Tail Unit Bracing Warning

[Guest TOSGcentral]

I am putting a notice up about this now as the next TOSG Bulletin is still over a month away.

 

 

The main point that I want to make here is the need for precision and checking routine in maintenance procedures – plus it helps if you know what the hell is supposed to be going on! Another factor is the need to be constantly on guard against complacency because you do so much without trouble – then miss a ‘biggy’.

 

 

Situation #1. There are few days when either Lois or I, or both of us, are not on the spanners with the four Thrusters that we are currently working on – we are covering a lot of varied work and much of it is ‘work in progress’ and has to be left while we wait for parts or repairs we cannot handle ourselves. So there is a fair bit of mental pressure there to keep track of where we are up to at any one time, that worksheets only partly counter.

 

 

One of the aircraft is a T500 that we have in for total inspection, overhaul and remedial action on some of the airframe. Part of this was totally dismantling the tailwheel assembly, correcting it’s geometry and fabricating a correct steerage linkage for it.

 

 

The front retaining bolt for the tailwheel spring also doubles as the retaining bolt for the tailplane lower bracing cables tang. The simple way is to dismount the double tang and leave the cables attached. This leaves the bracing cables looking apparently normal to a casual glance.

 

 

We wanted to check the geometry of the revised unit so there was no intention of finishing the job at that time so the double tang was not re-mounted when the tailwheel went back on. The geometry came out perfect so we measured up and returned to the workshop to fabricate the steering linkage.

 

 

Returning to the hangar to complete the job we had people amble in who wanted to ask questions, have us look at their aircraft, socialise, or just chat-up Lois. This is highly distracting! In consequence the double tang for the bracing cables was not re-mounted.

 

 

This left an aircraft ready for test flying, that outwardly looked entirely normal, but had part of it’s primary structure entirely disconnected!

 

 

That was not of much account because part of our maintenance procedures are to leave a ‘finished’ job and return to it cold a bit later and critically inspect not simply the work but the integrity of the airframe in overall context. The error was immediately found and corrected.

 

 

The safety points to come out of this are:

 

 

• Be prepared to critically check yourself and preferably have an independent inspection (that Lois and I are easily able to do between us but a lot of people working alone are not) and make this part of an inflexible working routine.
   
   
  
• Always remember that even though something may ‘look right’ it may not be until it has been functionally checked.
   
   
  
• Part of a functional check is not taking an unairworthy machine into the air to see if it works – be damn sure it will work first!
   
   
  
• Do not tolerate intensive interruptions when you are working on aircraft. This can be hard in a recreational environment but ultimately it is better to be rude than dead!
   
   
  

 

 

The above may be interesting and is certainly benign. The following is not!

 

 

Situation #2. Recently I had one of my rare field trips by combining some airframe inspections and advice with picking up an aircraft from Canberra by trailer.

 

 

One of these was a T300 that has some fundamental weight and balance problems that has been ‘creatively addressed’ by the owner. This worthy is a nice guy, an ex commercial GA pilot, and openly admits that he knows little about ultralights – yet has free rein to do substantial work on them via the automatic L1 authority.

 

 

In the course of conversation with the L2 who had done the current RAAus AN on the tail unit. He said that he had done the crack testing, found no fault, and left the owner to put the aircraft back together – which is fair enough as it is not operated in a school.

 

 

The owner appears to have become a bit tangled up and had disconnected that lower bracing tang referred to above. Even though he had not reattached this, the tail unit outwardly appeared normal and he employed no checking procedures – he then flew the aircraft, for about 3 hours!

 

 

The only thing that saved him was that there is normally a downwash on the tail unit that kept it in place, plus the very robust Thruster structure and some good condition rear tail unit bushes otherwise the tail would have come off. The L2 picked up the problem immediately the aircraft flew into his own strip and rectified the problem.

 

 

A further problem is that the owner could not have completed the AD (that he is entitled to sign off) as the required tensioning of the tail unit was not done – in fact there was NO bracing tension on it at all top or bottom!

 

 

Some conclusions and advice. Now I am feeling a bit bleak about all this! Not only have we had two very similar occurrences, 800 km apart, within two weeks of each other – this has happened when we should have all been very revved up by the tail of a TST very nearly falling off in flight. TOSG has already opined that tail unit bracing tension may be a contributory factor and this is in the AN.

 

 

If the unsecured tail unit of that T300 had come off in flight – which was quite possible as it was not braced at all – then it would have been fatal and while the cause would (probably) have been found that may be weeks or months down the track.

 

 

In the meantime EVERY Thruster in the country would have been grounded! That impacts on us all! This does not apply just to Thrusters it could equally apply to any similar aircraft, or for that matter any aircraft.

 

 

We have to lift our act on maintenance procedures and aircraft type knowledge or we are all going to pay the consequent price!

 

 

In the next TOSG Bulletin there will be one Helluva rev about this circumstance and some very blunt advice on how to keep your backsides out of a sling.

 

 

Aye

 

 

Tony