### Database Schema:
CREATE TABLE Airlines (
	FL_DATE	TEXT	NULL,
	OP_CARRIER_AIRLINE_ID	INTEGER	NULL,
	TAIL_NUM	TEXT	NULL,
	OP_CARRIER_FL_NUM	INTEGER	NULL,
	ORIGIN_AIRPORT_ID	INTEGER	NULL,
	ORIGIN_AIRPORT_SEQ_ID	INTEGER	NULL,
	ORIGIN_CITY_MARKET_ID	INTEGER	NULL,
	ORIGIN	TEXT	NULL,
	DEST_AIRPORT_ID	INTEGER	NULL,
	DEST_AIRPORT_SEQ_ID	INTEGER	NULL,
	DEST_CITY_MARKET_ID	INTEGER	NULL,
	DEST	TEXT	NULL,
	CRS_DEP_TIME	INTEGER	NULL,
	DEP_TIME	INTEGER	NULL,
	DEP_DELAY	INTEGER	NULL,
	DEP_DELAY_NEW	INTEGER	NULL,
	ARR_TIME	INTEGER	NULL,
	ARR_DELAY	INTEGER	NULL,
	ARR_DELAY_NEW	INTEGER	NULL,
	CANCELLED	INTEGER	NULL,
	CANCELLATION_CODE	TEXT	NULL,
	CRS_ELAPSED_TIME	INTEGER	NULL,
	ACTUAL_ELAPSED_TIME	INTEGER	NULL,
	CARRIER_DELAY	INTEGER	NULL,
	WEATHER_DELAY	INTEGER	NULL,
	NAS_DELAY	INTEGER	NULL,
	SECURITY_DELAY	INTEGER	NULL,
	LATE_AIRCRAFT_DELAY	INTEGER	NULL,
	foreign key (ORIGIN) references Airports (Code),
	foreign key (OP_CARRIER_AIRLINE_ID) references `Air Carriers` (Code),
	foreign key (DEST) references Airports (Code)
);

CREATE TABLE Airports (
	Code	TEXT	NULL	PRIMARY KEY,
	Description	TEXT	NULL
);

CREATE TABLE `Air Carriers` (
	Code	INTEGER	NULL	PRIMARY KEY,
	Description	TEXT	NULL
);

### User's Query:
Among the flights with air carrier "Southwest Airlines Co.: WN", provide the tail number of flights with an actual elapsed time lower than the 80% of the average actual elapsed time of listed flights.

### Extra Knowledge:
Southwest Airlines Co.: WN refers to Description = 'Southwest Airlines Co.: WN'; tail number refers to TAIL_NUM; actual elapsed time lower than the 80% of the average actual elapsed time refers to ACTUAL_ELAPSED_TIME < (MULTIPLY AVG(ACTUAL_ELAPSED_TIME), 0.8);
SELECT T2.TAIL_NUM FROM `Air Carriers` AS T1 INNER JOIN Airlines AS T2 ON T1.Code = T2.OP_CARRIER_AIRLINE_ID WHERE T1.Description = 'Southwest Airlines Co.: WN' AND T2.ACTUAL_ELAPSED_TIME < ( SELECT AVG(ACTUAL_ELAPSED_TIME) * 0.8 FROM Airlines )