SAL = IATA code for San Salvador, in El Salvador, Central America.
Agreed no problem from GLA to SID (Ilha do Sal, Cape Verde islands). SID used to be a very frequent, although albeit unscheduled, "splash & dash pit-stop" for numerous airlines' full B707s and DC-8s, which had intended operating non-stop from EZE, GIG & VCP etc in South America, onwards to their European destinations.