A22LS Foxbat Rudder Cables

Back in April 2018 I published an item covering the issue of an Aeroprakt Safety Alert concerning inspections and possible replacement of the rudder cables on A22LS aircraft. You can read the article by clicking here: Rudder Cable Safety Alert or the Bulletin itself here: Aeroprakt SB A22LS-17

Following the issue of the Alert, we submitted a pair of the broken cables and a length of new cable to the ATSB for testing and examination. You can view a copy of their report by clicking here: ATSB Report Rudder Cable Analysis Results

The ATSB Report reaches the following conclusions:

  • The primary cause of the RH cable fracture was fatigue, resulting in overstress of the remaining wires.
  • The LH cable was unserviceable (based on manufacturer requirements) due to deformation and wire fractures that were already apparent.
  • The cables and pulleys provided to the ATSB were compliant with the manufacturer’s specifications (pending chemical analysis results).
  • Most of the fatigue would have occurred prior to the accident flight, and it is likely that some would have been present at the last 200-hourly cable inspection (1600 hours).
  • Fatigue in both cables may have been accelerated by the cable running around a smaller diameter pulley than is recommended.

In Summary – please ensure your rudder cables are correctly inspected every 200 hours per the Safety Alert and Maintenance Manual. This does NOT mean a quick glance and a ‘twang’ of the cables behind the seats! At any sign of wear or broken cable strands,  both rudder cables must be replaced.

Finally, please note that the incident aircraft was registered 24-7930 – not, as erroneously stated in the report, 24-7390.

Cleaning A22 Foxbat and A32 Vixxen windscreens

Over the last couple of years, we have received reports of broken windscreens on a very small number of Aeroprakt aircraft in Australia. A couple of these were definitely due to bird strikes. However, the cause of a couple of others has never been finally agreed.

The factory reports a very limited number of screen failures in the rest of the world – I believe two or three more – in addition to those reported in Australia. This is out of a total world fleet of over 1,100 aircraft spanning 22 years of production.

In an effort to establish potential causes, and thus introduce preventative measures, we have agreed to publish as much information as possible and seek owner responses where appropriate.

First of all, the factory wants to emphasise the following points:
1. The windscreen design and material have proven themselves on hundreds of Aeroprakt airplanes. Screen collapse cases are extremely rare and have never been associated with the design, but usually pre-existing cracks.
2. Current windscreens are made not of polycarbonate plastic but of PET (Polyethylene terephthalate), so any ‘polycarbonate approved’ cleaner may not be suitable for PET.
3. The effect of unsuitable cleaners (including gasoline, Windex®, Mr Sheen®, solvents which may be suitable for acrylic screens or any other non-PET approved solvents) on the structural properties is such that the PET glass may become brittle (crack-prone) in stressed areas (although in non-stressed areas it has no such effect).
4. The factory does not make oversize rivet holes in the glass because it makes no sense as the rivets compress – that is, produce stress in – the glass anyway.
5. All-aluminium rivets are used to secure the windscreens. This means every part of the rivet is aluminium – including the shaft, which is not steel, as per regular ‘pop’ rivets.
6. The recommended sealant for PET and polycarbonate windscreen replacement is now an acrylic transparent sealer such as FulaSeal 701, not a silicone sealer, which should be used sparingly. Excessive use of sealer can potentially weaken the screen.
7. Finally, a thicker glass is not a good solution as it will be under even higher stress in the areas where it is formed to the required shape. Therefore it will be even more prone to cracking.

In the past, based on local engineers advice, it has been Foxbat Australia’s understanding that the windscreens of A22 and A32 aircraft were polycarbonate sheet and as part of our new owner pack, we have included a canister of proprietary polycarbonate screen cleaner. We have also in good faith recommended these cleaners to existing owners. None of these products expressly forbids their use on PET, nor can we find any information regarding their suitability for PET – indeed, they all make generic statements like ‘suitable for cleaning all plastics’.

However, at the present time, we strongly recommend that owners/pilots of Aeroprakt aircraft stop using these types of cleaner on their windscreens until such time as their manufacturers confirm without reservation and in writing that they are suitable for PET.

