I've never been in a plane crash and hopefully never will but if you are in a plane crash and get injured and live then yes it would likely be painful to be in a plane crash.
There have been a few people who have survived plane crashes and only suffered slight injuries and those people were lucky.
However if you're in a severe plane crash and you die it could either be instant death upon crashing or you could lay in the plane or sit in the planes seat either burning alive or slowly dying of injuries including internal injuries.
Some people die instantly while others may suffer for awhile until their death happens.
There's no way to tell for sure.
Although in most cases of deaths from plane crashes the death is instant upon impact which is a good thing if you're gonna die it's better to die right away and not suffer in any pain.