SNS3Guppy re your statement – “Aircraft most certainly are not designed to withstand entry into cumulonimbus storms”.
I suggest that a more circumspect approach is required.
We may have differences in our opinions or in the use of the wording between ‘entry into’ and ‘withstanding inadvertent entry’.
There could also be differences in the design and certification levels of the aircraft being considered. A light aircraft or bisjet might not meet the structural requirements of FAR/JAR 25 - Large Commercial Aircraft; the aircraft which I flew did (but it was still damaged).
In my experience I have yet to see a commercial aircraft flight manual which prohibits fight into cbs i.e. a restriction requiring avoidance ‘at all cost or else’. This suggests that those aircraft have at least some protection against inadvertent cb entry, but there again not all cbs are equal! Similarly this does not imply that flight into cbs should be done.
A major point of my response is to avoid leaving some pilots with the belief that an inadvertent entry into a cb will be fatal. It certainly will be hazardous and the situation should be avoided, but provided the manufacturer’s advice is followed the aircraft should remain structurally sound albeit slightly dented.
Aircraft that do not survive cbs might have been handled incorrectly, thus placing them beyond design limits, or in some circumstance the aircraft could already be structurally weak. Examples of the latter can be found in reports of turboprop accidents in S America; structural inspections were not completed – post accident inspection identified pre existing wing cracks.
This topic is a good example of Threat and Error Management. The threats from a cb should be identified and avoided, but if through error – failure to identify, equipment failure, or human involvement, then the resultant (inadvertent cb entry) must be managed. This can be done by following AFM advice which is designed to mitigate (not eliminate) the risk of the threat and/or error.