So how should you clean your Foxbat/Kelpie or Vixxen windscreen?
1. We recommend cleaning PET (or polycarbonate) plastics first with a mild solution of soap or detergent and warm water. It is also possible safely to use a specialty cleaning product such as Novus® No.1 or Brillianize.
2. DO NOT use window cleaning fluids with ammonia (such as Windex®, or Formula 409®), Mr Sheen®, gasoline, denatured alcohol, carbon tetrachloride, or acetone, which will cause the plastics to craze with minute cracks.
3. DO NOT use so-called ‘aviation approved’ screen cleaners as these may have been formulated for cleaning other types of plastics.
4. Begin by gently blowing away any loose dust, dirt and dead bugs from the surface. DO NOT use a pressure washer on any part of the aircraft, including the screen.
5. DO NOT use proprietary chemicals (such as ‘Bug Off’) to soften and remove dead bugs from the screen. Simply spray a weak solution of soap and water on the screen and let it soak for 5-10 minutes, re-spraying if needed to keep the surface wet. Then wipe with a wet non-abrasive/non-contaminating/lint-free soft cloth, microfibre cloth, or cellulose sponge. Rinse well with plenty of clean, clear water. You may need to repeat this process a couple of times to remove all dried-on dead bugs.
6. To give a final clean to the screen, apply the specialty cleaning product (or a weak soap and water solution) with a dampened non-abrasive/non-contaminating/lint-free soft cloth, microfibre cloth, or cellulose sponge.
7. Rinse well with plenty of clean, clear water.
8. Pat dry with a chamois leather, damp cellulose sponge, or microfibre cloth to prevent water spotting.
9. Repeat this process regularly to ensure there is no build up of dirt on the windscreen. If possible, clean a dirty screen immediately after flight to stop dirt etc hardening during the time before you next fly.

Thank you for your attention – please leave a comment below if you feel it’s appropriate.

 

Light Sport Aircraft Maintenance

It is my belief that today’s recreational and light sport aircraft need more careful and meticulous maintenance than traditional ‘rag & tube’ ultralights and typical single engined GA aircraft.

Over the last 15-20 years or so, recreational and light sport aircraft have become much more GA-like in their looks and construction, compared with traditional utralights of old.

Their weight and complexity has increased almost beyond the imagination of early ultralight owners; their airframes have become more and more GA-like, with concealed control systems, engine bay ducting which hides many key engine components, digital instrumentation, auto-pilots and the like. Yet recreational aircraft owners and pilots are still permitted to ‘do all their own maintenance’*.

Crucially, recreational and light sport aircraft have to be designed and built to fit under a specific gross weight limit. There is also a maximum empty weight formula related to the maximum gross, which effectively limits the empty weight of a 2-seat aircraft to around half that of a typical 2-seat GA aircraft. As a result, manufacturers have to do everything they can to minimise empty weight – usually by using light weight materials and making components as strong as they need to be, but no stronger.

This lightweight approach is not in itself an issue – indeed it has enabled the design and manufacture of some wonderful aircraft. But in reality, ‘cheaper and lighter’ means you have to be much more thorough with your inspections and maintenance.

Why?

Because the metal is thinner all round; because so-called ‘carbon fibre’ aircraft actually contain very little carbon fibre (if they really were mainly carbon fibre, their cost would be astronomical); because cables are thinner, because engines are smaller/lighter/more highly stressed, because propellers are typically composite not metal; landing gear is lighter; bearings are smaller, tolerances are tighter; and because some of their systems are quite different from typical GA aircraft, and on and on…

Although RAAus is working wonders to improve the safety of aircraft registered with them – particularly focussing on maintenance issues and authorisations to maintain*, I still have considerable doubts as to the maintenance capabilities of many RAAus Aircraft owners, who likely have little or no aircraft maintenance knowledge and experience. I myself know the A22 and A32 airframes inside out but I do not feel at all confident I could safely maintain one.

For example do these owners know:
– how properly to lockwire a bolt, and what thickness and type of wire is required?
– how to measure and adjust the tension of a control or structural cable?
– how and when to use a torque wrench correctly?
– the standard torque settings for each size of bolt?
– how and when to check static and dynamic carburettor balance?
– how to check the friction on the Rotax gearbox clutch?
– how to make sure the ends of a cable are still securely swaged?
– how to measure correctly the strength of the fabric covering on a wing?
– how to open and examine properly an oil filter after an oil change, and what to look for?
– how to check a control or structural cable for internal abrasion and wear?
– how and where to look for cracks in metal/composite/wooden airframes?
– where to place a jack to raise their aircraft?
– how to decide when to replace an ‘on condition’ item?
– what constitutes ‘acceptable’ and ‘unacceptable’ wear in an item?

