Make it a bit easier to debug when airlines= is malformed

final/AS/HKG/source/VHHH_PC.txt

@@ -1,6 +1,7 @@
 [meta]
 header = VHHH TMA 1.0.0
 	See VHHH_PC_readme.md
+callsigns = True
 
 [airspace]
 radius = 100

tools/expand.py

@@ -63,6 +63,7 @@ class Airline:
         self.frequency = int(frequency.strip())
         self.types = types.strip()
         self.callsign = callsign.strip()
+        try:
             if Airline.callsigns is not None and Airline.use_callsigns:
                 if '-' not in callsign:
                     self.pronunciation = Airline.callsigns[callsign]
@@ -78,13 +79,15 @@ class Airline:
                 self.pronunciation = data[0].strip()
                 data = data[1:]
             if gateways is not None:
-            directions = []
                 arrival_gateways = {gateway.strip() for gateway in data[0].split("/")}
                 departure_gateways = {gateway.strip() for gateway in data[1].split("/")}
                 self.directions = "".join(sorted(
                     {gateways[gateway] for gateway in arrival_gateways | departure_gateways}))
             else:
                 self.directions = data[0].strip()
+        except Exception as e:
+            raise ValueError(f"Could not create airline from ({callsign}, {frequency}, {types}, {str(data)})" +
+                f"\nCallsign pronunciation lookup = {Airline.use_callsigns}") from e
 
 
 def process_fix_list(fix_list, fixes):