - the upsides are obvious: it is possible to continue flight when ONE engine fails.

Engine failure rates need to justify the Gearbox/Freewheel/Tailboom deaths - maybe they do? Particularly with larger helicopters - perhaps.

BUT it is clear that the evidence of accident rates to twins are not inline with the maths which is used to justify that approach - 10^-9 !?

Now don’t go throwing your toys out. I was just struggling with that consonant in AnFI or I might have said Freakin’ Idiot or Ferkin Idiot (but accepted, this also would be quite rude).

It’s Christmas and in that spirit I retract those names and am opting for something more seasonal/biblical. What about Holy Pontificator?

Happy Christmas TT

and agree this thread shouldn't be about twin/single - but it's too much to sit back and hear the complexity of the fuel system and see how many don't undersatnd it yet and FAIL to make the hypothetical link to this FATAL and DISASTEROUS ACCIDENT....

... do I really need to PROVE that a twin delivers power to ONE common rotor system? are we in denial?

Lol

Truly, Holy Pontificator, your really are a corker. Season"s best.

TT

FDR or CVR
 

Unless an aircraft is already wired up with the required sensors and possible instruments it would be quite a task to install a FDR but not impossible. However, a CVR or a Video Camera trained on the Instrument panel would suffice for an interim period. Back in the day, and I have been retired too long to know about modern technology, the CVR's on BHL aircraft had four channels one of which read the Rotor RPM, which might have been useful in the pub accident investigation.

As there's no real link between Glasgow and a fuel issue ...
 

While out on a cobweb busting bike ride, I realised, having recently completed an OPC, that the problem with a double engine failure in a twin is that you only expect it to be a single engine failure and don't immediately lower the collective! I would guess that by the time it takes to realise both engines have gone, the rrpm has dramatically reduced.

However, that doesn't explain why they both might have failed at the same time.

Art of flight,

Post 1502 explains why I think fuel maybe the issue. It was a post by Robin 400 some time ago and a look at the 135 fuel schematic that got me thinking.
The only fuel to come out of the supply tanks into the main tank is via the spill Chanel's at the top of the rear fence ( in normal attitudes of course).
Despite all speculation the facts to date seem to indicate both engines and drive train were serviceable but stopped. Only two possible reasons, both engines have been shut down or no fuel getting to them.
A faulty non return valve would go undetected until a particular set of circumstances came about. Low fuel in main tank, pitch up or down, and one transfer pump off. This scenario would not illuminate a transfer pump warning as it is still pumping fuel It's just not reaching the supply tanks. I accept that the supply tank low level warnings and gong should still be working, but his main tank gauges are showing fuel and his transfer pump is working. (Confusion) My point is a faulty NRV will only reveal itself when fuel is low, one transfer pump is off and the aircraft is pitched forward or aft. What is really crucial here is where did the AIB drain the 95ltrs of fuel from? Main tank or supply tanks?

Issued 19 December by Eurocopter :

The second ASB (EC135-28A-019) introduces a revision of the flight manual with regards to the low fuel warning and the fuel pump caution indications. The corresponding airworthiness directive to be issued by EASA will be an Emergency Airworthiness Directive, meaning the revision to the manual must be made immediately. This is not because there is a safety concern. Rather, the emergency directive ensures the revision is made immediately instead of at the next scheduled update of the manual.


Issued 23 December by Eurocopter :

Following the Alert Service Bulletin released on December 19, one-time checks on the fuel tank system of the worldwide EC135 fleet continue. As of today, 264 sensors have been tested. Of these, 12 needed to be cleaned but were fully functional afterwards, while two failed and needed to be replaced.

Eurocopter continues to monitor the checks closely and will provide updates as more information becomes available.

Modern EFIS aircraft with everything on a digital data bus should be much easier than in times of old. Yes you still need a DFDAU to package all the data together into the right format/frame rate, but such things as air data, attitude and heading, control positions, engine and system parameters will most likely already exist in digital format so probably no additional sensors required, and the above data will probably already be on just a few ARINC429 busses, even if not already concentrated onto 1 general purpose bus to eg feed the screens.

