if you had fixed a placard in front of the righthand seat worded
appropriately, but basically stating... if you fly in this aircraft you do so at
your own risk, so therefore anyone flying would be deemed to have accepted those
terms!
What is deemed negligent? For example, you suffer engine failure
due to mechanical failure then in the ensuing forced landing run into power
lines and kill your pax, would you in those circumstances be liable to a claim
against you?
Despite frequent signs that may suggest otherwise, English law does not allow you to exclude liability for causing death or personal injury through negligence.
IN answer to your second question, negligence is basically a combination of two things: 1) owing a duty of care to someone and 2) failing to discharge that duty of care. Whether or not you owe a duty of care to someone is largely a matter if law. You will owe a duty of care to passengers and pretty much anyone who is foreseeably affected by your actions. Whether you fail to discharge that duty is partly a question of fact and begins with an assessment of the standard of care required. Having an accident (even if it kills or injures someone) does not in itself equate automatically to negligence. To use an example, a freak weather event causing a CFIT beyond anyone's ability to control it, is not evidence of your negligence. There is a big grey area though. Your actual example would require closer examination. One would need to consider, for example, whether hitting the power lines was caused by a failure to use the skill expected of a PPL holder when executing a forced landing.