Firstly, there were reports of unintended canopy jettison or near-jettison on at least two occasions. The red knobs on the right hand side of the cockpits were found to be rearward (near the jettison position) as shown in the photo. Stephen sent out a warning notice to members to be vigilant about this.
(This can also happen if the canopy is open and caught by a gust that is sufficiently severe to tear the gas strut from its latch.)
On inspection, we found that there was indeed a new crack in the canopy, and that the hinges were bent.
So we had two problems; firstly, to understand and correct why the jettison knob seems to move or get moved unintentionally and secondly, to repair and refit the canopy.
Unintended jettison
We assume that either the jettison knob is working back on its own, or that it is being pulled inadvertently and not reset properly.
There appears to be no spring in the jettison mechanism to hold it closed, and to prevent it creeping rearwards. This is a bit unusual, and Tim is trying to get information and assistance from Centrair, the original manufacturer and Type Certificate holder. He has also involved the BGA’s Chief Technical Officer.
At the present time we are still awaiting any response from Centrair, they are notoriously unresponsive in providing support, or even answering emails, even when written in French.
As you can imagine, we have several ideas how to improve the mechanism to prevent these problems but we cannot carry out any unapproved modifications.
That’s where we are at the moment, once the canopy is repaired and refitted the Alliance will be serviceable with continued monitoring of the jettison knob position.
Canopy repair
The crack has been repaired; you might be interested in how we do this.
Essentially, the crack is cut to a vee, and filled with acrylic bonder. This has to be done on one side first, with two or three runs of bonder applied and left to cure. Then the canopy is turned over, and the procedure repeated on the second side. The photos give an idea of the process.
The winter is not a good time to do this, as the bonder needs ideally about 20 deg.C to harden. The bonder absolutely stinks so this cannot be done in any living areas, although the canopy can be moved indoors once it has gone off and the odour has diminished.
The finished repair can be cut back and polished, but we will not attempt that until the summer, when the bonder will have become hard enough and the temperature more suitable.
What is left to do?
The hinges need straightening again; we have trial fitted the canopy and find that the jettison mechanism is jamming when the canopy is closed.
There is a concern that repeated straightening will weaken or crack the hinges, so this has to be done with care. We will use a dye penetrant test to reveal cracking, both before and after straightening the hinges. Hopefully this will work out OK, and the canopy will be serviceable again.
We hope to get this done before Christmas, once we can get adequate access to the Alliance in the hangar. Once again the weather is delaying us.
Tim or I would be happy to answer any questions you may have, meanwhile I hope this helps to explain what has been going on and why it is taking some time.
Barry Lytollis
