Flexible Handling Of Duplicates Using A Trigger

I'd like to achieve the following (and YES, I do know that this is not multi-user safe, but that's not the point here):

Before inserting a record, the trigger shall check if there's already a duplicate one. Duplicate means in this case when there is an intersection of the time frame, defined by two numeric timestamps. That's also the cause why I cannot use a simple UNIQUE constraint here (in my opinion).

Okay, that already works (see code below). But now I need colliding records to be written to a temporary table so that those records can be returned and presented to the user for selection.

create or replace
TRIGGER TRIGGER1
BEFORE INSERT ON FLIGHT_TABLE
FOR EACH ROW
BEGIN
FOR fs_entry IN (SELECT * FROM FLIGHT_TABLE)
LOOP

[Code] .........