Proposed Mandatory Permit Directive – Jet Engine Fuel Systems

Sadly nothing in aviation comes under the term “cost effective”

Many thanks for the explanation.
Here’s hoping that suitable and relatively cost effective solutions can be found.!

Rob

Thanks for the replies. Yes complex indeed, and I hadnt realised that the same components would of been used in RR, DH and Siddeley (as in Armstrong) designed engines.
My question really stemmed from the fact that to the best of my knowledge no specific fuel flow / regulation problems have shown themselves in the Derwent and Goblin engines of Meteors and Vampires operated for many successful years, both in aviation industry and Airshow participants alike – at least not to an extent that any problems have been publicly reported in the same way as the Avon (why would they I suppose one may ask). And my initial reaction was that it was unfair to lump all of these together for attention rather than sticking to the one giving the most cause for concern.

As ever I’m always happy to be educated!

Rob

The problem is, that regardless of who designed the engine, they all went to the same suppliers for fuel control equipment, which is why you will find Lucas or Dowty hardware bolted on there in many cases. The pump that fuels a Gnat is essentially the same as the one fuelling Concorde, only the size differs so they are all full of the same technology and subject to the same problems. To the best of my knowledge many of the pumps are still supported and I know that on the Orph’ at least some of the smaller fuel control modules don’t contain the suspect elastomers but the main fuel control unit does so getting one of those brought back to life would be a real show-stopper. It’s a real shame but a decision that’d very difficult to argue with.

The problem being it’s the rubber type materials used, one wonders if when stripping down some of the types involved if no problems are found will they reverse the decision on those, of course no one has put two and two together yet and realised the same materials will be used the fuel and oil systems in piston engines as well.

Thanks for the replies. Yes complex indeed, and I hadnt realised that the same components would of been used in RR, DH and Siddeley (as in Armstrong) designed engines.
My question really stemmed from the fact that to the best of my knowledge no specific fuel flow / regulation problems have shown themselves in the Derwent and Goblin engines of Meteors and Vampires operated for many successful years, both in aviation industry and Airshow participants alike – at least not to an extent that any problems have been publicly reported in the same way as the Avon (why would they I suppose one may ask). And my initial reaction was that it was unfair to lump all of these together for attention rather than sticking to the one giving the most cause for concern.

As ever I’m always happy to be educated!

Rob

They’re pretty basic systems Robbie and pretty easy to follow through.
As for the difference between aircraft and industrial, bar the likes of no requirement for keeping the weight down that means that stronger heavier cases and blades etc can be used, the marine Olympus being an example where stainless is used throughout to protect against corrosion, also the need for a barometric fuel control unit as it tends not to need to go to any altitude.

As it happens ours was an all or nothing deal. Our fuel system was treated from beginning to end as though it was being returned to flight with no compromises – how would you decide where to compromise? It’s anathema to the aerospace mindset with good reason. We also have a LP boost pump with certificates of release, not that we’d do anything other than put it back where it came from, but it could fly and we were told during its rebuild that its internals were in better condition than many similar pumps that were flying.
The capability certainly exists to keep these things going, though the people with the ingrained expertise are thinning fast due to retirement and redundancy but to go as a commercial customer with your Cold War jet and its fuel system and as to have it brought up to date would be pretty much impossible in today’s climate, I think.

On the subject of inhibiting the system when not in use, we have the proper juice in a bottle for that very purpose and part of the agreement when handing all of this over to the people of Coniston in perpetuity is that we have to wheel her out once a year to run up the engine, hydraulics, pneumatics, electrics and every other thing that moves. I know it’s not possible to run the perfect project but we’re trying hard.

Thanks for the enlightening and informative answer Bill.

I think that everyone is panicking to early, Yes there is a draft MPD that has come out and if everyone reads it you will see that it is open to discussion for companies to come back with what can be done to prevent the engines from failing. If you think back a number of years, a similar thing happened on the Avon engine that was going to finish the Hunter but the companies operating the aircraft came up with a solution in MPD 2001-001 which allowed the Avon to carry on. That was more serious than this present draft as it involved the actual core of the engine. This draft is to do with the fuel system that is an accessory and can be changed on the engine. I think that everyone should stop slating the CAA over this. At the moment as they are giving the operators of these engines a chance to come up with a solution to keep the aircraft flying and i for one am very confident that this is going to happen. I have been with a CAA surveyor for the last two days and i can assure you that they are willing to listen to solutions. As for St Athan we have diversed into other areas of aviation because we saw the decline in airshows a few years ago but we will still do our utmost to keep a selection of ex military jets flying and working with other companies who feel the same that the day of the Hunter, Jet Provost Gnat etc is far from over.

