A couple things:
DISTINCT icao, fullname, range, weight ...
That looks for ALL of those fields as DISTINCT, you'd want to do DISTINCT(icao).
Aside from that, you might be looking to use GROUP BY instead of DISTINCT
edit: nevermind on the GROUP BY
edit: I see the problem.
Enclose field names with `:
$sql = 'SELECT DISTINCT `icao`, `fullname`, `range`, `weight`, `cruise`, `maxpax`, `maxcargo`, `imagelink`, `downloadlink`
FROM `' . TABLE_PREFIX . 'aircraft`
WHERE `enabled` = 1 ';