The lack of an underscore between "chartered" and "flight" in the table name appears to be the cause of the problem you're seeing. I'm assuming you want something along this lines, with the table's name being chartered flight.
CREATE TABLE chartered_flight(flight_no NUMBER(4) PRIMARY KEY
, customer_id NUMBER(6) REFERENCES customer(customer_id)
, aircraft_no NUMBER(4) REFERENCES aircraft(aircraft_no)
, flight_type VARCHAR2 (12)
, flight_date DATE NOT NULL
, flight_time INTERVAL DAY TO SECOND NOT NULL
, takeoff_at CHAR (3) NOT NULL
, destination CHAR (3) NOT NULL)
Generally, there is no benefit to declaring a column as CHAR(3) rather than VARCHAR2(3). Declaring a column as CHAR(3) doesn't force there to be three characters of (useful) data. It just tells Oracle to space-pad data with fewer than three characters to three characters. That is unlikely to be helpful if someone inadvertently enters an incorrect code. Potentially, you could declare the column as VARCHAR2(3) and then add a CHECK constraint that LENGTH(takeoff_at) = 3.
CREATE TABLE chartered_flight(flight_no NUMBER(4) PRIMARY KEY
, customer_id NUMBER(6) REFERENCES customer(customer_id)
, aircraft_no NUMBER(4) REFERENCES aircraft(aircraft_no)
, flight_type VARCHAR2 (12)
, flight_date DATE NOT NULL
, flight_time INTERVAL DAY TO SECOND NOT NULL
, takeoff_at CHAR (3) NOT NULL CHECK( length( takeoff_at ) = 3 )
, destination CHAR (3) NOT NULL CHECK( length( destination ) = 3 )
)
You should should create a distinct collection of valid airport codes and establish foreign key restrictions between the chartered flight table and this new airport code table because takeoff at and destination are both airport codes. This makes it much simpler in the future if an airport code changes and guarantees that only legitimate airport codes are added.
I hope this helps you.