Not to mention possession of all the tools needed to do these jobs properly?

Now, I’m aware of many aircraft in our Aeroprakt fleet with well over 3000 hours on them – with no particular problems. As I say, maintained properly, recreational and light sport aircraft can continue flying safely for many thousands of hours.

But if you are going to maintain your own aircraft, get proper training to do so – if you skimp on maintenance or try to save money by doing it yourself when you don’t really have the capability, at the very least your aeroplane won’t last as long as it should. And at worst, it will be your life (or that of the pilot) that’s threatened.

* Owners of RAAus registered aircraft may maintain their own aircraft provided they have an L1 Maintenance Authority (sometimes called an ‘Owner-Maintainer’ authorisation). Details of this are available on the RA Australia website at http://www.raa.asn.au  under the member section ‘Member Training’

A22L Foxbat gross weight increase

I have good news for all Australian owners of A22L (450 kilo MTOW limit) Foxbats!

With the new RAAus MARAP system (Modification and Repair Approval Process), a review to increase the gross weight limit (sometimes called the maximum take-off weight (MTOW)) of RAAUS  registered Aeroprakt A22L Foxbat aircraft from 450 kilograms (472.5 kilograms if a ballistic rescue system is fitted) to 525 kilograms has been conducted and now approved.

During the review of the A22L for an increase up to the 525 kilograms  MTOW there is a small ‘G’ limit penalty: the maximum limits are reduced from +4G and -2G to +3.6G and -1.8G respectively. In effect, this means you need to observe manoeuvring and rough air limits closely to ensure you do not exceed these lower limits.

No structural or other changes are required to the aircraft.

To obtain the increased weight limit on your A22L aircraft, please contact the technical team at RAAus – phone number 02 6280 4700 or email to tech@raa.asn.au – and request the necessary documentation. This includes a supplementary page for your pilot manual and an entry to the manual revisions page.

RAAus will make a charge for this service but I’m sure you’ll find the extra – legal – 75 kilograms well worth it!

Please note, this increase is not relevant to the Aeroprakt A22LS Foxbat, which already has a gross weight limit of 600 kilos and ‘G’ limits of +4 -2

Aeroprakt issues rudder cables safety alert

Example of cable damage


Following two rudder cable breakages on A22LS aircraft, the Aeroprakt factory has issued a safety alert covering all A22 and A22L aircraft with over 500 hours engine running time and all A22LS and A22L2 aircraft over 5 years old or over 500 hours engine running time.

The alert requires an urgent check of both left and right rudder cables to ensure there is no wear or fraying of the cables, particularly close to the pulley guides. If any wear is seen or broken strands are found, the rudder cables must be replaced.

Click here to download a copy of the alert for A22 and A22L aircraft.
Click here to download a copy of the alert for A22LS and A22L2 aircraft.

Australian owners should contact Foxbat Australia for more information or replacement cables. Owners in other countries should contact their local dealer for support.

A32 Vixxen door latches – safety bulletin

Aeroprakt has issued a safety bulletin covering the door latches on A32 Vixxen aircraft, serial numbers 02-28. Compliance with this bulletin is required before the next flight of the aircraft.

Click here or on the drawing above for a copy of the bulletin: SA-A32-03 Door Latches

Rotax 912 series oil filter – new service bulletin

Rotax has issued a new mandatory service bulletin covering their oil filters – SB-912-071.

Due to a manufacturing deviation, the sealer gasket on the oil filter may leak, causing possible loss of oil pressure and oil.

If your 912ULS engine number is within the series from S/N 9 569 542 up to S/N 9 569 782 inclusive, or you have service replaced your oil filter since June 2017, you need to check the filter. If it has a green mark in the specified location, the filter is OK. If not, check for leakage and if any is seen, the filter must be replaced immediately. Even if there is no visible leak, the filter must also be replaced immediately on listed engines.

If there is no green mark on the filter, no leakage and the engine is not listed, the filter should be replaced within 25 engine running hours or within 200 days from 01 November 2017, whichever occurs sooner.

Here is a link to the service bulletin which gives full details: SB-912-071
Here is a link to the listed 912UL & 912ULS engines affected: SB-912-071UL