Stored procedure : Data truncation: Truncated incorrect DOUBLE value - mysql

Question

I lack experience building stored procedures and have encountered this error that I cannot understand the reasoning behind :
[2015-09-29 01:01:55] [22001][1292] Data truncation: Truncated incorrect DOUBLE value: '5609d3e6c89be'
The value '5609d3e6c89be' is the "FlightID".
My stored procedure code :
DROP PROCEDURE IF EXISTS initFlight;
CREATE PROCEDURE initFlight (flightid VARCHAR(50))
BEGIN
-- rules, player should only fly if not in jail, not in missions
-- and is in the city the flight will take off from
DECLARE fname VARCHAR(50); -- flight name
DECLARE depart int; -- city number of departure
DECLARE dest int; -- city number of destination
-- assign values to our variables
select flightname, source_airport, destination_airport
into fname, depart, dest
from airport_flights where id = flightID;
-- show in console the variable values for debugging
-- select concat(" fname: ", fname, " depart: ", depart, " dest: ", dest);
-- set players flying means p.live = '-1'
update `[players]` as p set p.live = '-1' where p.id in (
select id from airport_tickets where flight = flightID
) and p.live = depart;
-- insert into alerts a message for players boarding the flight (are in the city of departure)
insert into player_alerts (alert_text, player_id)
select concat("Boarding flight ", fname) as alert_text, p.id as player_id from `[players]` as p
where p.id in (
select id from airport_tickets where flight = flightID
) and p.live = depart;
-- insert into alerts a message for players that missed the flight (are not in the city of departure)
insert into player_alerts (alert_text, player_id)
select concat("You missed flight ", fname) as alert_text, id as player_id from `[players]` as p
where p.id in (
select id from airport_tickets where flight = flightID
) and p.live != depart;
-- stop sales
update airport_flights set selling_tickets = 0 where id = flightID;
END;
call initFlight('5609d3da016bf');
What is happening here? Why is my "string" being coverted into a double and then truncated?
airport_flights.id is varchar(50)
airport_flights.source_airport is int(11)
airport_flights.destination_airport is int(11)
airport_tickets.id is varchar(50)
airport_tickets.flight is varchar(50)
airport_tickets.owner_id is int(11)
`[players]`.id is int(11)
`[players]`.live is int(11)
`[players]`.name is varchar(200)
player_alerts.id is int(11)
player_alerts.alert_text is varchar(250)
PS: if you need any more information let me know and criticism is as always welcome

Answer 1

After much head bumping around I found out that the problem was in the sub-queries where I was mixing the airport_tickets.id (varchar) with the player.id (int) when I wanted to match airport_tickets.owner_id with player.id.
I only found this out when removing everything and re-writing it all as a measure of removing any code blindness (when your brain reads what it thinks the code does instead of what is actually written).