A forward slip is WELL within the envelop on a Boeing
Interesting ENVELOP????? Spelled twice this way in the post.
Now it's time for DVT to go back to MS Flt sim and practice his/her short field landings in the Concorde.
At least this line of rationale is reassuring to a PPL who travels as pax rather a lot and would feel very uncomfortable about anyone needing to slip an airliner, certainly whe he should be stabilised.