Originally Posted by
A and C
The decision to extend the life of the ejection seat pyrotechnics is an interesting one.
The original manufactures will have considered a number of factors when setting the limitation, these are likely to be based on the harshest military operation environment with a good measure of safety and a bit of allowance for the deep pockets of the military budget. Once you start operating the aircraft occasionally without the temp cycles of high level flight and store the aircraft in a comfortable environment the safe life of such devices is likely to extend, it is for those who extend the life of these devices to base this decision on reliable data.
It is vital that the black and white attitude to shelf life is not taken and the date on the packet is viewed in the light of current operational conditions as this can move the date in ether direction to ensure reliable performance.
Actually, the shelf life of the pyrotechnic is determined by batch testing samples. Explosive substances degrade with time, and as you mention, environmental conditions, so the 2-year life will be based on a risk-averse projection of the explosive substance's condition. Extension of the 2-year life will be granted if a sample from the same batch and lot (as identified on the canister) is tested and achieves the specification result.
The 6 -year total life will be a safeguard, but also a cost controller as without representative samples (which have to be withheld from sale and stored securely) you cannot authorise a further life extension.
The OEM's withdrawal of support for the ejection seat is not the stick-out here; equivalent support can be provided. The continued use of time-expired cartridges in the ejection seat is the alarm bell for me, it tells us something of the culture of the organisation operating this aircraft. They should have grounded the aircraft until new cartridges were fitted.
I raised the cultural point in the original thread - but as it had nothing to do with gate-heights, aerobatics and personal hours it was largely rebuffed.
It will be interesting to see what further risks were taken, if any, and whether this is common practice.
Given the howls of denial on this site that flying vintage aircraft could pose any greater risk than military ones, and that flying decommissioned military hardware is likely to remain popular, it would be nice to think that we could learn some valuable lessons from this unfortunate accident.