From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of John Smith
Sent: Monday, February 24, 2014 7:32 PM
To: lml@lancaironline.net
Subject: [LML] Re: Legacy Accident History Update

Hi Valin,

I'm glad you are on the case as well…..  Hope following helps a little?

As you know, there has been a fair bit of dialogue on the canopy issue on the forum. And a while back, I invited forum members to join in a working group to look at the issue and, in particular, look at a safety latch. The outcome was no takers other than colleagues here in Oz. Whilst a few of us already had dual micro switch warning systems installed in our Legacy's, but sadly not the Gerladton or Shepparton Legacys, myself and a few colleagues have been feverishly working on a safety latch design to further reduce risk of the canopy open event.

Cutting straight to where I, and no doubt others may have already got to, but quite likely not all…….

• Make sure you have check lists that include the canopy status at run-up, and then again at the holding point / line-up – and use them
• Develop and acknowledge canopy open on ground and in air procedures

• if on the ground and it opens, whatever – do not proceed to airborne
• If it opens in the air – above all else, do not attempt to close the canopy, keep the ball centered

• Add a pair of warning switches in series to check for latch position and canopy seat position – wire so fail safe – audible + big visual warning

A bit more detail below…..particularly around the risk assessment.  Read on if you're still interested!

As far as a safety latch is concerned, our group here would have between us come up with dozens of different designs, some of which were sufficiently well developed that one could almost start building the CAD drawings / CNC machine inputs files for fabrication of components. The goal was of course to design something that will operate safely and reliably, not hinder egress or external emergency access, and be simple to install both during a build and after build. We short listed a few options, but all required some penetrations in the structure - so I passed these options to Lancair to see if they could provide guidance as to which would be acceptable from a structural point of view – to date no response (I must follow up…). Once we get that guidance, I will most likely build a prototype and install on my Legacy.  I fully intend to publish / share whatever we come up with.

Above said, I had forgotten about Don Barnes' solution where I understand the canopy sits up a little bit unless the canopy latch is in the closed position – that may well largely obviate the need for a safety latch, as I'd presume the noise with even with a slightly open canopy (and even with noise cancelling headsets) would be hard to miss – but may be not 100% fool proof. Anyone know how high the canopy sits up with this mod?  1/2"? 1"?

In order to try and bring a bit of rigour and quantification to the understanding of risk and what measures are useful or not and so forth, I have also done a fair bit of work with event tree analysis to assess how various combinations of check lists, procedures, warning devices and a safety latch effect the risk of a fatal canopy open event. The event tree input assumptions around probabilities of various actions were tuned to match the actual historical risk of a fatal canopy open event.  I found it a powerful way to explore what might happen if one does or does not do or have something…  Very interesting, and not entirely or always intuitive. There is no doubt that a secondary latch gets straight to a really good outcome – provided such mechanism does not present unintended additional risk or compromise structural integrity. I am happy to share in the detail of this "model" if anyone is interested, but the bottom line messages - and noting the inherent uncertainty around many of the inputs and assumptions - of this work were:-

• At the time I did the work, there had I believe been 3 fatal canopy open events - this equates to a risk factor in the order of 3 x 10-5 (unacceptable cf. a generally understood overall risk target for GA of 10-6)

• This is expressed as risk of a fatal canopy open event per take-off (you can see basis below)

• A dual microswitch warning system (latch position and canopy position) with audible and visual annunciation - in the case of VH-XTZ and VH-ZYA, we have ~3" x 1/2" flashing red warnings in centre of each EFIS screen, combined with the check lists and defined canopy open event flight procedures, get one into the 10-7 event frequency region (again expressed as frequency per take-off) for a canopy related fatal. If it were expressed as a frequency per hour, the number probably wouldn't look different – if avg. flight times were around 1 hour
• So - in theory a Legacy with a decent warning system operated with a decent (and practiced) canopy related check list and acknowledged emergency procedures, may offer the opportunity to reduce the risk by 2 orders of magnitude (100 times less) compared to aircraft without these measures in place
• A big assumption in all this, is that the historical fatal canopy open event aircraft did not have safety switch systems installed – if anyone knows the answer to that question, I'd appreciate it
• A secondary latch (without an alarm) gets one straight into the 10–8 region or better (albeit this is quite sensitive to the secondary latch reliability assumption)   
• With a warning system AND a secondary latch, the risk goes to zip

John


John N G Smith
Tel / fax:    +61-8-9385-8891
Mobile:      +61-409-372-975
Email:         john@jjts.net.au