SELECT lb.NGAYDI
FROM LICHBAY 
WHERE NOT EXISTS(
	SELECT lmb.MALOAI
	FROM LOAIMB lmb
	WHERE lmb.HANGSX = 'Boeing' AND NOT EXISTS(
		SELECT lb2.MALOAI
		FROM LICHBAY lb2
		WHERE lb2.NGAYDI = lb.NGAYDI)
		)