Jet Engine Maintenance

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Jet Engine Maintenance

A write-up of a visit, not a handbook.
Airplane

The whole maintenance complex is a one-stop facility for airframe, engine and component maintenance and repair, situated fairly close to the city (Christchurch) airport.

It was built and developed as a 'Gold Standard' facility – that is, one that can be (and is) used as a resource by operators around the world and by them as a reference, too, for their own maintenance facilities. Overall, the test equipment is maintained at at least an order more precise than the equipment it serves.

Incidentally, the recent earthquakes caused little damage – one part of one wall of the hangar – and it was not significant. That was due, perhaps to the local geology and perhaps because it's some distance from the city centre – though not all that far, as those distances go.

Our interest here, the Engine Centre, is next-door but-one to the airframe hangar, the intervening space being taken up by a large open sump – which we'll come back to later.
Owned jointly by Pratt – Whitney (51%) and Air New Zealand, it is certified and approved for an impressive list of operations and employs some 420 people, the great majority of whom are highly skilled (very). On this visit, only a few females were seen at work – in a definite minority but, they are there.

As you know or can guess, these engines are stripped of their casings and fitted into frames when they arrive and are moved to enclosed bays to be worked on. They look and are, vastly complicated and make uninitiated minds boggle when trying to encompass their sophisticated complexity.

Full maintenance of an engine, any engine, is scheduled to be complete within a maximum of 60 days which is rarely exceeded, older engines requiring more work, therefore more time, than later ones. Luckily (or perhaps by design?), apart from wear – tear the more modern ones usually require only small tweaks,. This has, understandably, come to mean that nowadays it's human error that is the greatest problem so you can imagine the quality assurance measures that are in force...

Over time, huge advances have been made, the greatest improvements having been from the use of new materials – but not forgetting design. An illustration of the aspect is that the turbine blades on the engine we viewed were a then new design, using a new construction and new materials, by Rolls-Royce – the costs of that project were the cause of their aero division demise.

As far as possible simple techniques are used, like little screw-in, magnetic, witness plugs that do nothing but collect a little of any stray steel dust that may be loafing around selected areas – unscrew them, inspect them, log the results (then clean them). Compare with previous results and – voila, one indication of health, when viewed alongside other tests.

Careful, advanced design has meant that vulnerable components are less difficult to access and test – crack detection using fluorescent liquids and magnetic techniques using (very fine) iron filings are part of the repertoire.

So far, we have the engine stripped down as far as appropriate, components tested and where necessary repaired or replaced, then it's all reassembled (checked at every stage and – all tools present? ) then checked again.

Next step, Test it.

Onwards, on its test rig, to the Engine Test Facility which, as you can imagine, is built like the proverbial ~house, to contain lateral damage from an accident and deflect it upwards.

From the maintenance area through massive doors (made in Finland weighing 8 tonnes and 9 tonnes), into the test area where it's transferred to another, more substantial rig and placed in position.

Now this building was designed, naturally, for purpose and was to be fitted out in such-and-such a way so as to meet the usual requirements. The locals, however, being the ones who were actually going to use it, asked for – nay, insisted on, two major changes, dug their heels in and won through.

  • One: the control console was made and is maintained locally, which means that any problems are fixed without flying in(!) expertise from, er, elsewhere.
  • Two: (and this was quite a problem) they insisted that, in addition to the cameras inside the test chamber, they had a window (and not of domestic glazing) between control room and test chamber.
  • This has proved its worth on more than one occasion, the Mk1 eyeball being significantly more effective than the best camera in some circumstances.

The outlet is suitably guided outwards. Nothing was said and no-one asked "upwards too?" or "what about wind carrying it to the inlet?" though one can imagine that that was taken into account.

The air intake is from above, through vanes to remove vortices and to approximate laminar flow, then through a wire grill to remove debris that could damage the engine. It doesn't catch birds (or very rarely). It does, however, catch the occasional bumble bee but the frequency is pretty consistent so that population doesn't seem to be affected.

Harking back to that sump. It will hold the test building's worth of water in the event of necessity. If the sprinklers go on (sprinklers? Ha!), after a couple of seconds there's not enough air-space in there to breathe, if you were daft enough to try.

These engines run on kerosene and 65% is needed to keep the engine running – all those moving parts, control systems and friction, as well as the engine elf.

That leaves 35% to provide the thrust to move the engine plus wings plus fuselage plus all the other bits and pieces required to carry you, family and luggage from here to there and back again without incident.

Recent improvements in design and materials have meant fuel savings. Quoted was more power using less fuel amounting to some 4% improvement in efficiency in recent years – small maybe, but significant in this context.

Now you know why flying is so expensive – and if it's not, then...

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Rod

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