Flying Creatures and Hit Point Loss

[Lee's Fortune]

What are the rules as far as flying creatures and losing hit points? I recall a rule about certain flying creatures (with wings, I believe) being forced to land if they are down to just a quarter of their hit points. Was this in a previous edition and I'm just confused?

 

[frankthedm]

2nd edition had that rule IIRC.

1E did not and i recall a DL module having a fairly strong white dragon fly away if reduced to 10 or less HP.

this edtion is no flight if in medium or heavy load & no flight in medium or heavy barding.