the ads:

package Airlines_Package is
    type Airlines( Size: Positive ) is limited private;
    procedure Init( P: out Airlines );
    procedure AssignName( P: out Airlines; Index: in Positive; Name: in String );
    procedure InsertFlight( P: out Airlines; From, To: in String );
private
    type Matrix is array ( Integer range <>, Integer range <>) of Boolean;
    type NamesArray is array ( Integer range <> ) of String(1..10);
    type Airlines( Size: Positive ) is record
        Names: NamesArray( 1..Size );
        Flights: Matrix( 1..Size, 1..Size );
    end record;
end Airlines_Package;

the adb:
package body Airlines_Package is
    procedure Init( P: out Airlines ) is
    begin
        for I in 1..P.Size loop
            for J in 1..P.Size loop
                if I = J then
                    P.Flights(I, J) := True;
                else
                    P.Flights(I, J) := False;
                end if;
            end loop;
        end loop;
    end;
    procedure AssignName( P: out Airlines; Index: in Positive; Name: in String ) is
    begin
        for I in 1..10 loop
            P.Names(1)(I) := ' ';
        end loop;
    end;
    procedure InsertFlight( P: out Airlines; From, To: in String ) is
    begin
        declare
            FromIndex, ToIndex: Integer := -1;
        begin
            for I in 1..3 loop
                if P.Names(I) = From then
                    FromIndex := I;
                elsif P.Names(I) = To then
                    ToIndex := I;
                end if;
            end loop;
            P.Flights(FromIndex, ToIndex) := True;
            P.Flights(ToIndex, FromIndex) := True;
        end;
    end;
end Airlines_Package;

and the test program (main.adb):
with Ada.Integer_Text_IO, Airlines_Package;
use Ada.Integer_Text_IO, Airlines_Package;
procedure Main is
    Q: Airlines(3);
begin
    Init( Q );
    AssignName( Q, 1, "Wien" );
    AssignName( Q, 2, "London" );
    AssignName( Q, 3, "Prague" );
    InsertFlight( Q, "Prague", "London" );
end Main;

the error:
nagyz@platoon:~/ada$ gnatmake main
gcc-4.1 -c main.adb
gcc-4.1 -c airlines_package.adb
airlines_package.adb:27:20: warning: "P.Names" may be referenced before it has a value
gnatbind -x main.ali
gnatlink main.ali
nagyz@platoon:~/ada$ ./main

raised CONSTRAINT_ERROR : airlines_package.adb:33 index check failed
nagyz@platoon:~/ada$