NAD, you will see that not a single poster has ‘slated the CAA’, in fact quite the opposite, why would anyone do that? The proposed MPD makes total sense since it simply proposes no more than the SOP’s for these engines stipulated in the relevant OEM AP’s. I’m not saying it is right or wrong, but those are the facts from the MPD draft. Also of note is that no one has panicked, but simply stated quite correctly that IF the proposed draft MPD is rubber stamped as is for engines past 20 years since overhaul (and they are out there), it WILL create a great deal of casualties, that much is certain.

We both know that a great many of these engines in flying airframes have not been and don’t go through the anti det’s and inhibiting according to the letter of the book since last overhaul or retirement. I have witnessed this at several organisations. I’m not suggesting that such airframes are not maintained correctly by the way, just realistically stating that we know that airframes sometimes sit for months without engine FCU’s being re-inhibited with the relevant OM fluids, or anti det runs for various and more than often, valid reasons. Has every one of your Hunters and relevant engine types been anti det as per the Rolls book and similarly inhibited when it fell even slightly outside of the OEM schedules instructions in the AP during off season??? Obviously a rhetorical question which I don’t expect you to answer , but that is a relevant question based on exactly what the draft MPD proposes.

No doubt MRO’s in conjuction with the GA surveyors and industry will discuss options (And of course CAA surveyors are willing to listen to solutions). Unlike the great many misinformed, those of us with a brain know that the CAA are not mindless mallet wielding autobots, in fact most are aviation enthusiasts too, especially your local surveyors. However, their business is safety after all. Let’s hope a safe compromise can be found, since we know that hardly any of the engines in current flyers qualify if you subject them to exactly what the MPD proposes, especially back dating it to last overhaul or since retirement.

I’ll hold my hands up and say I know diddly squat about jet engine fuel systems, but what I don’t understand is why the large range of engines being included in this proposal? What problems have the Goblin, Ghost, Viper and Derwent had that justifies their inclusion?

Rob

Because the bits that perish (seals, gaskets, diaphragms and glands) are made of the same stuff no matter who designed the engine (in a lot of cases most likely made by the same sub contractor(s)) and have to deal with the same fuels and lubricants.

A couple of examples of typical hydro-mechanical fuel systems of yore. It should give you an idea how intricate the older units are.
With thanks to RR for their illuminating drawings.
[ATTACH=CONFIG]244087[/ATTACH]
[ATTACH=CONFIG]244088[/ATTACH]

I’ll hold my hands up and say I know diddly squat about jet engine fuel systems, but what I don’t understand is why the large range of engines being included in this proposal? What problems have the Goblin, Ghost, Viper and Derwent had that justifies their inclusion?

Rob

I believe Siemens have the technical data for the Avon 200 now, they bought it from RR a few years back. Many telecoms faciilities use a couple of Industrial Avons as instant-start power generators.

Those are ground-based aero derivatives, the fuel and control unit are different.

I think that everyone is panicking to early, Yes there is a draft MPD that has come out and if everyone reads it you will see that it is open to discussion for companies to come back with what can be done to prevent the engines from failing. If you think back a number of years, a similar thing happened on the Avon engine that was going to finish the Hunter but the companies operating the aircraft came up with a solution in MPD 2001-001 which allowed the Avon to carry on. That was more serious than this present draft as it involved the actual core of the engine. This draft is to do with the fuel system that is an accessory and can be changed on the engine. I think that everyone should stop slating the CAA over this. At the moment as they are giving the operators of these engines a chance to come up with a solution to keep the aircraft flying and i for one am very confident that this is going to happen. I have been with a CAA surveyor for the last two days and i can assure you that they are willing to listen to solutions. As for St Athan we have diversed into other areas of aviation because we saw the decline in airshows a few years ago but we will still do our utmost to keep a selection of ex military jets flying and working with other companies who feel the same that the day of the Hunter, Jet Provost Gnat etc is far from over.

You may find there are a lot of differences, weight etc is no longer an issue so you can build them out of more robust material.

I believe Siemens have the technical data for the Avon 200 now, they bought it from RR a few years back. Many telecoms faciilities use a couple of Industrial Avons as instant-start power generators.

I think if I was based down at St Athans I would be having very concerned discussions with my CAA surveyor about now, it’s not on the list, but then again there are no Double Mambas on the register at the moment.

Thankyou Consul, I have never seen that report before just the original accident report.
I do feel for the pilot, he did his best to keep that a/c away from built up areas.
The people of Whitehall have shown their true nature by letting him down badly. Some things never change.

http://publicapps.caa.co.uk/docs/33/ProposedMPD1601R1.pdf

Orpheus added

Consul, that is very helpful in understanding the flight characteristics of a Hunter not making power and that glide slope information makes for very interesting reading, great find thank you.

Interesting and detailed report of that Tintagel incident by the pilot of the Hunter concerned here:
http://www.tintagelweb.co.uk/tintagel%20plane%20crash.htm

Tim