If the only thing the Airlines table is used for is to do lookups to derive airline logos, then I'd recommend we change the primary key to C2 (the IATA code).
Change should be possible in the installer, or at first-run of the new v3 app. Using SQL like this:
CREATE TEMPORARY TABLE airlines01(
CN,
C3,
CM,
C2
);
INSERT INTO airlines01
SELECT
CN,
C3,
CM,
C2
FROM airlines;
DROP TABLE airlines;
CREATE TABLE airlines (
CN varchar(80),
C3 varchar(6),
CM varchar(6),
C2 varchar(6) PRIMARY KEY NOT NULL UNIQUE
);
CREATE INDEX iC2
ON airlines
(C2);
CREATE INDEX iC3
ON airlines
(C3);
INSERT INTO airlines
SELECT
CN,
C3,
CM,
C2
FROM airlines01;
DROP TABLE airlines01;