So on the 135, are you saying that an engine can fail to the extent that it becomes a net torque drag, without a command input, without a clear cockpit alarm? Strikes me as a bit of an oversight.

AnFI

I don't know if you fly, or what you fly. But of you do fly and you like single engine over and above twins, because you feel that twins are too complex, then carry on as normal. I hope you are not ambitious, because your paycheck will always reflect the size and complexity of the aircraft you fly.

From my experience:

AS350B2 and AS355F2 in Australia - no difference in auto but did not do touchdown in 355F2.

I would need to research the interior of the 355 versus the 350 MGB. The 355 has a CBOX (a horrible thing) which would probably limit the twin SHP take off power. If the MGB has more stress, the certification calculations will have been done and it it will have a lower overhaul life.

Complicated fuel systems - if you can't work a fuel system, you shouldn't be in command of an aircraft. Most systems need little work but at most its moving a switch once in a while to balance fuel.

Confused pilots - can happen in any aircraft, would you want all jets to be single engine as well?

Thanks for the entertainment, but I am getting bored with the discussion now and I won't bother arguing with you anymore.

Police helicopter crashes onto Glasgow pub
 

Twins are inevitably more complex than singles and that in itself can be regarded as making them inherently more dangerous- only because there is a greater chance of a systems failure or pilot error. For this reason more attention is applied by designers to mitigate the risks and to ensure that the advantage of two engines is not outweighed by the disadvantages. In a single you have no choice if your motor goes, a twin will stay airborne to get you back to base or extend the choice of Landing site beyond a simple cone. If both donkeys go, then you are no worse off than flying a single.
Single engine overflight of built up areas is prohibited for this reason which is why commercial, police, air ambulance all use twins. They don't have a choice- correct? Complexity is addressed by training and type conversion and in itself it isn't a threat.

Could you explain this in normal language please?

His way of saying a low rotor warning system perhaps....:confused:

From Eurocopter:
What is the testing procedure?
Did the 12 sensors referred to above also initially fail?
If so were they in situ or on the test bench?

Mickjoebill

...ground run and waiting for LOW FUEL WARNING LIGHT comes ON...and checking the accuracy...

JR

Main purpose of the test is the correct illumination of the yellow FUEL caution ( before the red FUEL LOW warning ) and the indication of the correct fuellevel in the supplytanks. Thats what the sensors are for.


skadi

Mickjoebill, Very good point. Eurocopter also fail to mention if any of the aircraft concerned had more than one dirty or failed sensors. Potentially there could have been two aircraft, each with all six fuel sensors working incorrectly until after the sensors had been cleaned.

Likewise, by how much did the condition of the cleaned and re-used sensors differ from that of the two that were scrapped?

.

Police helicopter crashes onto Glasgow pub
 

A former army air corps pilot and now colleague was trying to explain rotor droop / mushing to me today. I understand this is effectively a quasi stall where caused by rapid aft cyclic input perhaps while executing a tight turn or pulling out of a dive. I understand this can result in a rapid loss of height with ineffective control. Can anyone enlighten me further as I am not sure if there is any relevance in this case?

We used to do a demonstration to our students on gazelle, called jackstall on the syllabus. It was a dive to high speed with high power and an aggressive manoeuvre was carried out. The feedback forces then exceeded the control authority and control was 'lost' (sort of). Immediate action was to reduce power and severe control input, hey presto, all was well.
The reason for this was to scare them out of trying to wazz the helicopter and how to get out of it if you overloaded everything. Instead of jackstall, it could have been called 'gross mishandling with a single hydraulic system', not as punchy?
Whilst not impossible to occur on ANY hydraulic control helicopter, it takes a lot of mishandling and neglect to occur on the likes of a 135.
There is also what WE call retreating blade stall caused at high power/high speed, this has nothing to do with hydraulics, however the recovery is the same as above. A police fitted 135 has a lot of draggy bits on the outside and once again it would take a big dive to get the speed. If he was going balls out to get back to base, this could be relevant, but an experienced pilot would just reduce power almost without thinking. Once again, whilst possible, it is unlikely to be relevant